Swing I - Absolute Java - page 1002

Display 17.19 A Simple Calculator (part 1 of 4)

1 import javax.swing.JFrame;
2 import javax.swing.JTextField;
3 import javax.swing.JPanel;
4 import javax.swing.JLabel;
5 import javax.swing.JButton;
6 import java.awt.BorderLayout;
7 import java.awt.FlowLayout;
8 import java.awt.Color;
9 import java.awt.event.ActionListener;
10 import java.awt.event.ActionEvent;

11 /**
12 A simplified calculator.
13 The only operations are addition and subtraction.
14 */
15 public class Calculator extends JFrame
16 implements ActionListener

17 {
18

public static final int WIDTH = 400;

19 public static final int HEIGHT = 200;

20 public static final int NUMBER_OF_DIGITS = 30;

21 private JTextField ioField;

22 private double result = 0.0;

23 public static void main(String[] args)
24 {
25 Calculator aCalculator = new Calculator();
26 aCalculator.setVisible( true );
27 }

28 public Calculator()
29 {
30 setTitle("Simplified Calculator");
31 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
32 setSize(WIDTH, HEIGHT);
33 setLayout( new BorderLayout());

34 JPanel textPanel = new JPanel();
35 textPanel.setLayout( new FlowLayout());
36 ioField =
37 new JTextField("Enter numbers here.",NUMBER_OF_DIGITS);
38 ioField.setBackground(Color.WHITE);
39 textPanel.add(ioField);
40 add(textPanel, BorderLayout.NORTH);
41 JPanel buttonPanel = new JPanel();
42 buttonPanel.setBackground(Color.BLUE);
43 buttonPanel.setLayout( new FlowLayout());