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实现了坦克的移动，现在要实现坦克可以打出炮弹：

功能：添加子弹类，添加方法和参数。

1.位置和方向属性

int x,y; Tank.Direction dir;

2.构造方法

public Missile(int x, int y,Tank.Direction dir) {		this.x = x;		this.y = y;		this.dir=dir;	}

3.画坦克的方法

public void draw(Graphics g){		Color c = g.getColor();		g.setColor(Color.BLACK);		g.fillOval(x, y, 10, 10);		g.setColor(c);				move();	}

private void move(){		switch(dir){		case L: x -= XSPEED;break;		case LU: x -= XSPEED; y -= XSPEED;break;		case U: y -= XSPEED;break;		case RU: x += XSPEED;y -= XSPEED;break;		case R: x += XSPEED;break;		case RD: x += XSPEED;y += XSPEED;break;		case D: y += XSPEED;break;		case LD: x -= XSPEED;y += XSPEED;break;		   }	   	   }

设置速度

public static final int XSPEED =10;  public static final int YSPEED =10;

5.测试：

在主类里面创建对象

Tank myTank = new Tank(50, 50);    Missile ms = new Missile(100, 100, Tank.Direction.RD);    Image offScreenImage = null;        public void paint(Graphics g) {        ms.draw(g);        myTank.draw(g);            }

public class Missile {    	        public static final int XSPEED =10;        public static final int YSPEED =10;    	        int x,y;        Tank.Direction dir;            	public Missile(int x, int y,Tank.Direction dir) {		this.x = x;		this.y = y;		this.dir=dir;	}    	public void draw(Graphics g){		Color c = g.getColor();		g.setColor(Color.BLACK);		g.fillOval(x, y, 10, 10);		g.setColor(c);				move();	}		private void move(){		switch(dir){		case L: x -= XSPEED;break;		case LU: x -= XSPEED; y -= XSPEED;break;		case U: y -= XSPEED;break;		case RU: x += XSPEED;y -= XSPEED;break;		case R: x += XSPEED;break;		case RD: x += XSPEED;y += XSPEED;break;		case D: y += XSPEED;break;		case LD: x -= XSPEED;y += XSPEED;break;		   }	   	   }}

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