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I have a string like the following:
String str = "4*5";
Now I have to get the result of 20 by using the string.
I know in some other languages the eval() function will do this.
How can I do this in Java?
You can use the ScriptEngine class and evaluate it as a Javascript string.
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");
Object result = engine.eval("4*5");
There may be a better way, but this one works.
There is no standard Java class or method that will do what you want. Your options include:
Select and use some third-party expression evaluation library. For example JEL or any of the half dozen libraries listed here.
Wrap the expression in the Java source code for a class with an eval method, send that to the Java compiler, and then load the resulting compiled class.
Use some scripting language that can be called from Java as an expression evaluator. Possibilities include Javascript1, BeanShell, and so on. A JSR 223 compliant scripting language implementation can be called via the Scripting API.
Write your own expression evaluator from scratch.
The first approach is probably simplest. The second and third approaches are a potential security risk if you get the expression to be evaluated from an untrusted user. (Think code injection.)
1 - Javascript in Java SE is a moving target. From Java 6, a version of Mozilla's Rhino Javascript implementation was bundled with Java SE. The in Java 8, it was superseded by Nashorn. In Java 11, Nashorn was deprecated, and finally dropped from the core codebase. As of 2021, both Rhino and Nashorn are being maintained as separate (non-Oracle) products, and Oracle's GraalVM has its own Javascript implementation.
There are very few real use cases in which being able to evaluate a String as a fragment of Java code is necessary or desirable. That is, asking how to do this is really an XY problem: you actually have a different problem, which can be solved a different way.
First ask yourself, where did this String that you wish to evaluate come from? Did another part of your program generate it, or was it input provided by the user?
Another part of my program generated it: so, you want one part of your program to decide the kind of operation to perform, but not perform the operation, and a second part that performs the chosen operation. Instead of generating and then evaluating a String, use the Strategy, Command or Builder design pattern, as appropriate for your particular case.
It is user input: the user could input anything, including commands that, when executed, could cause your program to misbehave, crash, expose information that should be secret, damage persistent information (such as the content of a database), and other such nastiness. The only way to prevent that would be to parse the String yourself, check it was not malicious, and then evaluate it. But parsing it yourself is much of the work that the requested evalfunction would do, so you have saved yourself nothing. Worse still, checking that arbitrary Java was not malicious is impossible, because checking that is the halting problem.
It is user input, but the syntax and semantics of permitted text to evaluate is greatly restricted: No general purpose facility can easily implement a general purpose parser and evaluator for whatever restricted syntax and semantics you have chosen. What you need to do is implement a parser and evaluator for your chosen syntax and semantics. If the task is simple, you could write a simple recursive-descent or finite-state-machine parser by hand. If the task is difficult, you could use a compiler-compiler (such as ANTLR) to do some of the work for you.
I just want to implement a desktop calculator!: A homework assignment, eh? If you could implement the evaluation of the input expression using a provided eval function, it would not be much of a homework assignment, would it? Your program would be three lines long. Your instructor probably expects you to write the code for a simple arithmetic parser/evaluator. There is well known algorithm, shunting-yard, which you might find useful.
With Java 9, we get access to jshell, so one can write something like this:
import jdk.jshell.JShell;
import java.lang.StringBuilder;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class Eval {
public static void main(String[] args) throws IOException {
try(JShell js = JShell.create(); BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
js.onSnippetEvent(snip -> {
if (snip.status() == jdk.jshell.Snippet.Status.VALID) {
System.out.println("➜ " + snip.value());
}
});
System.out.print("> ");
for (String line = br.readLine(); line != null; line = br.readLine()) {
js.eval(js.sourceCodeAnalysis().analyzeCompletion(line).source());
System.out.print("> ");
}
}
}
}
Sample run:
> 1 + 2 / 4 * 3
➜ 1
> 32 * 121
➜ 3872
> 4 * 5
➜ 20
> 121 * 51
➜ 6171
>
Slightly op, but that's what Java currently has to offer
I could advise you to use Exp4j. It is easy to understand as you can see from the following example code:
Expression e = new ExpressionBuilder("3 * sin(y) - 2 / (x - 2)")
.variables("x", "y")
.build()
.setVariable("x", 2.3)
.setVariable("y", 3.14);
double result = e.evaluate();
No, you can not have a generic "eval" in Java (or any compiled language). Unless you're willing to write a Java compiler AND a JVM to be executed inside of your Java program.
Yes, you can have some library to evaluate numeric algebraic expressions like the one above - see this thread for discussion.
As previous answers, there is no standard API in Java for this.
You can add groovy jar files to your path and groovy.util.Eval.me("4*5") gets your job done.
A fun way to solve your problem could be coding an eval() function on your own!
I've done it for you!
You can use FunctionSolver library simply by typing FunctionSolver.solveByX(function,value) inside your code. The function attribute is a String which represents the function you want to solve, the value attribute is the value of the independent variable
of your function (which MUST be x).
If you want to solve a function which contains more than one independent variable, you can use FunctionSolver.solve(function,values) where the values attribute is an HashMap(String,Double) which contains all your independent attributes (as Strings) and their respective values (as Doubles).
Another piece of information: I've coded a simple version of FunctionSolver, so its supports only Math methods which return a double value and which accepts one or two double values as fields (just use FunctionSolver.usableMathMethods() if you're curious) (These methods are: bs, sin, cos, tan, atan2, sqrt, log, log10, pow, exp, min, max, copySign, signum, IEEEremainder, acos, asin, atan, cbrt, ceil, cosh, expm1, floor, hypot, log1p, nextAfter, nextDown, nextUp, random, rint, sinh, tanh, toDegrees, toRadians, ulp). Also, that library supports the following operators: * / + - ^ (even if java normally does not support the ^ operator).
One last thing: while creating this library I had to use reflections to call Math methods. I think it's really cool, just have a look at this if you are interested in!
That's all, here it is the code (and the library):
package core;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
public abstract class FunctionSolver {
public static double solveNumericExpression (String expression) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
return solve(expression, new HashMap<>());
}
public static double solveByX (String function, double value) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
HashMap<String, Double> values = new HashMap<>();
values.put("x", value);
return solveComplexFunction(function, function, values);
}
public static double solve (String function, HashMap<String,Double> values) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
return solveComplexFunction(function, function, values);
}
private static double solveComplexFunction (String function, String motherFunction, HashMap<String, Double> values) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
int position = 0;
while(position < function.length()) {
if (alphabetic.contains(""+function.charAt(position))) {
if (position == 0 || !alphabetic.contains(""+function.charAt(position-1))) {
int endIndex = -1;
for (int j = position ; j < function.length()-1 ; j++) {
if (alphabetic.contains(""+function.charAt(j))
&& !alphabetic.contains(""+function.charAt(j+1))) {
endIndex = j;
break;
}
}
if (endIndex == -1 & alphabetic.contains(""+function.charAt(function.length()-1))) {
endIndex = function.length()-1;
}
if (endIndex != -1) {
String alphabeticElement = function.substring(position, endIndex+1);
if (Arrays.asList(usableMathMethods()).contains(alphabeticElement)) {
//Start analyzing a Math function
int closeParenthesisIndex = -1;
int openedParenthesisquantity = 0;
int commaIndex = -1;
for (int j = endIndex+1 ; j < function.length() ; j++) {
if (function.substring(j,j+1).equals("(")) {
openedParenthesisquantity++;
}else if (function.substring(j,j+1).equals(")")) {
openedParenthesisquantity--;
if (openedParenthesisquantity == 0) {
closeParenthesisIndex = j;
break;
}
}else if (function.substring(j,j+1).equals(",") & openedParenthesisquantity == 0) {
if (commaIndex == -1) {
commaIndex = j;
}else{
throw new IllegalArgumentException("The argument of math function (which is "+alphabeticElement+") has too many commas");
}
}
}
if (closeParenthesisIndex == -1) {
throw new IllegalArgumentException("The argument of a Math function (which is "+alphabeticElement+") hasn't got the closing bracket )");
}
String functionArgument = function.substring(endIndex+2,closeParenthesisIndex);
if (commaIndex != -1) {
double firstParameter = solveComplexFunction(functionArgument.substring(0,commaIndex),motherFunction,values);
double secondParameter = solveComplexFunction(functionArgument.substring(commaIndex+1),motherFunction,values);
Method mathMethod = Math.class.getDeclaredMethod(alphabeticElement, new Class<?>[] {double.class, double.class});
mathMethod.setAccessible(true);
String newKey = getNewKey(values);
values.put(newKey, (Double) mathMethod.invoke(null, firstParameter, secondParameter));
function = function.substring(0, position)+newKey
+((closeParenthesisIndex == function.length()-1)?(""):(function.substring(closeParenthesisIndex+1)));
}else {
double firstParameter = solveComplexFunction(functionArgument, motherFunction, values);
Method mathMethod = Math.class.getDeclaredMethod(alphabeticElement, new Class<?>[] {double.class});
mathMethod.setAccessible(true);
String newKey = getNewKey(values);
values.put(newKey, (Double) mathMethod.invoke(null, firstParameter));
function = function.substring(0, position)+newKey
+((closeParenthesisIndex == function.length()-1)?(""):(function.substring(closeParenthesisIndex+1)));
}
}else if (!values.containsKey(alphabeticElement)) {
throw new IllegalArgumentException("Found a group of letters ("+alphabeticElement+") which is neither a variable nor a Math function: ");
}
}
}
}
position++;
}
return solveBracketsFunction(function,motherFunction,values);
}
private static double solveBracketsFunction (String function,String motherFunction,HashMap<String, Double> values) throws IllegalArgumentException{
function = function.replace(" ", "");
String openingBrackets = "([{";
String closingBrackets = ")]}";
int parenthesisIndex = 0;
do {
int position = 0;
int openParenthesisBlockIndex = -1;
String currentOpeningBracket = openingBrackets.charAt(parenthesisIndex)+"";
String currentClosingBracket = closingBrackets.charAt(parenthesisIndex)+"";
if (contOccouranceIn(currentOpeningBracket,function) != contOccouranceIn(currentClosingBracket,function)) {
throw new IllegalArgumentException("Error: brackets are misused in the function "+function);
}
while (position < function.length()) {
if (function.substring(position,position+1).equals(currentOpeningBracket)) {
if (position != 0 && !operators.contains(function.substring(position-1,position))) {
throw new IllegalArgumentException("Error in function: there must be an operator following a "+currentClosingBracket+" breacket");
}
openParenthesisBlockIndex = position;
}else if (function.substring(position,position+1).equals(currentClosingBracket)) {
if (position != function.length()-1 && !operators.contains(function.substring(position+1,position+2))) {
throw new IllegalArgumentException("Error in function: there must be an operator before a "+currentClosingBracket+" breacket");
}
String newKey = getNewKey(values);
values.put(newKey, solveBracketsFunction(function.substring(openParenthesisBlockIndex+1,position),motherFunction, values));
function = function.substring(0,openParenthesisBlockIndex)+newKey
+((position == function.length()-1)?(""):(function.substring(position+1)));
position = -1;
}
position++;
}
parenthesisIndex++;
}while (parenthesisIndex < openingBrackets.length());
return solveBasicFunction(function,motherFunction, values);
}
private static double solveBasicFunction (String function, String motherFunction, HashMap<String, Double> values) throws IllegalArgumentException{
if (!firstContainsOnlySecond(function, alphanumeric+operators)) {
throw new IllegalArgumentException("The function "+function+" is not a basic function");
}
if (function.contains("**") |
function.contains("//") |
function.contains("--") |
function.contains("+*") |
function.contains("+/") |
function.contains("-*") |
function.contains("-/")) {
/*
* ( -+ , +- , *- , *+ , /- , /+ )> Those values are admitted
*/
throw new IllegalArgumentException("Operators are misused in the function");
}
function = function.replace(" ", "");
int position;
int operatorIndex = 0;
String currentOperator;
do {
currentOperator = operators.substring(operatorIndex,operatorIndex+1);
if (currentOperator.equals("*")) {
currentOperator+="/";
operatorIndex++;
}else if (currentOperator.equals("+")) {
currentOperator+="-";
operatorIndex++;
}
operatorIndex++;
position = 0;
while (position < function.length()) {
if ((position == 0 && !(""+function.charAt(position)).equals("-") && !(""+function.charAt(position)).equals("+") && operators.contains(""+function.charAt(position))) ||
(position == function.length()-1 && operators.contains(""+function.charAt(position)))){
throw new IllegalArgumentException("Operators are misused in the function");
}
if (currentOperator.contains(function.substring(position, position+1)) & position != 0) {
int firstTermBeginIndex = position;
while (firstTermBeginIndex > 0) {
if ((alphanumeric.contains(""+function.charAt(firstTermBeginIndex))) & (operators.contains(""+function.charAt(firstTermBeginIndex-1)))){
break;
}
firstTermBeginIndex--;
}
if (firstTermBeginIndex != 0 && (function.charAt(firstTermBeginIndex-1) == '-' | function.charAt(firstTermBeginIndex-1) == '+')) {
if (firstTermBeginIndex == 1) {
firstTermBeginIndex--;
}else if (operators.contains(""+(function.charAt(firstTermBeginIndex-2)))){
firstTermBeginIndex--;
}
}
String firstTerm = function.substring(firstTermBeginIndex,position);
int secondTermLastIndex = position;
while (secondTermLastIndex < function.length()-1) {
if ((alphanumeric.contains(""+function.charAt(secondTermLastIndex))) & (operators.contains(""+function.charAt(secondTermLastIndex+1)))) {
break;
}
secondTermLastIndex++;
}
String secondTerm = function.substring(position+1,secondTermLastIndex+1);
double result;
switch (function.substring(position,position+1)) {
case "*": result = solveSingleValue(firstTerm,values)*solveSingleValue(secondTerm,values); break;
case "/": result = solveSingleValue(firstTerm,values)/solveSingleValue(secondTerm,values); break;
case "+": result = solveSingleValue(firstTerm,values)+solveSingleValue(secondTerm,values); break;
case "-": result = solveSingleValue(firstTerm,values)-solveSingleValue(secondTerm,values); break;
case "^": result = Math.pow(solveSingleValue(firstTerm,values),solveSingleValue(secondTerm,values)); break;
default: throw new IllegalArgumentException("Unknown operator: "+currentOperator);
}
String newAttribute = getNewKey(values);
values.put(newAttribute, result);
function = function.substring(0,firstTermBeginIndex)+newAttribute+function.substring(secondTermLastIndex+1,function.length());
deleteValueIfPossible(firstTerm, values, motherFunction);
deleteValueIfPossible(secondTerm, values, motherFunction);
position = -1;
}
position++;
}
}while (operatorIndex < operators.length());
return solveSingleValue(function, values);
}
private static double solveSingleValue (String singleValue, HashMap<String, Double> values) throws IllegalArgumentException{
if (isDouble(singleValue)) {
return Double.parseDouble(singleValue);
}else if (firstContainsOnlySecond(singleValue, alphabetic)){
return getValueFromVariable(singleValue, values);
}else if (firstContainsOnlySecond(singleValue, alphanumeric+"-+")) {
String[] composition = splitByLettersAndNumbers(singleValue);
if (composition.length != 2) {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}else {
if (composition[0].equals("-")) {
composition[0] = "-1";
}else if (composition[1].equals("-")) {
composition[1] = "-1";
}else if (composition[0].equals("+")) {
composition[0] = "+1";
}else if (composition[1].equals("+")) {
composition[1] = "+1";
}
if (isDouble(composition[0])) {
return Double.parseDouble(composition[0])*getValueFromVariable(composition[1], values);
}else if (isDouble(composition[1])){
return Double.parseDouble(composition[1])*getValueFromVariable(composition[0], values);
}else {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}
}
}else {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}
}
private static double getValueFromVariable (String variable, HashMap<String, Double> values) throws IllegalArgumentException{
Double val = values.get(variable);
if (val == null) {
throw new IllegalArgumentException("Unknown variable: "+variable);
}else {
return val;
}
}
/*
* FunctionSolver help tools:
*
*/
private static final String alphabetic = "abcdefghilmnopqrstuvzwykxy";
private static final String numeric = "0123456789.";
private static final String alphanumeric = alphabetic+numeric;
private static final String operators = "^*/+-"; //--> Operators order in important!
private static boolean firstContainsOnlySecond(String firstString, String secondString) {
for (int j = 0 ; j < firstString.length() ; j++) {
if (!secondString.contains(firstString.substring(j, j+1))) {
return false;
}
}
return true;
}
private static String getNewKey (HashMap<String, Double> hashMap) {
String alpha = "abcdefghilmnopqrstuvzyjkx";
for (int j = 0 ; j < alpha.length() ; j++) {
String k = alpha.substring(j,j+1);
if (!hashMap.containsKey(k) & !Arrays.asList(usableMathMethods()).contains(k)) {
return k;
}
}
for (int j = 0 ; j < alpha.length() ; j++) {
for (int i = 0 ; i < alpha.length() ; i++) {
String k = alpha.substring(j,j+1)+alpha.substring(i,i+1);
if (!hashMap.containsKey(k) & !Arrays.asList(usableMathMethods()).contains(k)) {
return k;
}
}
}
throw new NullPointerException();
}
public static String[] usableMathMethods () {
/*
* Only methods that:
* return a double type
* present one or two parameters (which are double type)
*/
Method[] mathMethods = Math.class.getDeclaredMethods();
ArrayList<String> usableMethodsNames = new ArrayList<>();
for (Method method : mathMethods) {
boolean usable = true;
int argumentsCounter = 0;
Class<?>[] methodParametersTypes = method.getParameterTypes();
for (Class<?> parameter : methodParametersTypes) {
if (!parameter.getSimpleName().equalsIgnoreCase("double")) {
usable = false;
break;
}else {
argumentsCounter++;
}
}
if (!method.getReturnType().getSimpleName().toLowerCase().equals("double")) {
usable = false;
}
if (usable & argumentsCounter<=2) {
usableMethodsNames.add(method.getName());
}
}
return usableMethodsNames.toArray(new String[usableMethodsNames.size()]);
}
private static boolean isDouble (String number) {
try {
Double.parseDouble(number);
return true;
}catch (Exception ex) {
return false;
}
}
private static String[] splitByLettersAndNumbers (String val) {
if (!firstContainsOnlySecond(val, alphanumeric+"+-")) {
throw new IllegalArgumentException("Wrong passed value: <<"+val+">>");
}
ArrayList<String> response = new ArrayList<>();
String searchingFor;
int lastIndex = 0;
if (firstContainsOnlySecond(""+val.charAt(0), numeric+"+-")) {
searchingFor = alphabetic;
}else {
searchingFor = numeric+"+-";
}
for (int j = 0 ; j < val.length() ; j++) {
if (searchingFor.contains(val.charAt(j)+"")) {
response.add(val.substring(lastIndex, j));
lastIndex = j;
if (searchingFor.equals(numeric+"+-")) {
searchingFor = alphabetic;
}else {
searchingFor = numeric+"+-";
}
}
}
response.add(val.substring(lastIndex,val.length()));
return response.toArray(new String[response.size()]);
}
private static void deleteValueIfPossible (String val, HashMap<String, Double> values, String function) {
if (values.get(val) != null & function != null) {
if (!function.contains(val)) {
values.remove(val);
}
}
}
private static int contOccouranceIn (String howManyOfThatString, String inThatString) {
return inThatString.length() - inThatString.replace(howManyOfThatString, "").length();
}
}
Writing your own library is not that hard as u might thing. Here is link for Shunting-yard algorithm with step by step algorithm explenation. Although, you will have to parse the input for tokens first.
There are 2 other questions wich can give you some information too:
Turn a String into a Math Expression?
What's a good library for parsing mathematical expressions in java?
As there are many answers, I'm adding my implementation on top of eval() method with some additional features like support for factorial, evaluating complex expressions etc.
package evaluation;
import java.math.BigInteger;
import java.util.EmptyStackException;
import java.util.Scanner;
import java.util.Stack;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
public class EvalPlus {
private static Scanner scanner = new Scanner(System.in);
public static void main(String[] args) {
System.out.println("This Evaluation is based on BODMAS rule\n");
evaluate();
}
private static void evaluate() {
StringBuilder finalStr = new StringBuilder();
System.out.println("Enter an expression to evaluate:");
String expr = scanner.nextLine();
if(isProperExpression(expr)) {
expr = replaceBefore(expr);
char[] temp = expr.toCharArray();
String operators = "(+-*/%)";
for(int i = 0; i < temp.length; i++) {
if((i == 0 && temp[i] != '*') || (i == temp.length-1 && temp[i] != '*' && temp[i] != '!')) {
finalStr.append(temp[i]);
} else if((i > 0 && i < temp.length -1) || (i==temp.length-1 && temp[i] == '!')) {
if(temp[i] == '!') {
StringBuilder str = new StringBuilder();
for(int k = i-1; k >= 0; k--) {
if(Character.isDigit(temp[k])) {
str.insert(0, temp[k] );
} else {
break;
}
}
Long prev = Long.valueOf(str.toString());
BigInteger val = new BigInteger("1");
for(Long j = prev; j > 1; j--) {
val = val.multiply(BigInteger.valueOf(j));
}
finalStr.setLength(finalStr.length() - str.length());
finalStr.append("(" + val + ")");
if(temp.length > i+1) {
char next = temp[i+1];
if(operators.indexOf(next) == -1) {
finalStr.append("*");
}
}
} else {
finalStr.append(temp[i]);
}
}
}
expr = finalStr.toString();
if(expr != null && !expr.isEmpty()) {
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
try {
System.out.println("Result: " + engine.eval(expr));
evaluate();
} catch (ScriptException e) {
System.out.println(e.getMessage());
}
} else {
System.out.println("Please give an expression");
evaluate();
}
} else {
System.out.println("Not a valid expression");
evaluate();
}
}
private static String replaceBefore(String expr) {
expr = expr.replace("(", "*(");
expr = expr.replace("+*", "+").replace("-*", "-").replace("**", "*").replace("/*", "/").replace("%*", "%");
return expr;
}
private static boolean isProperExpression(String expr) {
expr = expr.replaceAll("[^()]", "");
char[] arr = expr.toCharArray();
Stack<Character> stack = new Stack<Character>();
int i =0;
while(i < arr.length) {
try {
if(arr[i] == '(') {
stack.push(arr[i]);
} else {
stack.pop();
}
} catch (EmptyStackException e) {
stack.push(arr[i]);
}
i++;
}
return stack.isEmpty();
}
}
Please find the updated gist anytime here. Also comment if any issues are there. Thanks.
There are some perfectly capable answers here. However for non-trivial script it may be desirable to retain the code in a cache, or for debugging purposes, or even to have dynamically self-updating code.
To that end, sometimes it's simpler or more robust to interact with Java via command line. Create a temporary directory, output your script and any assets, create the jar. Finally import your new code.
It's a bit beyond the scope of normal eval() use in most languages, though you could certainly implement eval by returning the result from some function in your jar.
Still, thought I'd mention this method as it does fully encapsulate everything Java can do without 3rd party tools, in case of desperation. This method allows me to turn HTML templates into objects and save them, avoiding the need to parse a template at runtime.
import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;
class Calculate {
public static void main(String[] args) {
String strng = "8*-2*3*-1*10/2+6-2";
String[] oparator = {"+","-","*","/"};
List<String> op1 = new ArrayList<>();
String[] x = strng.split("");
int sayac=0;
for (String i : x) {
sayac ++;
for (String c : oparator) {
if (i.equals(c)) {
try {
int j = Integer.parseInt(strng.substring(0, sayac - 1));
op1.add(strng.substring(0, sayac - 1));
op1.add(c);
strng = strng.substring(sayac);
sayac = 0;
}catch (Exception e)
{
continue;
}
}
}
}
op1.add(strng);
ListIterator<String> it = op1.listIterator();
List<List> newlist = new ArrayList<>() ;
while (it.hasNext()) {
List<String> p= new ArrayList<>();
p.add(String.valueOf(it.nextIndex()));
p.add(it.next());
newlist.add(p);
}
int sayac2=0;
String oparatorvalue = "*";
calculate(sayac2,newlist,oparatorvalue);
String oparatorvalue2 = "/";
calculate(sayac2,newlist,oparatorvalue2);
String oparatorvalue3 = "+";
calculate(sayac2,newlist,oparatorvalue3);
String oparatorvalue4 = "-";
calculate(sayac2,newlist,oparatorvalue4);
System.out.println("Result:"+newlist.get(0).get(1));
}
private static void calculate(int sayac2, List<List> newlist, String oparatorvalue) {
while (sayac2<4){
try{
for (List j : newlist) {
if (j.get(1) == oparatorvalue) {
Integer opindex = newlist.indexOf(j);
Object sayi1 = newlist.get(opindex - 1).get(1);
Object sayi2 = newlist.get(opindex + 1).get(1);
int sonuc=0;
if (oparatorvalue.equals("*")){
sonuc = Integer.parseInt(sayi1.toString()) * Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("/")){
sonuc = Integer.parseInt(sayi1.toString()) / Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("+")){
sonuc = Integer.parseInt(sayi1.toString()) + Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("-")){
sonuc = Integer.parseInt(sayi1.toString()) - Integer.parseInt(sayi2.toString());
}
newlist.remove(opindex - 1);
newlist.remove(opindex - 1);
newlist.remove(opindex - 1);
List<String> sonuclist = new ArrayList<>();
sonuclist.add(String.valueOf(opindex - 1));
sonuclist.add(String.valueOf(sonuc));
newlist.add(opindex - 1, sonuclist);
}}}
catch (Exception e){
continue;
}
sayac2++;}
}
}
If you do not want to import heavy scripting library, you can use SimpleExpressionEvaluator directly into your code
Usage:
Expression.eval("1+2").asString(); // returns "3.0"
Expression.eval("1+2").asInt(); // returns 3
Expression.eval("2>3").asString(); // returns "false"
Expression.eval("2>3").asBoolean(); // returns false
Expression.eval("(3>2)||((2<4)&&(2>1))").asString(); // returns "true"
With variables:
HashMap<String, Object> st = new HashMap<String, Object>();
st.put("a",1);
st.put("b",2);
st.put("c",3);
st.put("d",4);
Expression.eval("a+b", st).asInt(); // or simply asString()
Expression.eval("a>b",st).asBoolean(); // or simply asString()
Expression.eval("(c>b)||((b<d)&&(b>a))",st).asBoolean(); // or simply asString()
Expression.eval("(c>2)||((2<d)&&(b>1))",st).asBoolean(); // or simply asString()
Using ExpressionBuilder:
Expression.expressionBuilder().putSymbol("a",2).putSymbol("b",3).build("(b>a)").evaluate()
The following resolved the issue:
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
String str = "4*5";
System.out.println(engine.eval(str));
I have a string like the following:
String str = "4*5";
Now I have to get the result of 20 by using the string.
I know in some other languages the eval() function will do this.
How can I do this in Java?
You can use the ScriptEngine class and evaluate it as a Javascript string.
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");
Object result = engine.eval("4*5");
There may be a better way, but this one works.
There is no standard Java class or method that will do what you want. Your options include:
Select and use some third-party expression evaluation library. For example JEL or any of the half dozen libraries listed here.
Wrap the expression in the Java source code for a class with an eval method, send that to the Java compiler, and then load the resulting compiled class.
Use some scripting language that can be called from Java as an expression evaluator. Possibilities include Javascript1, BeanShell, and so on. A JSR 223 compliant scripting language implementation can be called via the Scripting API.
Write your own expression evaluator from scratch.
The first approach is probably simplest. The second and third approaches are a potential security risk if you get the expression to be evaluated from an untrusted user. (Think code injection.)
1 - Javascript in Java SE is a moving target. From Java 6, a version of Mozilla's Rhino Javascript implementation was bundled with Java SE. The in Java 8, it was superseded by Nashorn. In Java 11, Nashorn was deprecated, and finally dropped from the core codebase. As of 2021, both Rhino and Nashorn are being maintained as separate (non-Oracle) products, and Oracle's GraalVM has its own Javascript implementation.
There are very few real use cases in which being able to evaluate a String as a fragment of Java code is necessary or desirable. That is, asking how to do this is really an XY problem: you actually have a different problem, which can be solved a different way.
First ask yourself, where did this String that you wish to evaluate come from? Did another part of your program generate it, or was it input provided by the user?
Another part of my program generated it: so, you want one part of your program to decide the kind of operation to perform, but not perform the operation, and a second part that performs the chosen operation. Instead of generating and then evaluating a String, use the Strategy, Command or Builder design pattern, as appropriate for your particular case.
It is user input: the user could input anything, including commands that, when executed, could cause your program to misbehave, crash, expose information that should be secret, damage persistent information (such as the content of a database), and other such nastiness. The only way to prevent that would be to parse the String yourself, check it was not malicious, and then evaluate it. But parsing it yourself is much of the work that the requested evalfunction would do, so you have saved yourself nothing. Worse still, checking that arbitrary Java was not malicious is impossible, because checking that is the halting problem.
It is user input, but the syntax and semantics of permitted text to evaluate is greatly restricted: No general purpose facility can easily implement a general purpose parser and evaluator for whatever restricted syntax and semantics you have chosen. What you need to do is implement a parser and evaluator for your chosen syntax and semantics. If the task is simple, you could write a simple recursive-descent or finite-state-machine parser by hand. If the task is difficult, you could use a compiler-compiler (such as ANTLR) to do some of the work for you.
I just want to implement a desktop calculator!: A homework assignment, eh? If you could implement the evaluation of the input expression using a provided eval function, it would not be much of a homework assignment, would it? Your program would be three lines long. Your instructor probably expects you to write the code for a simple arithmetic parser/evaluator. There is well known algorithm, shunting-yard, which you might find useful.
With Java 9, we get access to jshell, so one can write something like this:
import jdk.jshell.JShell;
import java.lang.StringBuilder;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class Eval {
public static void main(String[] args) throws IOException {
try(JShell js = JShell.create(); BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
js.onSnippetEvent(snip -> {
if (snip.status() == jdk.jshell.Snippet.Status.VALID) {
System.out.println("➜ " + snip.value());
}
});
System.out.print("> ");
for (String line = br.readLine(); line != null; line = br.readLine()) {
js.eval(js.sourceCodeAnalysis().analyzeCompletion(line).source());
System.out.print("> ");
}
}
}
}
Sample run:
> 1 + 2 / 4 * 3
➜ 1
> 32 * 121
➜ 3872
> 4 * 5
➜ 20
> 121 * 51
➜ 6171
>
Slightly op, but that's what Java currently has to offer
I could advise you to use Exp4j. It is easy to understand as you can see from the following example code:
Expression e = new ExpressionBuilder("3 * sin(y) - 2 / (x - 2)")
.variables("x", "y")
.build()
.setVariable("x", 2.3)
.setVariable("y", 3.14);
double result = e.evaluate();
No, you can not have a generic "eval" in Java (or any compiled language). Unless you're willing to write a Java compiler AND a JVM to be executed inside of your Java program.
Yes, you can have some library to evaluate numeric algebraic expressions like the one above - see this thread for discussion.
As previous answers, there is no standard API in Java for this.
You can add groovy jar files to your path and groovy.util.Eval.me("4*5") gets your job done.
A fun way to solve your problem could be coding an eval() function on your own!
I've done it for you!
You can use FunctionSolver library simply by typing FunctionSolver.solveByX(function,value) inside your code. The function attribute is a String which represents the function you want to solve, the value attribute is the value of the independent variable
of your function (which MUST be x).
If you want to solve a function which contains more than one independent variable, you can use FunctionSolver.solve(function,values) where the values attribute is an HashMap(String,Double) which contains all your independent attributes (as Strings) and their respective values (as Doubles).
Another piece of information: I've coded a simple version of FunctionSolver, so its supports only Math methods which return a double value and which accepts one or two double values as fields (just use FunctionSolver.usableMathMethods() if you're curious) (These methods are: bs, sin, cos, tan, atan2, sqrt, log, log10, pow, exp, min, max, copySign, signum, IEEEremainder, acos, asin, atan, cbrt, ceil, cosh, expm1, floor, hypot, log1p, nextAfter, nextDown, nextUp, random, rint, sinh, tanh, toDegrees, toRadians, ulp). Also, that library supports the following operators: * / + - ^ (even if java normally does not support the ^ operator).
One last thing: while creating this library I had to use reflections to call Math methods. I think it's really cool, just have a look at this if you are interested in!
That's all, here it is the code (and the library):
package core;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
public abstract class FunctionSolver {
public static double solveNumericExpression (String expression) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
return solve(expression, new HashMap<>());
}
public static double solveByX (String function, double value) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
HashMap<String, Double> values = new HashMap<>();
values.put("x", value);
return solveComplexFunction(function, function, values);
}
public static double solve (String function, HashMap<String,Double> values) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
return solveComplexFunction(function, function, values);
}
private static double solveComplexFunction (String function, String motherFunction, HashMap<String, Double> values) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
int position = 0;
while(position < function.length()) {
if (alphabetic.contains(""+function.charAt(position))) {
if (position == 0 || !alphabetic.contains(""+function.charAt(position-1))) {
int endIndex = -1;
for (int j = position ; j < function.length()-1 ; j++) {
if (alphabetic.contains(""+function.charAt(j))
&& !alphabetic.contains(""+function.charAt(j+1))) {
endIndex = j;
break;
}
}
if (endIndex == -1 & alphabetic.contains(""+function.charAt(function.length()-1))) {
endIndex = function.length()-1;
}
if (endIndex != -1) {
String alphabeticElement = function.substring(position, endIndex+1);
if (Arrays.asList(usableMathMethods()).contains(alphabeticElement)) {
//Start analyzing a Math function
int closeParenthesisIndex = -1;
int openedParenthesisquantity = 0;
int commaIndex = -1;
for (int j = endIndex+1 ; j < function.length() ; j++) {
if (function.substring(j,j+1).equals("(")) {
openedParenthesisquantity++;
}else if (function.substring(j,j+1).equals(")")) {
openedParenthesisquantity--;
if (openedParenthesisquantity == 0) {
closeParenthesisIndex = j;
break;
}
}else if (function.substring(j,j+1).equals(",") & openedParenthesisquantity == 0) {
if (commaIndex == -1) {
commaIndex = j;
}else{
throw new IllegalArgumentException("The argument of math function (which is "+alphabeticElement+") has too many commas");
}
}
}
if (closeParenthesisIndex == -1) {
throw new IllegalArgumentException("The argument of a Math function (which is "+alphabeticElement+") hasn't got the closing bracket )");
}
String functionArgument = function.substring(endIndex+2,closeParenthesisIndex);
if (commaIndex != -1) {
double firstParameter = solveComplexFunction(functionArgument.substring(0,commaIndex),motherFunction,values);
double secondParameter = solveComplexFunction(functionArgument.substring(commaIndex+1),motherFunction,values);
Method mathMethod = Math.class.getDeclaredMethod(alphabeticElement, new Class<?>[] {double.class, double.class});
mathMethod.setAccessible(true);
String newKey = getNewKey(values);
values.put(newKey, (Double) mathMethod.invoke(null, firstParameter, secondParameter));
function = function.substring(0, position)+newKey
+((closeParenthesisIndex == function.length()-1)?(""):(function.substring(closeParenthesisIndex+1)));
}else {
double firstParameter = solveComplexFunction(functionArgument, motherFunction, values);
Method mathMethod = Math.class.getDeclaredMethod(alphabeticElement, new Class<?>[] {double.class});
mathMethod.setAccessible(true);
String newKey = getNewKey(values);
values.put(newKey, (Double) mathMethod.invoke(null, firstParameter));
function = function.substring(0, position)+newKey
+((closeParenthesisIndex == function.length()-1)?(""):(function.substring(closeParenthesisIndex+1)));
}
}else if (!values.containsKey(alphabeticElement)) {
throw new IllegalArgumentException("Found a group of letters ("+alphabeticElement+") which is neither a variable nor a Math function: ");
}
}
}
}
position++;
}
return solveBracketsFunction(function,motherFunction,values);
}
private static double solveBracketsFunction (String function,String motherFunction,HashMap<String, Double> values) throws IllegalArgumentException{
function = function.replace(" ", "");
String openingBrackets = "([{";
String closingBrackets = ")]}";
int parenthesisIndex = 0;
do {
int position = 0;
int openParenthesisBlockIndex = -1;
String currentOpeningBracket = openingBrackets.charAt(parenthesisIndex)+"";
String currentClosingBracket = closingBrackets.charAt(parenthesisIndex)+"";
if (contOccouranceIn(currentOpeningBracket,function) != contOccouranceIn(currentClosingBracket,function)) {
throw new IllegalArgumentException("Error: brackets are misused in the function "+function);
}
while (position < function.length()) {
if (function.substring(position,position+1).equals(currentOpeningBracket)) {
if (position != 0 && !operators.contains(function.substring(position-1,position))) {
throw new IllegalArgumentException("Error in function: there must be an operator following a "+currentClosingBracket+" breacket");
}
openParenthesisBlockIndex = position;
}else if (function.substring(position,position+1).equals(currentClosingBracket)) {
if (position != function.length()-1 && !operators.contains(function.substring(position+1,position+2))) {
throw new IllegalArgumentException("Error in function: there must be an operator before a "+currentClosingBracket+" breacket");
}
String newKey = getNewKey(values);
values.put(newKey, solveBracketsFunction(function.substring(openParenthesisBlockIndex+1,position),motherFunction, values));
function = function.substring(0,openParenthesisBlockIndex)+newKey
+((position == function.length()-1)?(""):(function.substring(position+1)));
position = -1;
}
position++;
}
parenthesisIndex++;
}while (parenthesisIndex < openingBrackets.length());
return solveBasicFunction(function,motherFunction, values);
}
private static double solveBasicFunction (String function, String motherFunction, HashMap<String, Double> values) throws IllegalArgumentException{
if (!firstContainsOnlySecond(function, alphanumeric+operators)) {
throw new IllegalArgumentException("The function "+function+" is not a basic function");
}
if (function.contains("**") |
function.contains("//") |
function.contains("--") |
function.contains("+*") |
function.contains("+/") |
function.contains("-*") |
function.contains("-/")) {
/*
* ( -+ , +- , *- , *+ , /- , /+ )> Those values are admitted
*/
throw new IllegalArgumentException("Operators are misused in the function");
}
function = function.replace(" ", "");
int position;
int operatorIndex = 0;
String currentOperator;
do {
currentOperator = operators.substring(operatorIndex,operatorIndex+1);
if (currentOperator.equals("*")) {
currentOperator+="/";
operatorIndex++;
}else if (currentOperator.equals("+")) {
currentOperator+="-";
operatorIndex++;
}
operatorIndex++;
position = 0;
while (position < function.length()) {
if ((position == 0 && !(""+function.charAt(position)).equals("-") && !(""+function.charAt(position)).equals("+") && operators.contains(""+function.charAt(position))) ||
(position == function.length()-1 && operators.contains(""+function.charAt(position)))){
throw new IllegalArgumentException("Operators are misused in the function");
}
if (currentOperator.contains(function.substring(position, position+1)) & position != 0) {
int firstTermBeginIndex = position;
while (firstTermBeginIndex > 0) {
if ((alphanumeric.contains(""+function.charAt(firstTermBeginIndex))) & (operators.contains(""+function.charAt(firstTermBeginIndex-1)))){
break;
}
firstTermBeginIndex--;
}
if (firstTermBeginIndex != 0 && (function.charAt(firstTermBeginIndex-1) == '-' | function.charAt(firstTermBeginIndex-1) == '+')) {
if (firstTermBeginIndex == 1) {
firstTermBeginIndex--;
}else if (operators.contains(""+(function.charAt(firstTermBeginIndex-2)))){
firstTermBeginIndex--;
}
}
String firstTerm = function.substring(firstTermBeginIndex,position);
int secondTermLastIndex = position;
while (secondTermLastIndex < function.length()-1) {
if ((alphanumeric.contains(""+function.charAt(secondTermLastIndex))) & (operators.contains(""+function.charAt(secondTermLastIndex+1)))) {
break;
}
secondTermLastIndex++;
}
String secondTerm = function.substring(position+1,secondTermLastIndex+1);
double result;
switch (function.substring(position,position+1)) {
case "*": result = solveSingleValue(firstTerm,values)*solveSingleValue(secondTerm,values); break;
case "/": result = solveSingleValue(firstTerm,values)/solveSingleValue(secondTerm,values); break;
case "+": result = solveSingleValue(firstTerm,values)+solveSingleValue(secondTerm,values); break;
case "-": result = solveSingleValue(firstTerm,values)-solveSingleValue(secondTerm,values); break;
case "^": result = Math.pow(solveSingleValue(firstTerm,values),solveSingleValue(secondTerm,values)); break;
default: throw new IllegalArgumentException("Unknown operator: "+currentOperator);
}
String newAttribute = getNewKey(values);
values.put(newAttribute, result);
function = function.substring(0,firstTermBeginIndex)+newAttribute+function.substring(secondTermLastIndex+1,function.length());
deleteValueIfPossible(firstTerm, values, motherFunction);
deleteValueIfPossible(secondTerm, values, motherFunction);
position = -1;
}
position++;
}
}while (operatorIndex < operators.length());
return solveSingleValue(function, values);
}
private static double solveSingleValue (String singleValue, HashMap<String, Double> values) throws IllegalArgumentException{
if (isDouble(singleValue)) {
return Double.parseDouble(singleValue);
}else if (firstContainsOnlySecond(singleValue, alphabetic)){
return getValueFromVariable(singleValue, values);
}else if (firstContainsOnlySecond(singleValue, alphanumeric+"-+")) {
String[] composition = splitByLettersAndNumbers(singleValue);
if (composition.length != 2) {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}else {
if (composition[0].equals("-")) {
composition[0] = "-1";
}else if (composition[1].equals("-")) {
composition[1] = "-1";
}else if (composition[0].equals("+")) {
composition[0] = "+1";
}else if (composition[1].equals("+")) {
composition[1] = "+1";
}
if (isDouble(composition[0])) {
return Double.parseDouble(composition[0])*getValueFromVariable(composition[1], values);
}else if (isDouble(composition[1])){
return Double.parseDouble(composition[1])*getValueFromVariable(composition[0], values);
}else {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}
}
}else {
throw new IllegalArgumentException("Wrong expression: "+singleValue);
}
}
private static double getValueFromVariable (String variable, HashMap<String, Double> values) throws IllegalArgumentException{
Double val = values.get(variable);
if (val == null) {
throw new IllegalArgumentException("Unknown variable: "+variable);
}else {
return val;
}
}
/*
* FunctionSolver help tools:
*
*/
private static final String alphabetic = "abcdefghilmnopqrstuvzwykxy";
private static final String numeric = "0123456789.";
private static final String alphanumeric = alphabetic+numeric;
private static final String operators = "^*/+-"; //--> Operators order in important!
private static boolean firstContainsOnlySecond(String firstString, String secondString) {
for (int j = 0 ; j < firstString.length() ; j++) {
if (!secondString.contains(firstString.substring(j, j+1))) {
return false;
}
}
return true;
}
private static String getNewKey (HashMap<String, Double> hashMap) {
String alpha = "abcdefghilmnopqrstuvzyjkx";
for (int j = 0 ; j < alpha.length() ; j++) {
String k = alpha.substring(j,j+1);
if (!hashMap.containsKey(k) & !Arrays.asList(usableMathMethods()).contains(k)) {
return k;
}
}
for (int j = 0 ; j < alpha.length() ; j++) {
for (int i = 0 ; i < alpha.length() ; i++) {
String k = alpha.substring(j,j+1)+alpha.substring(i,i+1);
if (!hashMap.containsKey(k) & !Arrays.asList(usableMathMethods()).contains(k)) {
return k;
}
}
}
throw new NullPointerException();
}
public static String[] usableMathMethods () {
/*
* Only methods that:
* return a double type
* present one or two parameters (which are double type)
*/
Method[] mathMethods = Math.class.getDeclaredMethods();
ArrayList<String> usableMethodsNames = new ArrayList<>();
for (Method method : mathMethods) {
boolean usable = true;
int argumentsCounter = 0;
Class<?>[] methodParametersTypes = method.getParameterTypes();
for (Class<?> parameter : methodParametersTypes) {
if (!parameter.getSimpleName().equalsIgnoreCase("double")) {
usable = false;
break;
}else {
argumentsCounter++;
}
}
if (!method.getReturnType().getSimpleName().toLowerCase().equals("double")) {
usable = false;
}
if (usable & argumentsCounter<=2) {
usableMethodsNames.add(method.getName());
}
}
return usableMethodsNames.toArray(new String[usableMethodsNames.size()]);
}
private static boolean isDouble (String number) {
try {
Double.parseDouble(number);
return true;
}catch (Exception ex) {
return false;
}
}
private static String[] splitByLettersAndNumbers (String val) {
if (!firstContainsOnlySecond(val, alphanumeric+"+-")) {
throw new IllegalArgumentException("Wrong passed value: <<"+val+">>");
}
ArrayList<String> response = new ArrayList<>();
String searchingFor;
int lastIndex = 0;
if (firstContainsOnlySecond(""+val.charAt(0), numeric+"+-")) {
searchingFor = alphabetic;
}else {
searchingFor = numeric+"+-";
}
for (int j = 0 ; j < val.length() ; j++) {
if (searchingFor.contains(val.charAt(j)+"")) {
response.add(val.substring(lastIndex, j));
lastIndex = j;
if (searchingFor.equals(numeric+"+-")) {
searchingFor = alphabetic;
}else {
searchingFor = numeric+"+-";
}
}
}
response.add(val.substring(lastIndex,val.length()));
return response.toArray(new String[response.size()]);
}
private static void deleteValueIfPossible (String val, HashMap<String, Double> values, String function) {
if (values.get(val) != null & function != null) {
if (!function.contains(val)) {
values.remove(val);
}
}
}
private static int contOccouranceIn (String howManyOfThatString, String inThatString) {
return inThatString.length() - inThatString.replace(howManyOfThatString, "").length();
}
}
Writing your own library is not that hard as u might thing. Here is link for Shunting-yard algorithm with step by step algorithm explenation. Although, you will have to parse the input for tokens first.
There are 2 other questions wich can give you some information too:
Turn a String into a Math Expression?
What's a good library for parsing mathematical expressions in java?
As there are many answers, I'm adding my implementation on top of eval() method with some additional features like support for factorial, evaluating complex expressions etc.
package evaluation;
import java.math.BigInteger;
import java.util.EmptyStackException;
import java.util.Scanner;
import java.util.Stack;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
public class EvalPlus {
private static Scanner scanner = new Scanner(System.in);
public static void main(String[] args) {
System.out.println("This Evaluation is based on BODMAS rule\n");
evaluate();
}
private static void evaluate() {
StringBuilder finalStr = new StringBuilder();
System.out.println("Enter an expression to evaluate:");
String expr = scanner.nextLine();
if(isProperExpression(expr)) {
expr = replaceBefore(expr);
char[] temp = expr.toCharArray();
String operators = "(+-*/%)";
for(int i = 0; i < temp.length; i++) {
if((i == 0 && temp[i] != '*') || (i == temp.length-1 && temp[i] != '*' && temp[i] != '!')) {
finalStr.append(temp[i]);
} else if((i > 0 && i < temp.length -1) || (i==temp.length-1 && temp[i] == '!')) {
if(temp[i] == '!') {
StringBuilder str = new StringBuilder();
for(int k = i-1; k >= 0; k--) {
if(Character.isDigit(temp[k])) {
str.insert(0, temp[k] );
} else {
break;
}
}
Long prev = Long.valueOf(str.toString());
BigInteger val = new BigInteger("1");
for(Long j = prev; j > 1; j--) {
val = val.multiply(BigInteger.valueOf(j));
}
finalStr.setLength(finalStr.length() - str.length());
finalStr.append("(" + val + ")");
if(temp.length > i+1) {
char next = temp[i+1];
if(operators.indexOf(next) == -1) {
finalStr.append("*");
}
}
} else {
finalStr.append(temp[i]);
}
}
}
expr = finalStr.toString();
if(expr != null && !expr.isEmpty()) {
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
try {
System.out.println("Result: " + engine.eval(expr));
evaluate();
} catch (ScriptException e) {
System.out.println(e.getMessage());
}
} else {
System.out.println("Please give an expression");
evaluate();
}
} else {
System.out.println("Not a valid expression");
evaluate();
}
}
private static String replaceBefore(String expr) {
expr = expr.replace("(", "*(");
expr = expr.replace("+*", "+").replace("-*", "-").replace("**", "*").replace("/*", "/").replace("%*", "%");
return expr;
}
private static boolean isProperExpression(String expr) {
expr = expr.replaceAll("[^()]", "");
char[] arr = expr.toCharArray();
Stack<Character> stack = new Stack<Character>();
int i =0;
while(i < arr.length) {
try {
if(arr[i] == '(') {
stack.push(arr[i]);
} else {
stack.pop();
}
} catch (EmptyStackException e) {
stack.push(arr[i]);
}
i++;
}
return stack.isEmpty();
}
}
Please find the updated gist anytime here. Also comment if any issues are there. Thanks.
There are some perfectly capable answers here. However for non-trivial script it may be desirable to retain the code in a cache, or for debugging purposes, or even to have dynamically self-updating code.
To that end, sometimes it's simpler or more robust to interact with Java via command line. Create a temporary directory, output your script and any assets, create the jar. Finally import your new code.
It's a bit beyond the scope of normal eval() use in most languages, though you could certainly implement eval by returning the result from some function in your jar.
Still, thought I'd mention this method as it does fully encapsulate everything Java can do without 3rd party tools, in case of desperation. This method allows me to turn HTML templates into objects and save them, avoiding the need to parse a template at runtime.
import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;
class Calculate {
public static void main(String[] args) {
String strng = "8*-2*3*-1*10/2+6-2";
String[] oparator = {"+","-","*","/"};
List<String> op1 = new ArrayList<>();
String[] x = strng.split("");
int sayac=0;
for (String i : x) {
sayac ++;
for (String c : oparator) {
if (i.equals(c)) {
try {
int j = Integer.parseInt(strng.substring(0, sayac - 1));
op1.add(strng.substring(0, sayac - 1));
op1.add(c);
strng = strng.substring(sayac);
sayac = 0;
}catch (Exception e)
{
continue;
}
}
}
}
op1.add(strng);
ListIterator<String> it = op1.listIterator();
List<List> newlist = new ArrayList<>() ;
while (it.hasNext()) {
List<String> p= new ArrayList<>();
p.add(String.valueOf(it.nextIndex()));
p.add(it.next());
newlist.add(p);
}
int sayac2=0;
String oparatorvalue = "*";
calculate(sayac2,newlist,oparatorvalue);
String oparatorvalue2 = "/";
calculate(sayac2,newlist,oparatorvalue2);
String oparatorvalue3 = "+";
calculate(sayac2,newlist,oparatorvalue3);
String oparatorvalue4 = "-";
calculate(sayac2,newlist,oparatorvalue4);
System.out.println("Result:"+newlist.get(0).get(1));
}
private static void calculate(int sayac2, List<List> newlist, String oparatorvalue) {
while (sayac2<4){
try{
for (List j : newlist) {
if (j.get(1) == oparatorvalue) {
Integer opindex = newlist.indexOf(j);
Object sayi1 = newlist.get(opindex - 1).get(1);
Object sayi2 = newlist.get(opindex + 1).get(1);
int sonuc=0;
if (oparatorvalue.equals("*")){
sonuc = Integer.parseInt(sayi1.toString()) * Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("/")){
sonuc = Integer.parseInt(sayi1.toString()) / Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("+")){
sonuc = Integer.parseInt(sayi1.toString()) + Integer.parseInt(sayi2.toString());
}
if (oparatorvalue.equals("-")){
sonuc = Integer.parseInt(sayi1.toString()) - Integer.parseInt(sayi2.toString());
}
newlist.remove(opindex - 1);
newlist.remove(opindex - 1);
newlist.remove(opindex - 1);
List<String> sonuclist = new ArrayList<>();
sonuclist.add(String.valueOf(opindex - 1));
sonuclist.add(String.valueOf(sonuc));
newlist.add(opindex - 1, sonuclist);
}}}
catch (Exception e){
continue;
}
sayac2++;}
}
}
If you do not want to import heavy scripting library, you can use SimpleExpressionEvaluator directly into your code
Usage:
Expression.eval("1+2").asString(); // returns "3.0"
Expression.eval("1+2").asInt(); // returns 3
Expression.eval("2>3").asString(); // returns "false"
Expression.eval("2>3").asBoolean(); // returns false
Expression.eval("(3>2)||((2<4)&&(2>1))").asString(); // returns "true"
With variables:
HashMap<String, Object> st = new HashMap<String, Object>();
st.put("a",1);
st.put("b",2);
st.put("c",3);
st.put("d",4);
Expression.eval("a+b", st).asInt(); // or simply asString()
Expression.eval("a>b",st).asBoolean(); // or simply asString()
Expression.eval("(c>b)||((b<d)&&(b>a))",st).asBoolean(); // or simply asString()
Expression.eval("(c>2)||((2<d)&&(b>1))",st).asBoolean(); // or simply asString()
Using ExpressionBuilder:
Expression.expressionBuilder().putSymbol("a",2).putSymbol("b",3).build("(b>a)").evaluate()
The following resolved the issue:
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
String str = "4*5";
System.out.println(engine.eval(str));
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package sim;
import java.io.*;
import java.util.Arrays;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;
import static jdk.nashorn.internal.objects.NativeMath.max;
/**
*
* #author admin
*/
public class Sim {
public String[][] bigramizedWords = new String[500][100];
public String[] words = new String[500];
public File file1 = new File("file1.txt");
public File file2 = new File("file2.txt");
public int tracker = 0;
public double matches = 0;
public double denominator = 0; //This will hold the sum of the bigrams of the 2 words
public double res;
public double results;
public Scanner a;
public PrintWriter pw1;
public Sim(){
intialize();
// bigramize();
results = max(res);
System.out.println("\n\nThe Bigram Similarity value between " + words[0] + " and " + words[1] + " is " + res + ".");
pw1.close();
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
Sim si=new Sim();
// TODO code application logic here
}
public void intialize() {
int j[]=new int[35];
try {
File file1=new File("input.txt");
File file2=new File("out.txt");
Scanner a = new Scanner(file1);
PrintWriter pw1= new PrintWriter(file2);
int i=0,count = 0;
while (a.hasNext()) {
java.lang.String gram = a.next();
if(gram.startsWith("question")|| gram.endsWith("?"))
{
count=0;
count-=1;
}
if(gram.startsWith("[")||gram.startsWith("answer")||gram.endsWith(" ") )
{
//pw1.println(count);
j[i++]=count;
count=0;
//pw1.println(gram);
//System.out.println(count);
}
else
{
// System.out.println(count);
count+=1;
//System.out.println(count + " " + gram);
}
int line=gram.length();
int sa_length;
//int[] j = null;
int refans_length=j[1];
//System.out.println(refans_length);
for(int k=2;k<=35;k++)
// System.out.println(j[k]);
//System.out.println(refans_length);
for(int m=2;m<=33;m++)
{
sa_length=j[2];
//System.out.println(sa_length);
for(int s=0;s<=refans_length;s++)
{
for(int l=0;l<=sa_length;l++)
{
for (int x = 0; x <= line - 2; x++) {
int tracker = 0;
bigramizedWords[tracker][x] = gram.substring(x, x + 2);
System.out.println(gram.substring(x, x + 2) + "");
//bigramize();
}
// bigramize();
}
}
}
bigramize();
words[tracker] = gram;
tracker++;
}
//pw1.close();
}
catch (FileNotFoundException ex) {
Logger.getLogger(Sim.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void bigramize() {
//for(int p=0;p<=sa_length;p++)
denominator = (words[0].length() - 1) + (words[1].length() - 1);
for (int k = 0; k < bigramizedWords[0].length; k++) {
if (bigramizedWords[0][k] != null) {
for (int i = 0; i < bigramizedWords[1].length; i++) {
if (bigramizedWords[1][i] != null) {
if (bigramizedWords[0][k].equals(bigramizedWords[1][i])) {
matches++;
}
}
}
}
}
matches *= 2;
res = matches / denominator;
}
}
I have tried the above code for bigramizing the words in the file "input.txt" i have got the result of bigram but i didnt get the similarity value.
for e.g:
input file contains as
answer:
high
risk
simulate
behaviour
solution
set
rules
[2]
rules
outline
high
source
knowledge
[1]
set
rules
simulate
behaviour
in the above example I have to compare the words under answer with every word under [2] as {high,rules} {high,outline} {high,high} {high,source} {high,knowledge} and I have to store the maximum value of the above comparison and again the second word from answer is taken and then similar process is taken. At last, mean of maximum value of each iteration is taken.
The problem asks for an acm graphics program that reads a txt file like this:
R
FUN
SALES
RECEIPT
MERE#FARM
DOVE###RAIL
MORE#####DRAW
HARD###TIED
LION#SAND
EVENING
EVADE
ARE
D
and makes a crossword puzzle, with blank squares on letters, black squares on '#', and nothing on empty spaces. The problem also asks that "if the square is at the beginning of a word running across, down, or both, the square should contain a number that is assigned sequentially through the puzzle."
I have the square drawing working, but I'm stuck on drawing the numbers correctly. There is something wrong with how I'm detecting null space and black squares. Can someone tell me what I'm doing wrong, please?
Here is the code:
import acm.program.*;
import java.io.*;
import java.util.*;
import acm.graphics.*;
import java.awt.*;
public class Crossword extends GraphicsProgram {
public void run() {
String fileName = "crosswordfile.txt";
makeCrosswordPuzzle(fileName);
}
private static final int sqCon = 15; // constant for square x and y dimensions
private int y = 0;
public void makeCrosswordPuzzle(String fileName) {
BufferedReader rd;
int y = 0; // y value for the square being added during that loop. increments by sqCon after every line
int wordNumber = 1; // variable for numbers added to certain boxes. increments every time the program adds a number
try {
rd = new BufferedReader(new FileReader(fileName));
String line = rd.readLine(); //reads one line of the text document at a time and makes it a string
while (line != null) {
int x = 0;
for (int i = 0; i < line.length(); i++) {
char lineChar = line.charAt(i);// the character being examined for each loop
GRect whiteSq = new GRect(sqCon,sqCon); //GRect for blank squares
GRect blackSq = new GRect(sqCon,sqCon);//GRect for black squares
blackSq.setFilled(true);
blackSq.setFillColor(Color.BLACK);
if (lineChar == '#'){
add (blackSq,x,y);
}
if (Character.isLetter(lineChar)) {
add (whiteSq, x, y);
// if the element above or to the left of the current focus is null or blackSq, place the number and then increment wordNumber
GObject above = getElementAt(x+sqCon/2,y-sqCon/2);
GObject left = getElementAt(x-sqCon/2, y+sqCon/2);
GLabel wordNumberLabel = new GLabel(Integer.toString(wordNumber));
if (above == null || left == null || above == blackSq || left == blackSq) {
add(wordNumberLabel,x,y+sqCon);
wordNumber++;
}
}
x += sqCon;
}
line = rd.readLine();
y += sqCon;
}
rd.close();
}
catch (IOException e) {
throw new ErrorException(e);
}
}
}
Edited to add:
I copied your code over to my Eclipse and ran it. Here's the result.
You did fine on the upper half, but you missed the down numbers on the lower half.
Here's the same code, reformatted so it's easier to read.
import java.awt.Color;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import acm.graphics.GLabel;
import acm.graphics.GObject;
import acm.graphics.GRect;
import acm.program.GraphicsProgram;
import acm.util.ErrorException;
public class Crossword extends GraphicsProgram {
private static final long serialVersionUID = -7971434624427958742L;
public void run() {
// String fileName = "crosswordfile.txt";
String fileName = "C:/Eclipse/eclipse-4.2-work/com.ggl.testing/crosswordfile.txt";
makeCrosswordPuzzle(fileName);
}
private static final int sqCon = 15; // constant for square x and y
// dimensions
private int y = 0;
public void makeCrosswordPuzzle(String fileName) {
BufferedReader rd;
int y = 0; // y value for the square being added during that loop.
// increments by sqCon after every line
int wordNumber = 1; // variable for numbers added to certain boxes.
// increments every time the program adds a number
try {
rd = new BufferedReader(new FileReader(fileName));
String line = rd.readLine(); // reads one line of the text document
// at a time and makes it a string
while (line != null) {
int x = 0;
for (int i = 0; i < line.length(); i++) {
char lineChar = line.charAt(i);// the character being
// examined for each loop
GRect whiteSq = new GRect(sqCon, sqCon); // GRect for blank
// squares
GRect blackSq = new GRect(sqCon, sqCon);// GRect for black
// squares
blackSq.setFilled(true);
blackSq.setFillColor(Color.BLACK);
if (lineChar == '#') {
add(blackSq, x, y);
}
if (Character.isLetter(lineChar)) {
add(whiteSq, x, y);
// if the element above or to the left of the current
// focus is null or blackSq, place the number and then
// increment wordNumber
GObject above = getElementAt(x + sqCon / 2, y - sqCon
/ 2);
GObject left = getElementAt(x - sqCon / 2, y + sqCon
/ 2);
GLabel wordNumberLabel = new GLabel(
Integer.toString(wordNumber));
if (above == null || left == null || above == blackSq
|| left == blackSq) {
add(wordNumberLabel, x, y + sqCon);
wordNumber++;
}
}
x += sqCon;
}
line = rd.readLine();
y += sqCon;
}
rd.close();
} catch (IOException e) {
throw new ErrorException(e);
}
}
}
I followed the advice of my own comment. I created the crossword puzzle answer, numbered the crossword puzzle answer, and finally drew the crossword puzzle answer.
Here's the applet result:
I kept a List of crossword puzzle cells. That way, I could determine the length and the width of the puzzle by the number of characters on a row and the number of rows of the input text file. I didn't have to hard code the dimensions.
For each crossword cell, I kept track of whether or not it was a letter, and whether or not it was a dark space.
When determining where to put the numbers, I followed 2 rules.
An across number is placed where the cell left of the cell is empty or dark, and there are three or more letters across.
A down number is placed where the cell above the cell is empty or dark, there are three or more letters down, and there is no across number.
You can see in the code that I had to do some debug printing to get the crossword puzzle clue numbering correct. I broke the process into many methods to keep each method as simple as possible.
Finally, I drew the crossword puzzle answer from the information in the List.
Here's the code:
import java.awt.Color;
import java.awt.Point;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import acm.graphics.GLabel;
import acm.graphics.GRect;
import acm.program.GraphicsProgram;
import acm.util.ErrorException;
public class Crossword extends GraphicsProgram {
private static final boolean DEBUG = false;
private static final long serialVersionUID = -7971434624427958742L;
private List<CrosswordCell> crosswordCellList;
#Override
public void run() {
this.crosswordCellList = new ArrayList<CrosswordCell>();
// String fileName = "crosswordfile.txt";
String fileName = "C:/Eclipse/eclipse-4.2-work/" +
"com.ggl.testing/crosswordfile.txt";
try {
readCrosswordAnswer(fileName);
if (DEBUG) printCrosswordAnswer();
numberCrosswordCells();
if (DEBUG) printCrosswordAnswer();
drawCrosswordAnswer();
} catch (FileNotFoundException e) {
throw new ErrorException(e);
} catch (IOException e) {
throw new ErrorException(e);
}
}
private void readCrosswordAnswer(String fileName)
throws FileNotFoundException, IOException {
BufferedReader reader =
new BufferedReader(new FileReader(fileName));
String line = "";
int row = 0;
while ((line = reader.readLine()) != null) {
for (int column = 0; column < line.length(); column++) {
CrosswordCell cell = new CrosswordCell(column, row);
char lineChar = line.charAt(column);
if (lineChar == '#') {
cell.setDarkCell(true);
} else if (Character.isLetter(lineChar)) {
cell.setLetter(true);
}
crosswordCellList.add(cell);
}
row++;
}
reader.close();
}
public void printCrosswordAnswer() {
for (CrosswordCell cell : crosswordCellList) {
System.out.println(cell);
}
}
private void numberCrosswordCells() {
int clueNumber = 1;
for (CrosswordCell cell : crosswordCellList) {
if (cell.isLetter()) {
clueNumber = testCell(cell, clueNumber);
}
}
}
private int testCell(CrosswordCell cell, int clueNumber) {
Point p = cell.getLocation();
CrosswordCell leftCell = getLeftCell(p.x, p.y);
List<CrosswordCell> acrossList = getRightCells(p.x, p.y);
if (DEBUG) {
System.out.print(p);
System.out.println(", " + leftCell + " " +
acrossList.size());
}
if ((leftCell == null) && (acrossList.size() >= 3)) {
cell.setClueNumber(clueNumber++);
} else {
CrosswordCell aboveCell = getAboveCell(p.x, p.y);
List<CrosswordCell> downList = getBelowCells(p.x, p.y);
if (DEBUG) {
System.out.print(p);
System.out.println(", " + aboveCell + " " +
downList.size());
}
if ((aboveCell == null) && (downList.size() >= 3)) {
cell.setClueNumber(clueNumber++);
}
}
return clueNumber;
}
private CrosswordCell getAboveCell(int x, int y) {
int yy = y - 1;
return getCell(x, yy);
}
private CrosswordCell getLeftCell(int x, int y) {
int xx = x - 1;
return getCell(xx, y);
}
private List<CrosswordCell> getBelowCells(int x, int y) {
List<CrosswordCell> list = new ArrayList<CrosswordCell>();
for (int i = y; i < (y + 3); i++) {
CrosswordCell cell = getCell(x, i);
if (cell != null) {
list.add(cell);
}
}
return list;
}
private List<CrosswordCell> getRightCells(int x, int y) {
List<CrosswordCell> list = new ArrayList<CrosswordCell>();
for (int i = x; i < (x + 3); i++) {
CrosswordCell cell = getCell(i, y);
if (cell != null) {
list.add(cell);
}
}
return list;
}
private CrosswordCell getCell(int x, int y) {
for (CrosswordCell cell : crosswordCellList) {
Point p = cell.getLocation();
if ((p.x == x) && (p.y == y)) {
if (cell.isDarkCell()) {
return null;
} else if (cell.isLetter()){
return cell;
} else {
return null;
}
}
}
return null;
}
private void drawCrosswordAnswer() {
int sqCon = 32;
for (CrosswordCell cell : crosswordCellList) {
Point p = cell.getLocation();
if (cell.isDarkCell()) {
drawDarkCell(p, sqCon);
} else if (cell.isLetter()) {
drawLetterCell(cell, p, sqCon);
}
}
}
private void drawDarkCell(Point p, int sqCon) {
GRect blackSq = new GRect(sqCon, sqCon);
blackSq.setFilled(true);
blackSq.setFillColor(Color.BLACK);
add(blackSq, p.x * sqCon, p.y * sqCon);
}
private void drawLetterCell(CrosswordCell cell, Point p, int sqCon) {
GRect whiteSq = new GRect(sqCon, sqCon);
add(whiteSq, p.x * sqCon, p.y * sqCon);
if (cell.getClueNumber() > 0) {
String label = Integer.toString(cell.getClueNumber());
GLabel wordNumberLabel = new GLabel(label);
add(wordNumberLabel, p.x * sqCon + 2, p.y * sqCon + 14);
}
}
class CrosswordCell {
private boolean darkCell;
private boolean isLetter;
private int clueNumber;
private Point location;
public CrosswordCell(int x, int y) {
this.location = new Point(x, y);
this.clueNumber = 0;
this.darkCell = false;
this.isLetter = false;
}
public boolean isDarkCell() {
return darkCell;
}
public void setDarkCell(boolean darkCell) {
this.darkCell = darkCell;
}
public boolean isLetter() {
return isLetter;
}
public void setLetter(boolean isLetter) {
this.isLetter = isLetter;
}
public int getClueNumber() {
return clueNumber;
}
public void setClueNumber(int clueNumber) {
this.clueNumber = clueNumber;
}
public Point getLocation() {
return location;
}
#Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("CrosswordCell [location=");
builder.append(location);
builder.append(", clueNumber=");
builder.append(clueNumber);
builder.append(", darkCell=");
builder.append(darkCell);
builder.append(", isLetter=");
builder.append(isLetter);
builder.append("]");
return builder.toString();
}
}
}
Alright so here is my problem and my question to you.....
I have a game in which it needs to load images from the jar file (all the images are packed into the jar file like so):
I first have the unzip of the jar file:
Then it goes to:
Then inside each of those folder i have something that looks like this:
Now reminder above is the Jarfile GameClient.jar unziped and you see where the cards are in it.
So here is my code for trying to load each and every one of those images into memory
private void addCardsAndChangeSize() throws IOException
{
String tempString;
ImageIcon tempIcon;
allCards.clear();
ClassLoader cldr = this.getClass().getClassLoader();
URL imageURL;
for(int i = 0; i < all.length; i++)
{
for(int x = 0; x < clubs.length; x++)
{
tempString = all[i][x];
tempString = "/cards/"+cardFolders[i]+"/"+tempString;
imageURL = cldr.getResource(tempString);
tempIcon = resizeImage(new ImageIcon(imageURL),70,70,false);
tempString = all[i][x];
tempIcon.setDescription(tempString);
allCards.add(tempIcon);
}
}
backCard = resizeImage(new ImageIcon(cldr.getResource(back)),70,70,false);
}
So i call that in the contructor to load all the images into an ArrayList here is the whole class if you want to know what i do.
package global;
import java.awt.*;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.swing.*;
public class Cards
{
private ImageIcon backCard = new ImageIcon("cards/backCard.jpg");
private String back = "/cards/backCard.jpg";
private String[] cardFolders = {
"clubs","diamonds","hearts","spades"
};
private String[] clubs = {
"aceClubs.jpg","eightClubs.jpg","fiveClubs.jpg","fourClubs.jpg","jackClubs.jpg",
"kingClubs.jpg","nineClubs.jpg","queenClubs.jpg","sevenClubs.jpg","sixClubs.jpg",
"tenClubs.jpg","threeClubs.jpg","twoClubs.jpg"
};
private String[] diamonds = {
"aceDia.jpg","eightDia.jpg","fiveDia.jpg","fourDia.jpg","jackDia.jpg","kingDia.jpg",
"nineDia.jpg","queenDia.jpg","sevenDia.jpg","sixDia.jpg","tenDia.jpg","threeDia.jpg",
"twoDia.jpg"
};
private String[] hearts = {
"aceHearts.jpg","eightHearts.jpg","fiveHearts.jpg","fourHearts.jpg","jackHearts.jpg",
"kingHearts.jpg","nineHearts.jpg","queenHearts.jpg","sevenHearts.jpg","sixHearts.jpg",
"tenHearts.jpg","threeHearts.jpg","twoHearts.jpg"
};
private String[] spades = {
"aceSpades.jpg","eightSpades.jpg","fiveSpades.jpg","fourSpades.jpg","jackSpades.jpg",
"kingSpades.jpg","nineSpades.jpg","queenSpades.jpg","sevenSpades.jpg","sixSpades.jpg",
"tenSpades.jpg","threeSpades.jpg","twoSpades.jpg"
};
private String[][] all = {
clubs,diamonds,hearts,spades
};
private ArrayList<ImageIcon> allCards = new ArrayList<ImageIcon>();
public Cards()
{
try
{
addCardsAndChangeSize();
shuffle();
}
catch(Exception e)
{e.printStackTrace();}
}
/**
* #param x Cards name with extension
* #return Face Value of Card
*/
public static int getFaceValue(String x)
{
int face = 0;
switch(x)
{
case "aceClubs.jpg":
case "aceDia.jpg":
case "aceHearts.jpg":
case "aceSpades.jpg":
face = 1;
break;
case "eightClubs.jpg":
case "eightDia.jpg":
case "eightHearts.jpg":
case "eightSpades.jpg":
face = 8;
break;
case "fiveClubs.jpg":
case "fiveDia.jpg":
case "fiveHearts.jpg":
case "fiveSpades.jpg":
face = 5;
break;
case "fourClubs.jpg":
case "fourDia.jpg":
case "fourHearts.jpg":
case "fourSpades.jpg":
face = 4;
break;
case "jackClubs.jpg":
case "jackDia.jpg":
case "jackHearts.jpg":
case "jackSpades.jpg":
case "kingClubs.jpg":
case "kingDia.jpg":
case "kingHearts.jpg":
case "kingSpades.jpg":
case "queenClubs.jpg":
case "queenDia.jpg":
case "queenHearts.jpg":
case "queenSpades.jpg":
case "tenClubs.jpg":
case "tenDia.jpg":
case "tenHearts.jpg":
case "tenSpades.jpg":
face = 10;
break;
case "twoClubs.jpg":
case "twoDia.jpg":
case "twoHearts.jpg":
case "twoSpades.jpg":
face = 2;
break;
case "threeClubs.jpg":
case "threeDia.jpg":
case "threeHearts.jpg":
case "threeSpades.jpg":
face = 3;
break;
case "sixClubs.jpg":
case "sixDia.jpg":
case "sixHearts.jpg":
case "sixSpades.jpg":
face = 6;
break;
case "sevenClubs.jpg":
case "sevenDia.jpg":
case "sevenHearts.jpg":
case "sevenSpades.jpg":
face = 7;
break;
case "nineClubs.jpg":
case "nineDia.jpg":
case "nineHearts.jpg":
case "nineSpades.jpg":
face = 9;
break;
}
return face;
}
//shuffles all the cards in the deck
private void shuffle()
{
long seed = System.nanoTime();
Collections.shuffle(allCards, new Random(seed));
}
/**
* Chooses a card at random from the deck. Also removes that card when chosen
* #return randomly chosen card
*/
public ImageIcon getRandomCard()
{
int index = ((int)Math.random() * allCards.size());
return allCards.remove(index);
}
/**
* #return Image of the back of a card
*/
public ImageIcon getBackCard()
{return backCard;}
public static ImageIcon parseImage(String x)
{
if(x.contains("Dia"))
return new ImageIcon("cards/diamonds/"+x);
else
if(x.contains("Clubs"))
return new ImageIcon("cards/clubs/"+x);
else
if(x.contains("Hearts"))
return new ImageIcon("cards/hearts/"+x);
else
if(x.contains("Spades"))
return new ImageIcon("cards/spades/"+x);
return null;
}
//adds all the cards and adds a description to them loaded into memory
private void addCardsAndChangeSize() throws IOException
{
String tempString;
ImageIcon tempIcon;
allCards.clear();
ClassLoader cldr = this.getClass().getClassLoader();
URL imageURL;
for(int i = 0; i < all.length; i++)
{
for(int x = 0; x < clubs.length; x++)
{
tempString = all[i][x];
tempString = "/cards/"+cardFolders[i]+"/"+tempString;
imageURL = cldr.getResource(tempString);
tempIcon = resizeImage(new ImageIcon(imageURL),70,70,false);
tempString = all[i][x];
tempIcon.setDescription(tempString);
allCards.add(tempIcon);
}
}
backCard = resizeImage(new ImageIcon(cldr.getResource(back)),70,70,false);
}
//resizes images
public ImageIcon resizeImage(ImageIcon imageIcon, int width, int height, boolean max)
{
Image image = imageIcon.getImage();
Image newimg = image.getScaledInstance(-1, height, java.awt.Image.SCALE_SMOOTH);
int width1 = newimg.getWidth(null);
if ((max && width1 > width) || (!max && width1 < width))
newimg = image.getScaledInstance(width, -1, java.awt.Image.SCALE_SMOOTH);
return new ImageIcon(newimg);
}
}
I keep getting null pointer exception on the tempIcon = resizeImage(new ImageIcon(imageURL),70,70,false);
Can anyone tell me why this isn't loading the images properly? Reminder i am pre-loading them into memory. My question is not how to make this better i am just simply asking what am i doing wrong with the class loader and stuff like that......
I am somewhat new at java and i know some of this code will look horrible to you but please again i am not asking how to make this code "pro" im just looking for the explanation why its giving me null.
Thanks!
P.S. If you need more pictures of info or w.e. i will try to put that up right away
Your problem is that cldr.getResource(tempString); does not return object but null. Then, something is wrong with tempString. Classloader cannot find this file, so returns null.
Change tempString = "/cards/"+cardFolders[i]+"/"+tempString;
To tempString = "cards/"+cardFolders[i]+"/"+tempString;
You should be using the getResource of Class, not ClassLoader. The getResource method in Class does useful transformations on the path before giving it to the ClassLoader version of the method, like deciding if the path is relative to the class or absolute, and so ClassLoader doesn't expect to see things like / at the start of the path. You can see this clearly in the getResource javadoc.
So i found out the solution i still don't quite understand why this is the answer but here ya go.
This is the revised code and works fine
private void addCardsAndChangeSize() throws Exception
{
String tempString;
ImageIcon tempIcon;
allCards.clear();
URL imageURL;
for(int i = 0; i < all.length; i++)
{
for(int x = 0; x < clubs.length; x++)
{
tempString = all[i][x];
tempString = "/cards/"+cardFolders[i]+"/"+tempString;
imageURL = this.getClass().getResource(tempString);
System.out.println(tempString);
System.out.println(imageURL == null);
tempIcon = resizeImage(new ImageIcon(imageURL),70,70,false);
tempString = all[i][x];
tempIcon.setDescription(tempString);
allCards.add(tempIcon);
}
}
backCard = resizeImage(new ImageIcon(this.getClass().getResource(back)),70,70,false);
}
You have to have that "/cards/" and also you this.getClass().getResource(String res);
Thanks for all your help guys!