坦克大战(一期)-完成子弹的可持续发射，并且子弹飞出边界的时候将字段从容器中移除，避免出现内存溢出

src/com/msb/Bullet.java

@@ -15,14 +15,22 @@ public class Bullet extends Frame {
     public static final int WIDTH = 20;
     public static final int HEIGHT = 20;
     public static final int SPEED = 5;
+    private boolean live = true;
+    private TankFrame tankFrame;
 
-    public Bullet(int x, int y, DirEnum dir) {
+    public Bullet(int x, int y, DirEnum dir, TankFrame tankFrame) {
         this.x = x;
         this.y = y;
         this.dir = dir;
+        this.tankFrame = tankFrame;
     }
 
     public void paint(Graphics g) {
+        if( ! this.live)  {
+            tankFrame.bullets.remove(this);
+            return;
+        }
+
         Color color = g.getColor();
         g.setColor(Color.RED);
         g.fillOval(x, y, WIDTH, HEIGHT);
@@ -40,5 +48,7 @@ public class Bullet extends Frame {
             default: break;
         }
 
+        if(x<0 || y<0 || x>TankFrame.GAME_WIDTH || y>TankFrame.GAME_HEIGHT) this.live = false;
+
     }
 }

src/com/msb/Tank.java

@@ -55,6 +55,6 @@ public class Tank {
     }
 
     public void fire() {
-       tankFrame.bullet = new Bullet(this.x, this.y, this.dir);
+       tankFrame.bullets.add(new Bullet(this.x, this.y, this.dir, tankFrame));
     }
 }

src/com/msb/TankFrame.java

@@ -5,6 +5,8 @@ import java.awt.event.KeyAdapter;
 import java.awt.event.KeyEvent;
 import java.awt.event.WindowAdapter;
 import java.awt.event.WindowEvent;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Objects;
 
 /**
@@ -16,7 +18,8 @@ import java.util.Objects;
 public class TankFrame extends Frame {
 
     Tank tank = new Tank(200, 200, DirEnum.RIGHT, this);
-    Bullet bullet = new Bullet(200, 200, DirEnum.DOWN);
+//    Bullet bullet = new Bullet(200, 200, DirEnum.DOWN);
+    List<Bullet> bullets = new ArrayList<>();
     public static final int GAME_WIDTH = 800;
     public static final int GAME_HEIGHT = 600;
 
@@ -42,8 +45,14 @@ public class TankFrame extends Frame {
     @Override
     public void paint(Graphics g) {
 //        super.paint(g);
+        Color color = g.getColor();
+        g.setColor(Color.BLACK);
+        g.drawString("子弹的数量：" + bullets.size(), 10, 60);
+        g.setColor(color);
         tank.paint(g);
-        bullet.paint(g);
+        for (int i=0; i<bullets.size(); i++) {
+            bullets.get(i).paint(g);
+        }
     }
 
     //双缓冲，解决闪烁现象