第二次作业

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class JCalculator extends JFrame implements ActionListener {

    private static final long serialVersionUID = -169068472193786457L;

    private class WindowCloser extends WindowAdapter {

       public void windowClosing(WindowEvent we) {

           System.exit(0);

       }

    }

    int i;

    // Strings for Digit & Operator buttons.

    private final String[] str = { "7", "8", "9", "/", "4", "5", "6", "*", "1",

           "2", "3", "-", ".", "0", "=", "+" };

    // Build buttons.

    JButton[] buttons = new JButton[str.length];

    // For cancel or reset.

    JButton reset = new JButton("CE");

    // Build the text field to show the result.

    JTextField display = new JTextField("0");

    /**

    * Constructor without parameters.

    */

    public JCalculator() {

       super("Calculator");

       // Add a panel.

       JPanel panel1 = new JPanel(new GridLayout(4, 4));

       // panel1.setLayout(new GridLayout(4,4));

       for (i = 0; i < str.length; i++) {

           buttons[i] = new JButton(str[i]);

           panel1.add(buttons[i]);

       }

       JPanel panel2 = new JPanel(new BorderLayout());

       // panel2.setLayout(new BorderLayout());

       panel2.add("Center", display);

       panel2.add("East", reset);

       // JPanel panel3 = new Panel();

       getContentPane().setLayout(new BorderLayout());

       getContentPane().add("North", panel2);

       getContentPane().add("Center", panel1);

       // Add action listener for each digit & operator button.

       for (i = 0; i < str.length; i++)

           buttons[i].addActionListener(this);

       // Add listener for "reset" button.

       reset.addActionListener(this);

       // Add listener for "display" button.

       display.addActionListener(this);

       // The "close" button "X".

       addWindowListener(new WindowCloser());

       // Initialize the window size.

       setSize(800, 800);

       // Show the window.

       // show(); Using show() while JDK version is below 1.5.

       setVisible(true);

       // Fit the certain size.

       pack();

    }  

    public void actionPerformed(ActionEvent e) {

       Object target = e.getSource();

       String label = e.getActionCommand();

       if (target == reset)

           handleReset();

       else if ("0123456789.".indexOf(label) > 0)

           handleNumber(label);

       else

           handleOperator(label);

    }

    // Is the first digit pressed?

    boolean isFirstDigit = true;

    /**

    * Number handling.

    * @param key the key of the button.

    */

    public void handleNumber(String key) {

       if (isFirstDigit)

           display.setText(key);

       else if ((key.equals(".")) && (display.getText().indexOf(".") < 0))

           display.setText(display.getText() + ".");

       else if (!key.equals("."))

           display.setText(display.getText() + key);

       isFirstDigit = false;

    }

    /**

    * Reset the calculator.

    */

    public void handleReset() {

       display.setText("0");

       isFirstDigit = true;

       operator = "=";

    }

    double number = 0.0;

    String operator = "=";

    /**

    * Handling the operation.

    * @param key pressed operator‘s key.

    */

    public void handleOperator(String key) {

       if (operator.equals("+"))

           number += Double.valueOf(display.getText());

       else if (operator.equals("-"))

           number -= Double.valueOf(display.getText());

       else if (operator.equals("*"))

           number *= Double.valueOf(display.getText());

       else if (operator.equals("/"))

           number /= Double.valueOf(display.getText());

       else if (operator.equals("="))

           number = Double.valueOf(display.getText());

       display.setText(String.valueOf(number));

       operator = key;

       isFirstDigit = true;

    }

    public static void main(String[] args) {

       new JCalculator();

    }

}