randomline.java

Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套 代码

// Figure 11.4

import javax.swing.JComponent;
import java.awt.*;
public class RandomLine extends JComponent {
   private int  x1, y1, x2, y2;

	/**	post:	0 <= x1 <= 399  and  0 <= y1 <= 399
	 *			and  0 <= x2 <= 399  and  0 <= y2 <= 399
	 *			and  getBackground() == Color.black  
	 */
	public RandomLine()  {
		setBounds(0, 0, 400, 400);
		x1 = (int)(Math.random()*400);
		x2 = (int)(Math.random()*400);
		y1 = (int)(Math.random()*400);
		y2 = (int)(Math.random()*400);
		setBackground(Color.black);
	}
    
	/**	post:	a black line is drawn from (x1,y1) to (x2,y2)
	 *			and  the line is colored getBackground() 
	 */
	public  void  paint(Graphics g)   {
		g.setColor( getBackground() );
		g.drawLine(x1, y1, x2, y2);
	}
}