driver.java

来自「Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套」· Java 代码 · 共 50 行

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

/** Program to animate a message moving side to side in a window  (Figure 8.38)
 *  Author: David Riley
 *  Date: January, 2005 
 */
public class Driver  {
	private JFrame window;
	private Label fishyMsg;
	private MsgCallbackTimer clock;
	private int velocity;

	/**	post:	window != null 
	 *				and fishyMsg is placed at the left edge of window
	 *				and velocity = 2
	 *				and clock is scheduled for 1/50 sec. repeated events 
	 */
	public Driver()   {
		window = new JFrame("Animated Message");
		window.setBounds(10, 10, 400, 200);
		window.setVisible(true);
		window.setLayout(null);
		fishyMsg = new Label("FISH");
		fishyMsg.setBounds(0, 70, 50, 30);
		fishyMsg.setForeground(Color.black);
		fishyMsg.setBackground(Color.blue);
		window.add(fishyMsg, 0); 
		window.repaint();
		velocity = 1;
		clock = new MsgCallbackTimer(20, this);
		clock.start();
	}

	/**	pre:	fishyMsg != null  <br>
	 *		post:	(either the left or right edge of fishyMsg@pre lies
	 *				outside the boundaries of pane)  
	 *  						implies velocity == - velocity@pre
	 *				and  fishyMsg.getX() == fishyMsg.getX()@pre + velocity 
	 */
	public void moveMsg( )   {
		if (fishyMsg.getX() < 0
			|| fishyMsg.getX()+fishyMsg.getWidth() > window.getWidth())
		{
			velocity = -velocity;
		}
		fishyMsg.setLocation( fishyMsg.getX()+velocity, fishyMsg.getY() );
	}
}