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String Index Exception

I was trying to convert an expression from infix form to postfix form.I used String a, p , s for stack, postfix result expression, input expression respectively.
Every time I am getting this error:
Exception in thread "main" java.lang.StringIndexOutOfBoundsException:
String index out of range: -1 at
java.lang.String.charAt(String.java:658) at
javaapplication4.A.conversion(A.java:50) at
javaapplication4.A.main(A.java:83)
Please help me how can I solve it.
Here is my code:
import java.util.Scanner;
public class A {
String a="(", s = "", p = "";
int i, n = 1, top = 0, pp = 0;
void push(char ch) {
a = a + ch;
top = n;
n++;
}
void pop() {
n--;
top--;
}
int prio(char ch) {
int f = -1;
if (ch == '(') {
f = 0;
} else if (ch == '+' || ch == '-') {
f = 1;
} else if (ch == '*' || ch == '/' || ch == '%') {
f = 2;
} else if (ch == '^') {
f = 3;
}
return f;
}
void conversion() {
System.out.print("Enter infix form: ");
Scanner sd = new Scanner(System.in);
s = sd.nextLine();
//System.out.println(s);
int t, j, sz;
sz = s.length();
for (i = 0; i < sz; i++) {
if (s.charAt(i) >= '0' && s.charAt(i) <= '9') {
p = p + s.charAt(i);
pp++;
} else if (s.charAt(i) == '(') {
push('(');
} else if (s.charAt(i) == '-' || s.charAt(i) == '+' || s.charAt(i) == '*' || s.charAt(i) == '/' || s.charAt(i) == '%' || s.charAt(i) == '^') {
j = prio(s.charAt(i));
t = prio(a.charAt(top));
//System.out.println(t+" "+j);
while (j <= t) {
p = p + a.charAt(top);
pp++;
pop();
t = prio(a.charAt(top));
}
push(s.charAt(i));
} else if (s.charAt(i) == ')') {
while (a.charAt(top) != '(') {
p = p + a.charAt(top);
pp++;
pop();
}
pop();
}
}
while (a.charAt(top) != '(') {
p = p + a.charAt(top);
pp++;
pop();
}
pop();
}
void postfix() {
System.out.print("postfix form is: ");
System.out.println(p);
}
public static void main(String args[]) {
A h = new A();
h.conversion();
h.postfix();
//System.out.println(h.a);
//System.out.println(h.s);
}
}

Can you confirm if the error is here?
while (a.charAt(top) != '(')
Inside the loop you continuously pop(), which decrements from top, which has the risk of going negative if a match is never found. Even if the error is not here, it should check for that condition.

You may have made an extra pop() definition. Can you check this?

how to check number exists between braces

import java.util.Stack;
import java.util.Scanner;
public class CheckValidLocationofParenthensies {
public static void main(String args[]) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter five data");
String input1 = scanner.next();
balancedParenthensies(input1);
}
public static boolean balancedParenthensies(String s) {
Stack<Character> stack = new Stack<Character>();
for(int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if(c == '[' || c == '(' || c == '{' ) {
stack.push(c);
if(c == '[') {
newvalueforforward(s,']', i);
}
if(c == '{') {
newvalueforforward(s,'}', i);
}
if(c == '(') {
newvalueforforward(s,')', i);
}
} else if(c == ']') {
if(stack.isEmpty() || stack.pop() != '[') {
newvalue(s,'[', i);
return false;
}
} else if(c == ')') {
if(stack.isEmpty() || stack.pop() != '(') {
newvalue(s,'(', i);
return false;
}
} else if(c == '}') {
if(stack.isEmpty() || stack.pop() != '{') {
newvalue(s,'{', i);
return false;
}
}
}
return stack.isEmpty();
}
public static void newvalueforforward(String userval,char value,int decremntval) {
for(int i = 0; i < userval.length(); i++){
StringBuilder newvalue = new StringBuilder(userval);
int location=i;
newvalue.insert(i, value);
boolean valid= checkingnewvalueisValidorNot(newvalue, location);
location=i+1;
if(valid) {
System.out.println(newvalue+" "+""+location);
}
}
}
public static void newvalue(String userval,char value,int decremntval) {
for(int i = decremntval; i >= 0; i--){
StringBuilder newvalue = new StringBuilder(userval);
int location=decremntval - i;
newvalue.insert(decremntval - i, value);
boolean valid= checkingnewvalueisValidorNot(newvalue, location);
if(valid) {
System.out.println(newvalue+" "+""+location);
}
}
}
public static boolean checkingnewvalueisValidorNot(StringBuilder userval,int validpath) {
Stack<Character> stack = new Stack<Character>();
for(int i = 0; i < userval.length(); i++) {
char c = userval.charAt(i);
if(c == '[' || c == '(' || c == '{' ) {
stack.push(c);
} else if(c == ']') {
if(stack.isEmpty() || stack.pop() != '[') {
return false;
}
} else if(c == ')') {
if(stack.isEmpty() || stack.pop() != '(') {
return false;
}
} else if(c == '}') {
if(stack.isEmpty() || stack.pop() != '{') {
return false;
}
}
}
return stack.isEmpty();
}
}
Above is the code i have written to check whether input string contains all balanced brackets if it is not balanced then get missing bracket and place bracket in all index then again check whether string is balanced or not.
I got valid output but problem is between i bracket there should be a intergers
here is input and outputs
input missing outputs
{[(2+3)*6/10} ] {[](2+3)*6/10} 3 not valid(no numbres btn bracket)
{[(2+3)]*6/10} 8 valid
{[(2+3)*]6/10} 9 not valid(after * no number)
{[(2+3)*6]/10} 10 valid
{[(2+3)*6/]10} 11 not valid( / before bracket)
{[(2+3)*6/1]0} 12 not valid( / btn num bracket)
{[(2+3)*6/10]} 13 valid
i am failing to do proper validation to my output.

Before the bracket there may be:
number
closing bracket
After the bracket there may be:
operator
closing bracket
end of expression
(ignoring any whitespace)

Balance Check in Java

This is code for checking balance symbol.
However, when I try to fit in a Tester,
It does not show the anwer correctly.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class BalanceCheck {
private static Scanner in;
public static void main(String[] args){
if(args.length > 0){
System.out.println(args[0]);
try {
in = new Scanner(new File(args[0]));
MyStack<Character> stack = new MyStack<>();
String str;
char ch;
while(in.hasNext()){
str = in.next();
for(int i = 0; i < str.length(); ++i){
ch = str.charAt(i);
if(ch == '(' || ch == '[' || ch == '{' ||
(ch == '/' && i < str.length() - 1 && str.charAt(i+1) == '*')){
stack.push(ch);
}
else if(ch == ')'){
if(stack.isEmpty() || stack.pop() != ch){
System.out.println(") is mismatched");
return;
}
}
else if(ch == ']'){
if(stack.isEmpty() || stack.pop() != ch){
System.out.println("] is mismatched");
return;
}
}
else if(ch == '}'){
if(stack.isEmpty() || stack.pop() != ch){
System.out.println("} is mismatched");
return;
}
}
else if(ch == '*' && i < str.length() - 1 && str.charAt(i+1) == '/'){
if(stack.isEmpty() || stack.pop() != '/'){
System.out.println("*/ is mismatched");
return;
}
}
else if(ch == '"'){
if(stack.isEmpty() || stack.top() == '"'){
if(!stack.isEmpty())
stack.pop();
}
else{
stack.push(ch);
}
}
}
}
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
else{
System.out.println("Command line argument is not provided..");
}
}
}
For instance, if I compile this tester,
/*this tests an unbalanced [ operator*/
public class Test1 {
/* this is the main method */
public static void main(String[ ) args) {
String ghana = "hello";
int test = testing();
}
public int testing() {
/*checking this too */
/* and this */
return 1;
}
}
It should show [ is mismatched. But, it shows /* is mismatched.
Please let me know solution.
And I have to create a Tester file for this code above.
How can I code a tester for this?
Thanks,

Think about what happens with the very first line:
/*this tests an unbalanced [ operator*/
When you hit the '*/', there is a '[' on the top of the stack.
You need to track when you are inside a comment so that you can ignore everything until the end.
Whenever you have an issue like this, you need to use a debugger.

Custom Tokenizer, Iterator with quotes

Maybe some one can help?
How to modify this method next() that the next token can be: 'abc' text with the quotes.
Now if the text contains quote are throwed ExpressionException Unknown operator ''' at position...
#Override
public String next() {
StringBuilder token = new StringBuilder();
if (pos >= input.length()) {
return previousToken = null;
}
char ch = input.charAt(pos);
while (Character.isWhitespace(ch) && pos < input.length()) {
ch = input.charAt(++pos);
}
if (Character.isDigit(ch)) {
while ((Character.isDigit(ch) || ch == decimalSeparator)
&& (pos < input.length())) {
token.append(input.charAt(pos++));
ch = pos == input.length() ? 0 : input.charAt(pos);
}
} else if (ch == minusSign
&& Character.isDigit(peekNextChar())
&& ("(".equals(previousToken) || ",".equals(previousToken)
|| previousToken == null || operators
.containsKey(previousToken))) {
token.append(minusSign);
pos++;
token.append(next());
} else if (Character.isLetter(ch)) {
while ((Character.isLetter(ch) || Character.isDigit(ch) || (ch == '_')) && (pos < input.length())) {
token.append(input.charAt(pos++));
ch = pos == input.length() ? 0 : input.charAt(pos);
}
} else if (ch == '(' || ch == ')' || ch == ',') {
token.append(ch);
pos++;
//FIXME
else if (ch == '\''){
pos++;
String temp = "\'"+next()+"\'";
token.append(temp);
pos++;
}
//
} else {
while (!Character.isLetter(ch) && !Character.isDigit(ch)
&& !Character.isWhitespace(ch) && ch != '('
&& ch != ')' && ch != ',' && (pos < input.length())) {
token.append(input.charAt(pos));
pos++;
ch = pos == input.length() ? 0 : input.charAt(pos);
if (ch == minusSign) {
break;
}
}
if (!operators.containsKey(token.toString())) {
throw new ExpressionException("Unknown operator '" + token
+ "' at position " + (pos - token.length() + 1));
}
}
return previousToken = token.toString();
}
eval
public Object eval() {
Stack<Object> stack = new Stack<Object>();
for (String token : getRPN()) {
mylog.pl("Reverse polish notation TOKEN : " + token + " RPN size: " + getRPN().size() );
if (operators.containsKey(token)) {
Object v1 = stack.pop();
Object v2 = stack.pop();
stack.push(operators.get(token).eval(v2, v1));
} else if (variables.containsKey(token)) {
stack.push(variables.get(token).round(mc));
} else if (functions.containsKey(token.toUpperCase())) {
Function f = functions.get(token.toUpperCase());
ArrayList<Object> p = new ArrayList<Object>(f.getNumParams());
for (int i = 0; i < f.numParams; i++) {
p.add(0, stack.pop());
}
Object fResult = f.eval(p);
stack.push(fResult);
} else if (isDate(token)) {
Long date = null;
try {
date = SU.sdf.parse(token).getTime();
} catch (ParseException e) {/* IGNORE! */
}
stack.push(new BigDecimal(date, mc));
} else {
if (BusinessStrategy.PREFIX_X.equals(Character.toString(token.charAt(0)))) {
stack.push(token);
} else {
stack.push(new BigDecimal(token, mc));
}
}
}
return stack.pop();
}
Reverse notation
private List<String> getRPN() {
if (rpn == null) {
rpn = shuntingYard(this.expression);
}
return rpn;
}
Yard
private List<String> shuntingYard(String expression) {
List<String> outputQueue = new ArrayList<String>();
Stack<String> stack = new Stack<String>();
Tokenizer tokenizer = new Tokenizer(expression);
String lastFunction = null;
while (tokenizer.hasNext()) {
String token = tokenizer.next();
if (isNumber(token)) {
outputQueue.add(token);
} else if (variables.containsKey(token)) {
outputQueue.add(token);
} else if (functions.containsKey(token.toUpperCase())) {
stack.push(token);
lastFunction = token;
} else if (Character.isLetter(token.charAt(0))) {
if ("\'".equals(Character.toString(token.charAt(0)))){
outputQueue.add(token);
} else {
stack.push(token);
}
} else if (",".equals(token)) {
while (!stack.isEmpty() && !"(".equals(stack.peek())) {
outputQueue.add(stack.pop());
}
if (stack.isEmpty()) {
throw new ExpressionException("Parse error for function '"
+ lastFunction + "'");
}
} else if (operators.containsKey(token)) {
Operator o1 = operators.get(token);
String token2 = stack.isEmpty() ? null : stack.peek();
while (operators.containsKey(token2)
&& ((o1.isLeftAssoc() && o1.getPrecedence() <= operators
.get(token2).getPrecedence()) || (o1
.getPrecedence() < operators.get(token2)
.getPrecedence()))) {
outputQueue.add(stack.pop());
token2 = stack.isEmpty() ? null : stack.peek();
}
stack.push(token);
} else if ("(".equals(token)) {
stack.push(token);
} else if (")".equals(token)) {
while (!stack.isEmpty() && !"(".equals(stack.peek())) {
outputQueue.add(stack.pop());
}
if (stack.isEmpty()) {
throw new RuntimeException("Mismatched parentheses");
}
stack.pop();
if (!stack.isEmpty()
&& functions.containsKey(stack.peek().toUpperCase())) {
outputQueue.add(stack.pop());
}
}
}
while (!stack.isEmpty()) {
String element = stack.pop();
if ("(".equals(element) || ")".equals(element)) {
throw new RuntimeException("Mismatched parentheses");
}
if (!operators.containsKey(element)) {
throw new RuntimeException("Unknown operator or function: "
+ element);
}
outputQueue.add(element);
}
return outputQueue;
}
Error
*java.util.EmptyStackException
at java.util.Stack.peek(Unknown Source)
at java.util.Stack.pop(Unknown Source)
at com.business.Expression.eval(Expression.java:1033)*
It is in eval method Object v1 = stack.pop(); line.
Thanks !

In method next you have recursive calls in two places:
after seeing a minus sign
after recognizing an apostrope
The first situation will construct tokens where a minus is followed by a digit (i.e., an unsigend number follows) - OK. (Although, not having a sign but an unary minus operator deserves some consideration.)
The second scenario means trouble. After advancing past the initial apostrophe, another next-result is expected, as if string literals would only contain one number or one identifier or a single operator. Anyway, the next() executes, let's say it returns a number: then an apostroph is added to the token, but there's no effort to check whether there is a closing apostrophe nor to skip that.
else if (ch == '\''){
token.append( '\'' );
pos++;
while( pos < input.length() &&
(ch = input.charAt(pos++)) != '\'' ){
token.append( ch );
}
token.append( '\'' );
This doesn't permit an apostrophe to be a character within the string and it does not diagnose an unterminated string. But this can be added rather easily.

Java Stack Sort Symbol Balancing

The program I am writing has to read a loaded text document and check to see if all the (, [, and { are balanced as well as ignoring anything in between "" and after //. What I have so far checks to see if the first three symbols are all balanced, but I am having trouble with checking the line numbers on which the first occurrence happens. I know that I have to write that if the next symbol is a " or //, I ignore that line or until I hit the next ", but I am unsure of the correct syntax. Any help would be appreciated. Here is what I have so far:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.io.*;
import javax.swing.filechooser.*;
import javax.swing.text.BadLocationException;
public class Sorting extends JFrame implements ActionListener{
private Stack<Character> symbolStack;
JTextArea opentextArea;
JTextArea placetextArea;
JMenuItem open;
final JFileChooser fc = new JFileChooser();
public static void main(String [] args)
{
Sorting gui = new Sorting();
}
public Sorting()
{
JFrame frame = new JFrame();
setLayout(new GridLayout(1,2));
setTitle("Stack Sort");
JMenuBar menuBar = new JMenuBar();
JMenu menuItems = new JMenu("File");
open = new JMenuItem("Open");
open.addActionListener(this);
JMenuItem reset = new JMenuItem("Reset");
reset.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e)
{
opentextArea.setText("");
placetextArea.setText("");
}
}
);
menuItems.add(open);
menuItems.add(reset);
menuBar.add(menuItems);
setJMenuBar(menuBar);
opentextArea = new JTextArea();
placetextArea = new JTextArea();
add(opentextArea);
add(placetextArea);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
setVisible(true);
}
public void actionPerformed(ActionEvent event)
{
int returnVal = fc.showOpenDialog(this);
if (returnVal == JFileChooser.APPROVE_OPTION)
{
File file = fc.getSelectedFile();
FileInputStream is = null;
try
{
is = new FileInputStream(file);
}
catch (FileNotFoundException e)
{
System.out.println("Exception: " + e.toString());
}
byte [] nextChar = new byte[2];
try
{
int value = is.read(nextChar);
int num = 1;
opentextArea.append(num + ":" );
while (value != -1)
{
String newString = new String(nextChar);
if (nextChar[0] == '\n' || nextChar[0] == '\r')
{
num++;
opentextArea.append(newString + num + ":" );
}
else
opentextArea.append(newString);
value = is.read(nextChar);
}
}
catch (IOException e)
{
System.out.println("Exception: " + e.toString());
}
Stack<Character> stack = new Stack<Character>();
String s = opentextArea.getText();
int index = 0;
int numline = 1;
while(index < s.length()) {
char ch = s.charAt(index);
if (ch == '\n' || ch == '\r')
{
numline++;
index++;
}
else
if(ch == '{' || ch == '[' || ch == '(')
{
stack.push(ch);
index++;
}
else {
if(stack.empty())
{
index++;
//placetextArea.append("No balance characters found.");
continue;
}
char ch1 = stack.pop();
if(ch1 == '{' && ch == '}' || ch1 == '[' && ch == ']' || ch1 == '(' && ch == ')')
{
placetextArea.append(ch1 + " at line " +numline + " matches up with " + ch + " at line " + numline + "\n");
}
else
if(ch1 == '{' && ch != '}' || ch1 == '[' && ch != ']' || ch1 == '(' && ch != ')')
{
placetextArea.append("error unmatched " + ch1 + "at line " +numline);
break;
}
}
}
}
}
}
Here is my edited code:
Stack<Character> stack = new Stack<Character>();
String s = opentextArea.getText();
int index = 0;
int numline = 1;
while(index < s.length()) {
char ch = s.charAt(index);
if (ch == '\n' || ch == '\r')
{
numline++;
index++;
}
else
if(ch == '{' || ch == '[' || ch == '(')
{
stack.push(ch);
index++;
}
else {
if(stack.empty())
{
index++;
//placetextArea.append("No balance characters found.");
continue;
}
// pop an item from stack
if(ch == '}' || ch == ']' || ch == ')')
{
char ch1 = stack.pop();
// check if it's a matching pair
if(ch1 == '{' && ch == '}' || ch1 == '[' && ch == ']' || ch1 == '(' && ch == ')')
{
placetextArea.append(ch1 + " at line " +numline + " matches up with " + ch + " at line " + numline + "\n");
}
else
if(ch1 == '{' && ch != '}' || ch1 == '[' && ch != ']' || ch1 == '(' && ch != ')')
{
placetextArea.append("error unmatched " + ch1 + "at line " +numline);
break;
}
}
}
}

You need to pop from the stack only when you encounter one of ), } or ]. Then you check if the closing one matches with the opening. Also you need to define a behavior when it is unmatched: to push the opening back or to drop it. At the EOF you should check if the stack is empty. Otherwise you have something unbalanced.