helloframe.java

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package hello;

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

//应用implements关键字引入KeyListener键盘接收器
public class HelloFrame extends JFrame implements java.awt.event.KeyListener{
  private static final String WINDOWTITLE = "Hello窗口程序";
  JPanel contentPane;
  BorderLayout borderLayout1 = new BorderLayout();
  String showStr = "";

  //当窗口关闭时清空内存
  protected void processWindowEvent(WindowEvent e) {
    if (e.getID() == WindowEvent.WINDOW_CLOSING) {
      System.exit(0);
    }
  }

  //打开窗口的主方法
  public static void main(String[] args) {
    HelloFrame frame = new HelloFrame();
    //取得屏幕大小    
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    //取得窗口大小
    Dimension frameSize = frame.getSize();
    //使窗口居中对齐
    frame.setLocation( (screenSize.width - frameSize.width) / 2,
                       (screenSize.height - frameSize.height) / 2);
    frame.setVisible(true);
  }
  
  //类的构造器
  public HelloFrame() {
    try {
      initialize();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }

  //初始化窗口的方法
  private void initialize() throws Exception  {
    contentPane = (JPanel) this.getContentPane();
    contentPane.setLayout(borderLayout1);
    this.setSize(new Dimension(400, 300));
    this.setTitle(WINDOWTITLE);
    //为窗口面板加入键盘接收器
    this.addKeyListener(this);
  }

  public String getShowStr() {
    return showStr;
  }

  public void setShowStr(String showStr) {
    this.showStr = showStr;
  }

  public void keyPressed(KeyEvent e) {
    //取得输入的字符
    char c = e.getKeyChar(); 
    if(c == 'a'){
      JOptionPane.showMessageDialog(null, "用户按下a键。");
    }
  }
  
  public void keyReleased(KeyEvent e) {}
  
  public void keyTyped(KeyEvent e) {}
}