enterprice.java

Java 入门书的源码

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

/* Converts the price the user enters in the text field to a 
 * double and adds it to the sum when the user hits the 
 * Enter key or presses the Enter button.  Displays the 
 * average in a label when the user presses the Average button. 
 */

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

public class EnterPrice extends Applet 
                  implements ActionListener {
  private Button average = new Button("Average");
  private Button enter = new Button("Enter Price");
  private TextField text = new TextField(5);
  private Label answer = new Label("Enter prices -- the average goes here");
  private double sum = 0.0;
  private int count = 0; 
  private NumberFormat nf;

  public void init() {
    add(average); 
    add(enter);
    add(text);
    add(answer);
    average.addActionListener(this);
    enter.addActionListener(this);
    text.addActionListener(this);
    nf = NumberFormat.getCurrencyInstance();
  }
  public void actionPerformed(ActionEvent event) {
    Object source = event.getSource();
    if (source == text || source == enter){
      sum += new Double(text.getText()).doubleValue();
      count++;  
      text.setText("");
    }
    else if (source == average) {
      answer.setText("The average is "+ nf.format(sum/count));
    }
  }
}