A bracket checker

BracketChecker.java

import java.awt.*;
import java.awt.event.*;

public class BracketChecker extends EventPanel implements ActionListener, TextListener {

	private TextField field;
	private Label answerLabel, title, instructions;;

	public BracketChecker(){
		setBackground(Color.white);
		setLayout(null);

		field = new TextField("");
		field.setSize(380,25);
		field.setLocation(10,150);
		field.setBackground(Color.white);
		field.setForeground(Color.black);
		add(field);

		answerLabel = new Label("");
		answerLabel.setSize(400,30);
		answerLabel.setLocation(0,210);
		answerLabel.setAlignment(Label.CENTER);
		answerLabel.setFont(new Font("Serif",Font.BOLD,16));
		answerLabel.setForeground(Color.red);
		add(answerLabel);

		title = new Label ("Bracket Checking Program");
		title.setLocation(0,20);
		title.setSize(400,30);
		title.setFont(new Font("Serif" ,Font.BOLD,20));
		title.setAlignment(Label.CENTER);
		title.setForeground(Color.red);
		add(title);

		instructions = new Label("Press enter to check the expression");
		instructions.setSize(400,30);
		instructions.setLocation(0,120);
		instructions.setAlignment(Label.CENTER);
		instructions.setForeground(Color.red);
		add(instructions);

		field.addActionListener(this);
		field.addTextListener(this);
	}

	public void textValueChanged(TextEvent t ){
		answerLabel.setText("");
	}

	public void actionPerformed(ActionEvent a){
		String s = field.getText();
		CharStack stack = new CharStack();
		IntStack stack2 = new IntStack();
		for(int i =0; i<s.length(); i++){
			char ch = s.charAt(i);
			if("({[<".indexOf(ch)>=0) {
			stack.push(ch);
			stack2.push(i);
		}
		else if (")}]>".indexOf(ch)>=0){
			if(stack.empty()){
				answerLabel.setText("Unmatched Bracket");
				field.setSelectionStart(0);
				field.setSelectionEnd(i+1);
				return;
			}
			char previous = stack.pop();
			int where = stack2.pop();
			if("]})>".indexOf(ch)!="[{(<".indexOf(previous)){
				answerLabel.setText("Brackets don't Match");
				field.setSelectionStart(where);
				field.setSelectionEnd(i+1);
				return;
			}
		}
	}
	if (!stack.empty()){
		//int where = stack2.pop()
		answerLabel.setText("Unmatched Bracket");
		field.setSelectionStart(stack2.pop());
		field.setSelectionEnd(s.length());
	}
	else
		answerLabel.setText("Brackets are good");
	}
}

CharStack.java

public class CharStack {
	private char data[];
	private int top;

	public CharStack(){
		data = new char[100];
		top = -1;
	}
	public void push(char c){
		data[++top] = c;
	}

	public char pop(){
		if(top<0)
		return'(';
		return data[top--];
	}

	public boolean empty(){
		if(top==-1)
			return true;
		return false;
	}
	public char peek(){
		if(top<0)
			return '(';
			return data[top];

	}
}

IntStack.java

public class DoubleStack {
	private double data[];
	private int top;

	public DoubleStack(){
		data = new double[100];
		top = -1;
	}
	public void push(double c){
		data[++top] = c;
	}

	public double pop(){
			return -9999.99;
		return data[top--];

	}

	public boolean empty(){
		if(top==-1)
			return true;
		return false;
	}
}

PanelApplet.java

/*
	 applet that runs a panel
*/

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;

public class PanelApplet extends Applet
{
	BracketCheckerpanel;

	public void init()
	{
		setLayout(null);
		panel = new BracketChecker();
		add(panel);
		panel.setSize(getSize().width, getSize().height);
		panel.setLocation(0,0);
		panel.setVisible(true);
		panel.requestFocus();
		if (panel instanceof KeyListener)
			addKeyListener((KeyListener)panel);
	}
}