学以致用——Java源码——使用随机线段制作屏保程序（Screen Saver for a Random Number of Lines）

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程序功能：

使用随机输出的线段作为屏保程序，用户可随时指定屏幕上要显示的线段数量。

运行示例：

 

源码：

1. 实体类

import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Line2D;
import java.security.SecureRandom;
import javax.swing.JPanel;
import javax.swing.Timer;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;

/**
 * 13.18 (Screen Saver) Write an application that simulates a screen saver. The
 * application should randomly draw lines using method drawLine of class
 * Graphics. After drawing 100 lines, the application should clear itself and
 * start drawing lines again. To allow the program to draw continuously, place a
 * call to repaint as the last line in method paintComponent. Do you notice any
 * problems with this on your system?
 * 
 * 13.19 (Screen Saver Using Timer) Package javax.swing contains a class called
 * Timer that is capable of calling method actionPerformed of interface
 * ActionListener at a fixed time interval (specified in milliseconds). Modify
 * your solution to Exercise 13.18 to remove the call to repaint from method
 * paintComponent. Declare your class to implement ActionListener. (The
 * actionPerformed method should simply call repaint.) Declare an instance
 * variable of type Timer called timer in your class. In the constructor for
 * your class, write the following statements: timer = new Timer(1000, this);
 * timer.start(); This creates an instance of class Timer that will call this
 * object’s actionPerformed method every 1000 milliseconds (i.e., every second).
 * 
 * 13.20 (Screen Saver for a Random Number of Lines) Modify your solution to
 * Exercise 13.19 to enable the user to enter the number of random lines that
 * should be drawn before the application clears itself and starts drawing lines
 * again. Use a JTextField to obtain the value. The user should be able to type
 * a new number into the JTextField at any time during the program’s execution.
 * Use an inner class to perform event handling for the JTextField.
 * 
 * @author [email protected]
 * @Date Jan 23, 2019, 11:26:48 PM
 *
 */
public class ScreenSaverRandomLinesJPanel extends JPanel implements ActionListener
{
	private int lines;	//随机显示的线段数
	
	public ScreenSaverRandomLinesJPanel(int lines) {
		Timer timer = new Timer(1000, this);
		timer.start(); 
		this.lines = lines; //初始化

	}
	public void paint(Graphics g)
	{
	       Graphics2D g2d = (Graphics2D) g;	
		   super.paint(g);
		   double width = getWidth(); // total width   
		   double height = getHeight(); // total height
		   int rRed;
		   int rGreen;
		   int rBlue;
	
		   final SecureRandom rn = new SecureRandom();
		   
		   //画8个同心圆，每个同心圆相距10个像素
		   for (int i = lines; i > 0;i--){
			   //Color represented in RGB mode
			   rRed = rn.nextInt(256);
			   rGreen = rn.nextInt(256);
			   rBlue = rn.nextInt(256);
			   Color color=new Color(rRed, rGreen, rBlue);
			   g2d.setColor(color);	//设置线段颜色
			   
			   double startX = 1+width*rn.nextDouble();
			   double startY = 1+height*rn.nextDouble();
			   double endX = 1+width*rn.nextDouble();
			   double endY = 1+height*rn.nextDouble();
			   float thickness =  (float) 1 + rn.nextInt(20);
			   g2d.setStroke(new BasicStroke(thickness));  //设置线段的粗细
			   g2d.draw(new Line2D.Double(startX, startY, 
					   endX,  endY));	//绘制线段

			   }	


	}
	@Override
	public void actionPerformed(ActionEvent e) {
		// TODO Auto-generated method stub
		repaint();
		
	}
	
	public int getLines() {
		return this.lines;
	}
	
	public void setLines(int lines) {
		this.lines = lines;
	}
		
		
} 

2. 测试类

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JTextField;



public class ScreenSaverRandomLinesTest {

	
	public static void main(String[] args)
	{
	 // create a panel that contains our drawing
	final int LINES = 100;
	 ScreenSaverRandomLinesJPanel panel = new ScreenSaverRandomLinesJPanel(LINES);
	JTextField linesJTextField = new JTextField(String.valueOf(LINES),20);	//要显示的随机线段数
	 linesJTextField.addActionListener(new ActionListener() {	//监听文本框，设置要显示的线段数量
		@Override
		public void actionPerformed(ActionEvent e) {
			panel.setLines(Integer.parseInt(linesJTextField.getText()));
		}
	 });

	 // create a new frame to hold the panel
	 JFrame application = new JFrame();
	 application.setTitle("使用随机线段作为屏保程序");
	 
	 // set the frame to exit when it is closed
	 application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	 application.add(linesJTextField,BorderLayout.SOUTH);	
	 application.add(panel,BorderLayout.CENTER); // add the panel to the frame
	 application.setSize(460, 360); // set the size of the frame
	 application.setVisible(true); // make the frame visible    
	} 
	

	}