ball.java

自己写的弹球程序～～比较适合初学者去看～～

package day03.ball;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;

/**
 * 小球类，代表在画布上移动的小球
 * @author Administrator
 *
 */
public class Ball{
	   private BallPanel canvas;//画布
	   private Color color;//小球的颜色
	   private static final int XSIZE = 30;//小球的X直径
	   private static final int YSIZE = 30;//小球的Y直径
	   private int x = 0;  //小球所处的座标  
	   private int y = 0;    
	   private int dx = 1;  //小球每次移动的步长  
	   private int dy = 1;
	   public static int CURRENT_NUM=1;//当前小球的编号
	   
	   private int number;//该小球的编号
	   
	   public Ball(BallPanel c) { 
		   this(c,Color.black); 
	   }
	   
	   public Ball(BallPanel c, Color color) {
		   canvas = c; 
		   this.color = color;
		   this.number=CURRENT_NUM;
		   CURRENT_NUM++;
	   }
	   
	   /**
	    * 根据x，y座标绘制当前小球
	    * @param g2
	    */
	   public void draw(Graphics2D g2) { 
		   if(color != null) g2.setColor(color); 
		   g2.fill(new Ellipse2D.Double(x, y, XSIZE, YSIZE)); 
		   g2.setColor(Color.WHITE);
		   g2.setFont(new Font("",Font.BOLD,16));
		   g2.drawString(number+"", x+XSIZE/2-5, y+YSIZE/2+5);
	   }
   
	   /**
	    * 该方法控制小球的移动动作。
	    * 移动小球其实就是把小球的座标位置改变一下，
	    * 再调用画布的repaint方法。
	    *
	    */
	   public void move(){
		   x += dx;  y += dy;
		   if (x < 0){  x = 0;   dx = -dx;   }
		   if (x + XSIZE >= canvas.getWidth()){ x = canvas.getWidth() - XSIZE; dx = -dx; }
		   if (y < 0){  y = 0;  dy = -dy; }
		   if (y + YSIZE >= canvas.getHeight()) { y = canvas.getHeight() - YSIZE; dy = -dy;  }
		   canvas.repaint();
	   }

	public BallPanel getCanvas() {
		return canvas;
	}
	   
	   
}