HANDLING EXCEPTIONS AND EVENTS - Java Programming: From Problem Analysis to Program Design - page 773

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;

public class Calculator extends JFrame implements
ActionListener

{

private JTextField displayText = new JTextField(30);
private JButton[] button = new JButton[16];

private String[] keys = {"7", "8", "9", "/",
"4", "5", "6", "*",
"1", "2", "3", "-",
"0", "C", "=", "+"};

private String numStr1 = "";
private String numStr2 = "";

private char op;
private boolean firstInput = true ;

public Calculator()
{

setTitle("My Calculator");
setSize(230, 200);
Container pane = getContentPane();

pane.setLayout( null );

displayText.setSize(200,30);
displayText.setLocation(10,10);
pane.add(displayText);

1
1

int x, y;

x = 10;
y = 40;

for ( int ind = 0; ind < 16; ind++)
{

button[ind] = new JButton(keys[ind]);
button[ind].addActionListener( this );
button[ind].setSize(50,30);
button[ind].setLocation(x, y);
pane.add(button[ind]);
x = x + 50;

if ((ind + 1) % 4 == 0)
{

x = 10;
y = y + 30;

}

}