using reflection method to call function in Selenium - java

given a TestNG test within Selenium
public boolean TestTabTagLog( Matters m, String logfile) {
boolean passFail = false;
if( m == null) {
System.out.println("TestTagTabLog: m is null and should not be!");
} else {
System.out.println("TestTabTagLog: m.getPageName: " + m.getPageName());
/* m does get here and is populated , great*/
}
WebElement divTopTabs = m.getDriver().findElement(By.id("tab-topTabs"));
// --- this fails with an NoSuchElementException --- why? -- and more importantly, how to fix?
/* more logic goes here */
return passFail;
}
#Test()
public boolean runTest( Matters m, String testToRun) {
boolean passFail = false;
List<Boolean> results = new LinkedList<Boolean>();
Matters m = new Matters();
WebElement divTopTabs = m.getDriver().findElement(By.id("tab-topTabs"));
// m and divTopTabs exist and are populated
List<String> list_tabName = new LinkedList<String>();
list_tabName.add("TagLog");
for( String tabName : list_tabName) {
String functName = "TestTab" + tabName;
try {
Class c = Class.forName("foo.fighters.Test");
Object obj = c.newInstance();
Class[] params = new Class[2];
params[0] = Matters.class;
params[1] = String.class;
Method mth = c.getDeclaredMethod( functName, params);
mth.setAccessible(true);
Boolean result = (Boolean) mth.invoke( obj, m, "C:/User/Me/alogfile.txt");
results.add( result);
} catch ( ClassNotFoundException cnfe) {
System.out.println("cnfe:" + cnfe.getMessage());
} catch ( InstantiantionException | IllegalAccessException iae) {
System.out.println("iae:" + iae.getMessage());
} catch ( NoSuchMethodException | SecurityException nsme) {
System.out.println("nsme:" + nsme.getMessage());
} catch ( IllegalArgumentException | InvocationTargetException ite ) {
System.out.println("ite:" + ite.getMessage());
}
}
Boolean atLeastOneTestFailed = results.stream()filter(e -> e == false).findAny().isPresent();
if( !atLeastOneTestFailed) {
passFail = true;
}
return passFail;
}
I'm trying to dynamically call my functions by name - hoping to prevent coding a giant switch/case statement.
Within the top function runTest() I can find m and use m to find divTopTabs.
I can pass m to called function TestTabTagLog but within TestTabTagLog canNOT use m to find divTopTags. That's my problem.
I have tried passing in divTopTabs to TestTabTagLog as an argument but that doesn't work for some reason, maybe cuz it's a WebElement and that is a class inside openqa ie not a class I create within my project like Matters. But it that's true why can I pass in the String logfile ?
A little out of my depth here, could use some help/advice/constructive critism
TIA,
Still-learning Steve

Related

How to instantiate objects and passing it to other constructors in a loop

That's a question about logic, to be honest, but i can't think in a answer to it. Basically, i have this code that loads decorators and store the Class in decoratorConstructors:
Collection<String> decorators = (Collection<String>) (((javax.swing.JButton)e.getSource()).getClientProperty( "selectedDecoratorsNames"));
ArrayList<Constructor> decoratorConstructors = new ArrayList();
String interfaceClassName = "interfaces.PizzaComponent";
Class interfaceClass = null;
Method interfaceMethodPrepare = null;
for(String decorator: decorators) {
Constructor decoratorConstructor;
Class metaFactory = null;
String decoratorName = decoratorNames.get(decorator);
String className = decoratorName + "." + decorator;
interfaceClass = Class.forName(interfaceClassName, true, sysLoader);
metaFactory = Class.forName(className, true, sysLoader);
interfaceMethodPrepare = interfaceClass.getDeclaredMethod("preparar");
decoratorConstructors.add(metaFactory.getConstructor(interfaceClass));
}
Object interfaceObject = interfaceClass;
System.out.println(decoratorConstructors);
Object pizza = interfaceClass.cast(decoratorConstructors.get(2).newInstance(
decoratorConstructors.get(1).newInstance(
decoratorConstructors.get(0).newInstance(
new PizzaSimples()
)
)
));
interfaceMethodPrepare.invoke(pizza);
How could i run this piece of code on a loop:
Object pizza = interfaceClass.cast(decoratorConstructors.get(2).newInstance(
decoratorConstructors.get(1).newInstance(
decoratorConstructors.get(0).newInstance(
new PizzaSimples()
)
)
));
Well, i've managed to do what i was trying to do. I used a recursive function:
Object pizza = instantiate(decoratorConstructors, interfaceClass, decoratorConstructors.size() - 1, pizzaSimplesConstructor);
private Object instantiate(ArrayList<Constructor> decoratorConstructors, Class interfaceClass, int i, Constructor pizzaSimplesConstructor) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Object pizza = null;
if(i > -1) {
System.out.println("\nInstanciando " + decoratorConstructors.get(i));
pizza = decoratorConstructors.get(i).newInstance(instantiate(decoratorConstructors, interfaceClass, --i, pizzaSimplesConstructor));
return pizza;
}else {
return pizzaSimplesConstructor.newInstance();
}
}

How to convert string in a txt document to code? [duplicate]

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));

Pass parameter value from my implementation service to my RestController java springboot

I'm having a trouble passing the value of error i get when im returning the results of a table.
I have a method in my ServiceImpl class which return results for the table and also counts the amount of errors.
public List<Flow> getAllProcessContextWithCriteriaAndFlowCode(
String startDate, String endDate, String flowCode) {
List<FlowDto> flowDtos = new ArrayList<>(500);
flowDtos = processContextRepository
.fetch(startDate,
endDate, flowCode);
List<Flow> flows = new ArrayList();
// bodyguard
if (flowDtos == null || flowDtos.size() == 0) {
return flows;
}
int counter = 0;
StringBuilder idFonctionnelBuilder = new StringBuilder();
FlowDto currentFlowDto = null;
FlowState flowState = new FlowState();
FlowDto nextFlowDto = null;
Flow flowTemp = null;
Map<String, String> mapFlowIdsAndIdF = new HashMap<>();
int iNbreError = 0;
String sTempError = "";
for (int i = 0; i < flowDtos.size(); i++) {
currentFlowDto = flowDtos.get(i);
if ((i + 1) < flowDtos.size()) {
nextFlowDto = flowDtos.get(i + 1);
if (((nextFlowDto.getFlowId()
.equals(currentFlowDto.getFlowId())))) {
idFonctionnelBuilder.append(currentFlowDto.getIdf() + ", ");
continue;
} else {
flowTemp = new Flow();
flowTemp.setFlowId(currentFlowDto.getFlowId());
flowTemp.setLogRole(currentFlowDto.getLogRole());
Date date = null;
try {
date = inputFormat.parse(currentFlowDto
.getContextTime());
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
flowTemp.setContextTime(outputFormat.format(date));
if (currentFlowDto.getLogRole() != null) {
iNbreError++;
flowTemp.setNbreError(iNbreError);
} else {
flowTemp.setNbreError(iNbreError);
}
flowTemp.setNbreError(iNbreError);
flows.add(flowTemp);
}
} else {
flowTemp = new Flow();
if (currentFlowDto.getLogRole() != null) {
iNbreError++;
flowTemp.setNbreError(iNbreError);
} else {
flowTemp.setNbreError(iNbreError);
}
flowTemp.setContextTime(outputFormat.format(date));
flows.add(flowTemp);
}
}
LOGGER.info("[ getAllProcessContextWithCriteriaAndFlowCode ] iNbreError : "
+ iNbreError);
getNbreError(iNbreError);
return flows;
}
Then i have another method in the same class ServiceImpl who get the number of errors and set it in a variable, the result print is always the right one here.
public int getNbreError( int iNbreError){
System.out.println("HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH");
System.out.println(iNbreError);
setCountError(iNbreError);
System.out.println("HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH");
System.out.println(countError);
return countError;
}
What i want to do is send this value(counterror) to my RestController which is in another class called RestController so i can send it to my angular front
#GetMapping(value = "/nbreError")
public int getCountError() {
FMServiceImpl flows = new FMServiceImpl();
int countError = 0;
int iNbreError = 0;
return fmService.getNbreError( iNbreError);
}
}
Actually the result is always 0.
Thanks for your any help or advice :)
Don't use getMethod to modify data, check principle Command–query separation (CQS)
Don't create FMServiceImpl manually, Inject FMServiceImpl as dependence to your controller. in spring, Service keeps the state by default.

List<> - Reflection

I'm trying to determine if a list contains a object, if it does then run a method to clear the original list (in a singleton class), then repopulate the list minus the one I ran the condition over.
public void removeSelectedItem(Object obj){
SearchBuilder builder = SearchBuilder.getInstance();
try {
String methodName = labelToMethod.get(getTitle());
if( methodName == null ){
methodName = getTitle().replace(" ","");
}
Method m = builder.getClass().getMethod("get"+methodName);
Object r = m.invoke(builder);
if( r != null ){
if( r instanceof Integer ){
if( ((Integer) r).intValue() == ((Integer) obj).intValue() ) {
setSelectedItem(null);
}
} else if ( r instanceof String ){
if(r.equals(obj)) {
setSelectedItem(null);
}
} else if ( r instanceof ArrayList ){
Log.d("TEST",((ArrayList) r).size()+"");
if( ((ArrayList) r).contains(obj) ){
Log.d("TEST", "R CONTAINS OBJ");
Log.d("TEST", "BEFORE: " + ((ArrayList) r).size() + "");
clearSelectedItem();
Log.d("TEST","AFTER: " + ((ArrayList) r).size() + "");
for ( int i = 0; i < ((ArrayList) r).size(); i++ ){
Log.d("TEST","IN FOR LOOP" + i);
if( !((ArrayList) r).get(i).equals(obj) ){
Log.d("TEST", "SETTING VALUES");
setSelectedItem(((ArrayList) r).get(i));
}
}
}
}
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
The clearSelectedItem method is:
public void clearSelectedItem(){
SearchBuilder builder = SearchBuilder.getInstance();
try {
String methodName = labelToMethod.get(getTitle());
if( methodName == null ){
methodName = getTitle().replace(" ","");
}
Method m = builder.getClass().getMethod("clear"+methodName);
m.invoke(builder);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
The output I'm getting is:
D/TEST : 2
D/TEST : R CONTAINS OBJ
D/TEST : BEFORE: 2
D/TEST : AFTER: 0
So it's not entering the loop, as the ArrayList size has been reduced to 0. But what I don't understand is, why has the ArrayList been reduced? Surely the object has been set as part of the m.invoke call earlier in the removeSelectedItem method, and the clearSelectedItem doesn't touch this response?
I'm rather new to Java, so any insight would be great!
EDIT:
So I've managed to solve my problem, but would still really like some insight into what's going on...
I've solved it by cloning the ArrayList:
} else if ( r instanceof ArrayList ){
Object c = ((ArrayList) r).clone();
if( ((ArrayList) c).contains(obj) ){
clearSelectedItem();
for ( int i = 0; i < ((ArrayList) c).size(); i++ ){
if( !((ArrayList) c).get(i).equals(obj) ){
setSelectedItem(((ArrayList) c).get(i));
}
}
}
}
So I dont understand why you are repopulating the list itself,
would it be much cleaner or neat if you just use
if(list.contain(object))
{
list.remove(object);
}
or if you want to remove all of them just use
while(list.contain(object))
{
list.remove(object);
}
So after a little more research, Java is pass-by-value, which means that it passes the reference to the ArrayList, rather than create a new ArrayList with the same values. Amending Object r in any way affects the original ArrayList in SearchBuilder itself.
http://www.javaranch.com/campfire/StoryPassBy.jsp

Are there equivalents to Python's eval() and exec() in Java? [duplicate]

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));

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