growthframe.java

Java 入门书的源码

//Copyright (c) 1998, Arthur Gittleman
//This example is provided WITHOUT ANY WARRANTY either expressed or implied.

/* Revises Example 4.5, Growth.java, to make it a graphical
 * rather than a console program.
 */

import java.awt.*;
import java.awt.event.*;
import java.text.NumberFormat;

public class GrowthFrame extends Frame
                        implements ActionListener {
  private TextField getRate = new TextField(5);
  private TextField getBalance = new TextField(8);
  private TextField getYears = new TextField(3);
  private Label rate = new Label("Rate");
  private Label balance = new Label("Balance");
  private Label years = new Label("Years");
  private MyCanvas canvas = new MyCanvas();
  private Button button = new Button("Amount");
  private String amount = "Press button";
  private NumberFormat nf;

  public GrowthFrame(String title) {
    super(title);
    Panel p1 = new Panel();
    p1.setLayout(new GridLayout(2,1));
    p1.add(rate);
    p1.add(getRate); 
    Panel p2 = new Panel();
    p2.setLayout(new GridLayout(2,1));
    p2.add(balance);
    p2.add(getBalance); 
    Panel p3 = new Panel();
    p3.setLayout(new GridLayout(2,1));
    p3.add(years);
    p3.add(getYears);
    Panel p = new Panel();
    p.add(p1);
    p.add(p2);
    p.add(p3);
    Panel p4 = new Panel();
    p4.add(button);
    add(p,"North");
    add(canvas,"Center");
    add(p4,"South"); 
    addWindowListener(new CloseWindow());  
    button.addActionListener(this);
    nf = NumberFormat.getCurrencyInstance();
  } 
  public String computeGrowth() {
    double rate = new Double(getRate.getText()).doubleValue();
    double balance = new Double(getBalance.getText()).doubleValue();
    int years = new Integer(getYears.getText()).intValue();
    for (int i = 1; i <= years; i++)
      balance += balance * rate/100;
    return nf.format(balance);
  }
  public void actionPerformed(ActionEvent event) {
    amount = "The amount is " + computeGrowth();
    canvas.repaint();
  }   
  public static void main(String [] args) {
    GrowthFrame f = new GrowthFrame("Growth");
    f.setSize(300,200);
    f.show(); 
  }
  class CloseWindow extends WindowAdapter {
    public void windowClosing(WindowEvent event) {
      System.exit(0);
    }
  }	
  class MyCanvas extends Canvas {
    public MyCanvas() {
      Font f = new Font("Serif",Font.BOLD,24);
      setFont(f);
    }
    public void paint(Graphics g) {
      g.drawString(amount,10,30); 
    }
  }
}