diff --git a/docs/坦克大战笔记.docx b/docs/坦克大战笔记.docx
index e411e9b..e0753c6 100644
Binary files a/docs/坦克大战笔记.docx and b/docs/坦克大战笔记.docx differ
diff --git a/src/com/demo/tank/course8/Tank.java b/src/com/demo/tank/course8/Tank.java
index 9a4331b..7ecda1a 100644
--- a/src/com/demo/tank/course8/Tank.java
+++ b/src/com/demo/tank/course8/Tank.java
@@ -9,6 +9,7 @@ import java.util.Random;
 
 public class Tank extends GameObject{
     private int x,y;
+    int oldX, oldY;
     private Direction dir;
     private static final int SPEED = 8;
     private boolean moving = true;
@@ -70,6 +71,8 @@ public class Tank extends GameObject{
     }
 
     public void move(){
+        oldX = x;
+        oldY = y;
         //如果没有移动 return
         if(!moving) return;
         switch (dir){
@@ -100,6 +103,11 @@ public class Tank extends GameObject{
         rect.y = this.y;
     }
 
+    public void back(){
+        this.x = oldX;
+        this.y = oldY;
+    }
+
     private void boundsCheck() {
         if(x < 0) x = 0;
         if(x > TankFrameV8.GAME_WIDTH - Tank.WIDTH) x = TankFrameV8.GAME_WIDTH - Tank.WIDTH;
diff --git a/src/com/demo/tank/course8/TankTankCollider.java b/src/com/demo/tank/course8/TankTankCollider.java
index 33682a8..64930ae 100644
--- a/src/com/demo/tank/course8/TankTankCollider.java
+++ b/src/com/demo/tank/course8/TankTankCollider.java
@@ -13,8 +13,8 @@ public class TankTankCollider implements Collider{
             Tank t2 = (Tank) g2;
             if(t1.rect.intersects(t2.rect)){
                 // simple deal
-                t1.setDir(Direction.values()[random.nextInt(4)]);
-                t2.setDir(Direction.values()[random.nextInt(4)]);
+                t1.back();
+                t2.back();
             }
         }else{
             return;
diff --git a/src/com/demo/tank/course9/Bullet.java b/src/com/demo/tank/course9/Bullet.java
new file mode 100644
index 0000000..902efe2
--- /dev/null
+++ b/src/com/demo/tank/course9/Bullet.java
@@ -0,0 +1,117 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Direction;
+import com.demo.tank.enums.Group;
+import com.demo.tank.util.ResourceManager;
+
+import java.awt.*;
+
+public class Bullet extends GameObject {
+    private int x, y;
+    private Direction direction;
+    private static final int SPEED = 10;
+    public static final int WIDTH = ResourceManager.bulletD.getWidth();
+    public static final int HEIGHT = ResourceManager.bulletD.getHeight();
+    private boolean live = true;
+    private Group group = Group.BAD;
+    Rectangle rect = new Rectangle();
+
+    public Bullet(int x, int y, Direction direction, Group group) {
+        this.x = x;
+        this.y = y;
+        this.direction = direction;
+        this.group = group;
+
+        rect.x = this.x;
+        rect.y = this.y;
+        rect.width = Bullet.WIDTH;
+        rect.height = Bullet.HEIGHT;
+        GameModel.getInstance().add(this);
+    }
+
+    public void paint(Graphics g){
+        if(!live){
+            GameModel.getInstance().remove(this);
+        }
+        switch (direction){
+            case UP:
+                g.drawImage(ResourceManager.bulletU, x, y, null);
+                break;
+            case DOWN:
+                g.drawImage(ResourceManager.bulletD, x, y, null);
+                break;
+            case LEFT:
+                g.drawImage(ResourceManager.bulletL, x, y, null);
+                break;
+            case RIGHT:
+                g.drawImage(ResourceManager.bulletR, x, y, null);
+                break;
+        }
+        move();
+    }
+
+    private void move() {
+        switch (direction){
+            case UP: y -= SPEED;
+                break;
+            case DOWN: y += SPEED;
+                break;
+            case LEFT: x -= SPEED;
+                break;
+            case RIGHT: x += SPEED;
+                break;
+            default:
+                break;
+        }
+        if(x < 0 || y < 0 || x > TankFrameV9.GAME_WIDTH || y > TankFrameV9.GAME_HEIGHT){
+            live = false;
+        }
+        rect.x = this.x;
+        rect.y = this.y;
+    }
+
+    public void die() {
+        this.live = false;
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    public void setY(int y) {
+        this.y = y;
+    }
+
+    public Direction getDirection() {
+        return direction;
+    }
+
+    public void setDirection(Direction direction) {
+        this.direction = direction;
+    }
+
+    public boolean isLive() {
+        return live;
+    }
+
+    public void setLive(boolean live) {
+        this.live = live;
+    }
+
+    public Group getGroup() {
+        return group;
+    }
+
+    public void setGroup(Group group) {
+        this.group = group;
+    }
+
+}
diff --git a/src/com/demo/tank/course9/BulletTankCollider.java b/src/com/demo/tank/course9/BulletTankCollider.java
new file mode 100644
index 0000000..d943f8f
--- /dev/null
+++ b/src/com/demo/tank/course9/BulletTankCollider.java
@@ -0,0 +1,25 @@
+package com.demo.tank.course9;
+
+public class BulletTankCollider implements Collider {
+    @Override
+    public void collide(GameObject g1, GameObject g2) {
+        if(g1 instanceof Bullet && g2 instanceof Tank){
+            Bullet b = (Bullet) g1;
+            Tank t = (Tank) g2;
+            //关闭队友伤害
+            if(b.getGroup() == t.getGroup()) return;
+            if(b.rect.intersects(t.rect)){
+                t.die();
+                b.die();
+                //爆炸
+                int ex = t.getX() + Tank.WIDTH/2 - Explode.WIDTH/2;
+                int ey = t.getY() + Tank.HEIGHT/2 - Explode.HEIGHT/2;
+                GameModel.getInstance().add(new Explode(ex, ey));
+            }
+        }else if(g1 instanceof Tank && g2 instanceof Bullet){
+            collide(g2, g1);
+        }else{
+            return;
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/BulletWallCollider.java b/src/com/demo/tank/course9/BulletWallCollider.java
new file mode 100644
index 0000000..3071f20
--- /dev/null
+++ b/src/com/demo/tank/course9/BulletWallCollider.java
@@ -0,0 +1,18 @@
+package com.demo.tank.course9;
+
+public class BulletWallCollider implements Collider {
+    @Override
+    public void collide(GameObject g1, GameObject g2) {
+        if(g1 instanceof Bullet && g2 instanceof Wall){
+            Bullet b = (Bullet) g1;
+            Wall w = (Wall) g2;
+            if(b.rect.intersects(w.rect)){
+                b.die();
+            }
+        }else if(g1 instanceof Wall && g2 instanceof Bullet){
+            collide(g2, g1);
+        }else{
+            return;
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/Collider.java b/src/com/demo/tank/course9/Collider.java
new file mode 100644
index 0000000..7ab6d92
--- /dev/null
+++ b/src/com/demo/tank/course9/Collider.java
@@ -0,0 +1,5 @@
+package com.demo.tank.course9;
+
+public interface Collider {
+    void collide(GameObject g1, GameObject g2);
+}
diff --git a/src/com/demo/tank/course9/ColliderChain.java b/src/com/demo/tank/course9/ColliderChain.java
new file mode 100644
index 0000000..3ed6a94
--- /dev/null
+++ b/src/com/demo/tank/course9/ColliderChain.java
@@ -0,0 +1,25 @@
+package com.demo.tank.course9;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class ColliderChain {
+    private List<Collider> colliders = new LinkedList<>();
+
+    public ColliderChain(){
+        add(new BulletTankCollider());
+        add(new TankTankCollider());
+        add(new BulletWallCollider());
+        add(new TankWallCollider());
+    }
+
+    public void add(Collider collider){
+        colliders.add(collider);
+    }
+
+    public void collide(GameObject g1, GameObject g2) {
+        for (Collider c : colliders){
+            c.collide(g1, g2);
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/DefaultFireStrategy.java b/src/com/demo/tank/course9/DefaultFireStrategy.java
new file mode 100644
index 0000000..ec2d86d
--- /dev/null
+++ b/src/com/demo/tank/course9/DefaultFireStrategy.java
@@ -0,0 +1,14 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Group;
+import com.demo.tank.util.Audio;
+
+public class DefaultFireStrategy implements FireStrategy {
+    @Override
+    public void fire(Tank tank) {
+        int bx = tank.getX() + Tank.WIDTH/2 - Bullet.WIDTH/2;
+        int by = tank.getY() + Tank.HEIGHT/2 - Bullet.HEIGHT/2;
+        new Bullet(bx, by, tank.getDir(), tank.getGroup());
+        if (tank.getGroup() == Group.GOOD) new Thread(() -> new Audio("audio/tank_fire.wav").play()).start();
+    }
+}
diff --git a/src/com/demo/tank/course9/Explode.java b/src/com/demo/tank/course9/Explode.java
new file mode 100644
index 0000000..3a8c16d
--- /dev/null
+++ b/src/com/demo/tank/course9/Explode.java
@@ -0,0 +1,45 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.util.Audio;
+import com.demo.tank.util.ResourceManager;
+
+import java.awt.*;
+
+public class Explode extends GameObject {
+    private int x, y;
+    public static final int WIDTH = ResourceManager.explodes[0].getWidth();
+    public static final int HEIGHT = ResourceManager.explodes[0].getHeight();
+
+    private int step = 0;
+
+    public Explode(int x, int y) {
+        this.x = x;
+        this.y = y;
+        new Thread(() -> new Audio("audio/explode.wav").play()).start();
+    }
+
+    public void paint(Graphics g){
+        g.drawImage(ResourceManager.explodes[step++], x, y, null);
+        if(step >= ResourceManager.explodes.length){
+            //播放完爆炸效果图片， remove
+            GameModel.getInstance().remove(this);
+        }
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    public void setY(int y) {
+        this.y = y;
+    }
+
+}
diff --git a/src/com/demo/tank/course9/FireStrategy.java b/src/com/demo/tank/course9/FireStrategy.java
new file mode 100644
index 0000000..e2c0e41
--- /dev/null
+++ b/src/com/demo/tank/course9/FireStrategy.java
@@ -0,0 +1,5 @@
+package com.demo.tank.course9;
+
+public interface FireStrategy {
+    void fire(Tank tank);
+}
diff --git a/src/com/demo/tank/course9/FourDirectionFireStrategy.java b/src/com/demo/tank/course9/FourDirectionFireStrategy.java
new file mode 100644
index 0000000..0b508d1
--- /dev/null
+++ b/src/com/demo/tank/course9/FourDirectionFireStrategy.java
@@ -0,0 +1,17 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Direction;
+import com.demo.tank.enums.Group;
+import com.demo.tank.util.Audio;
+
+public class FourDirectionFireStrategy implements FireStrategy {
+    @Override
+    public void fire(Tank tank) {
+        int bx = tank.getX() + Tank.WIDTH/2 - Bullet.WIDTH/2;
+        int by = tank.getY() + Tank.HEIGHT/2 - Bullet.HEIGHT/2;
+        for(Direction direction : Direction.values()){
+            new Bullet(bx, by, direction, tank.getGroup());
+        }
+        if (tank.getGroup() == Group.GOOD) new Thread(() -> new Audio("audio/tank_fire.wav").play()).start();
+    }
+}
diff --git a/src/com/demo/tank/course9/GameModel.java b/src/com/demo/tank/course9/GameModel.java
new file mode 100644
index 0000000..1e05609
--- /dev/null
+++ b/src/com/demo/tank/course9/GameModel.java
@@ -0,0 +1,67 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Direction;
+import com.demo.tank.enums.Group;
+import com.demo.tank.util.PropertyManager;
+
+import java.awt.*;
+import java.util.ArrayList;
+import java.util.List;
+
+public class GameModel {
+    private static final GameModel GM = new GameModel();
+    static {
+        GM.init();
+    }
+
+    private List<GameObject> gameObjects = new ArrayList<>();
+
+//    Collider collider = new BulletTankCollider();
+//    Collider collider2 = new TankTankCollider();
+    ColliderChain chain = new ColliderChain();
+    Tank tank;
+
+    private GameModel(){
+
+    }
+    private void init(){
+        tank = new Tank(380, 660, Direction.UP, Group.GOOD);
+        int enemyTankNum = PropertyManager.getInt("enemy.tank.number");
+        for(int i = 0; i < enemyTankNum; i++){
+            add(new Tank(50 + i*80, 200, Direction.DOWN, Group.BAD));
+        }
+        add(new Wall(150, 150, 200, 50));
+        add(new Wall(550, 150, 200, 50));
+        add(new Wall(300, 300, 50, 200));
+        add(new Wall(550, 300, 50, 200));
+    }
+
+    public static GameModel getInstance(){
+        return GM;
+    }
+
+    public void add(GameObject go){
+        gameObjects.add(go);
+    }
+
+    public void remove(GameObject go){
+        gameObjects.remove(go);
+    }
+
+    public void paint(Graphics g){
+        tank.paint(g);
+
+        for(int i = 0; i< gameObjects.size(); i++){
+            gameObjects.get(i).paint(g);
+        }
+
+        //碰撞检测
+        for(int i = 0; i< gameObjects.size(); i++){
+            for(int j=i+1; j< gameObjects.size(); j++){
+               GameObject g1 = gameObjects.get(i);
+               GameObject g2 = gameObjects.get(j);
+               chain.collide(g1, g2);
+            }
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/GameObject.java b/src/com/demo/tank/course9/GameObject.java
new file mode 100644
index 0000000..21dce58
--- /dev/null
+++ b/src/com/demo/tank/course9/GameObject.java
@@ -0,0 +1,8 @@
+package com.demo.tank.course9;
+
+import java.awt.*;
+
+public abstract class GameObject {
+    int x, y;
+    public abstract void paint(Graphics g);
+}
diff --git a/src/com/demo/tank/course9/MainV9.java b/src/com/demo/tank/course9/MainV9.java
new file mode 100644
index 0000000..38064b2
--- /dev/null
+++ b/src/com/demo/tank/course9/MainV9.java
@@ -0,0 +1,16 @@
+package com.demo.tank.course9;
+
+import java.io.IOException;
+
+public class MainV9 {
+    public static void main(String[] args) throws InterruptedException, IOException {
+        TankFrameV9 tf = new TankFrameV9();
+
+//        new Thread(() -> new Audio("audio/war1.wav").loop()).start();
+
+        while (true){
+            Thread.sleep(50);
+            tf.repaint();
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/Tank.java b/src/com/demo/tank/course9/Tank.java
new file mode 100644
index 0000000..2e36d22
--- /dev/null
+++ b/src/com/demo/tank/course9/Tank.java
@@ -0,0 +1,184 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Direction;
+import com.demo.tank.enums.Group;
+import com.demo.tank.util.ResourceManager;
+
+import java.awt.*;
+import java.util.Random;
+
+public class Tank extends GameObject {
+    private int x,y;
+    int oldX, oldY;
+    private Direction dir;
+    private static final int SPEED = 8;
+    private boolean moving = true;
+    private boolean living = true;
+    private Group group = Group.BAD;
+    public static final int WIDTH = ResourceManager.tankD.getWidth();
+    public static final int HEIGHT = ResourceManager.tankD.getHeight();
+    private Random random = new Random();
+    Rectangle rect = new Rectangle();
+    FireStrategy fireStrategy;
+
+
+    public Tank(int x, int y, Direction dir, Group group) {
+        this.x = x;
+        this.y = y;
+        this.dir = dir;
+        this.group = group;
+
+        rect.x = this.x;
+        rect.y = this.y;
+        rect.width = Tank.WIDTH;
+        rect.height = Tank.HEIGHT;
+
+        if(this.group == Group.GOOD) {
+//            String className = PropertyManager.getString("good.tank.fire.strategy");
+            try {
+                fireStrategy = (FireStrategy) Class.forName("com.demo.tank.course9.FourDirectionFireStrategy").newInstance();
+            } catch (ClassNotFoundException e) {
+                e.printStackTrace();
+            } catch (InstantiationException e) {
+                e.printStackTrace();
+            } catch (IllegalAccessException e) {
+               e.printStackTrace();
+            }
+        }else if(this.group == Group.BAD) fireStrategy = new DefaultFireStrategy();
+    }
+
+    @Override
+    public void paint(Graphics g) {
+        if(!living) GameModel.getInstance().remove(this);
+        //根据方向绘制坦克
+        switch (dir){
+            case UP:
+                g.drawImage(this.group == Group.GOOD ? ResourceManager.tankU : ResourceManager.badTankU, x, y, null);
+            break;
+            case DOWN:
+                g.drawImage(this.group == Group.GOOD ? ResourceManager.tankD : ResourceManager.badTankD, x, y, null);
+                break;
+            case LEFT:
+                g.drawImage(this.group == Group.GOOD ? ResourceManager.tankL: ResourceManager.badTankL, x, y, null);
+                break;
+            case RIGHT:
+                g.drawImage(this.group == Group.GOOD ? ResourceManager.tankR : ResourceManager.badTankR, x, y, null);
+                break;
+        }
+        move();
+    }
+
+    public void move(){
+        oldX = x;
+        oldY = y;
+        //如果没有移动 return
+        if(!moving) return;
+        switch (dir){
+            case UP: y -= SPEED;
+                break;
+            case DOWN: y += SPEED;
+                break;
+            case LEFT: x -= SPEED;
+                break;
+            case RIGHT: x += SPEED;
+                break;
+            default:
+                break;
+        }
+        if(this.group == Group.BAD) {
+            if(random.nextInt(10) == 5){
+                this.fire();
+            }
+            if(random.nextInt(100) > 95){
+                this.randomDirection();
+            }
+        }
+
+        //边界检测
+        boundsCheck();
+
+        rect.x = this.x;
+        rect.y = this.y;
+    }
+
+    public void back(){
+        this.x = oldX;
+        this.y = oldY;
+    }
+
+    private void boundsCheck() {
+        if(x < 0) x = 0;
+        if(x > TankFrameV9.GAME_WIDTH - Tank.WIDTH) x = TankFrameV9.GAME_WIDTH - Tank.WIDTH;
+        if(y < 30) y = 30; //算上菜单条
+        if(y > TankFrameV9.GAME_HEIGHT - Tank.HEIGHT) y = TankFrameV9.GAME_HEIGHT - Tank.HEIGHT;
+    }
+
+    private void randomDirection() {
+          this.dir = Direction.values()[random.nextInt(4)];
+    }
+
+    public void fire() {
+       fireStrategy.fire(this);
+    }
+
+    public void die(){
+        this.living = false;
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    public void setY(int y) {
+        this.y = y;
+    }
+
+    public Direction getDir() {
+        return dir;
+    }
+
+    public void setDir(Direction dir) {
+        this.dir = dir;
+    }
+
+    public boolean isMoving() {
+        return moving;
+    }
+
+    public void setMoving(boolean moving) {
+        this.moving = moving;
+    }
+
+    public boolean isLiving() {
+        return living;
+    }
+
+    public void setLiving(boolean living) {
+        this.living = living;
+    }
+
+    public Group getGroup() {
+        return group;
+    }
+
+    public void setGroup(Group group) {
+        this.group = group;
+    }
+
+    public Rectangle getRect() {
+        return rect;
+    }
+
+    public void setRect(Rectangle rect) {
+        this.rect = rect;
+    }
+
+}
diff --git a/src/com/demo/tank/course9/TankFrameV9.java b/src/com/demo/tank/course9/TankFrameV9.java
new file mode 100644
index 0000000..29ec300
--- /dev/null
+++ b/src/com/demo/tank/course9/TankFrameV9.java
@@ -0,0 +1,113 @@
+package com.demo.tank.course9;
+
+import com.demo.tank.enums.Direction;
+
+import java.awt.*;
+import java.awt.event.KeyAdapter;
+import java.awt.event.KeyEvent;
+import java.awt.event.WindowAdapter;
+import java.awt.event.WindowEvent;
+
+public class TankFrameV9 extends Frame {
+    GameModel gm = GameModel.getInstance();
+    public static final int GAME_WIDTH = 1080;
+    public static final int GAME_HEIGHT = 800;
+    Image image = null;
+
+    public TankFrameV9(){
+        setVisible(true);
+        setBounds(400, 100 , GAME_WIDTH, GAME_HEIGHT);
+        setResizable(false);
+        setTitle("tank war");
+        this.addKeyListener(new MyKeyListener());
+        this.addWindowListener(new WindowAdapter() {
+            @Override
+            public void windowClosing(WindowEvent e) {
+                System.exit(0);
+            }
+        });
+    }
+
+    @Override
+    public void update(Graphics g) {
+        if(image == null){
+            image = this.createImage(GAME_WIDTH, GAME_HEIGHT);
+        }
+        Graphics imgGraphic =  image.getGraphics();
+        Color color = g.getColor();
+        imgGraphic.setColor(Color.BLACK);
+        imgGraphic.fillRect(0,0, GAME_WIDTH, GAME_HEIGHT);
+        imgGraphic.setColor(color);
+        paint(imgGraphic);
+        g.drawImage(image, 0, 0, null);
+    }
+
+    @Override
+    public void paint(Graphics g){
+        gm.paint(g);
+    }
+
+    class MyKeyListener extends KeyAdapter{
+        boolean bL = false;
+        boolean bR = false;
+        boolean bU = false;
+        boolean bD = false;
+
+        @Override
+        public void keyPressed(KeyEvent e) {
+            switch (e.getKeyCode()){
+                case KeyEvent.VK_A:
+                    bL = true;
+                    break;
+                case KeyEvent.VK_D:
+                    bR = true;
+                    break;
+                case KeyEvent.VK_W:
+                        bU = true;
+                        break;
+                case KeyEvent.VK_S:
+                    bD = true;
+                    break;
+                default:
+                    break;
+            }
+            setTankDirection();
+        }
+
+        @Override
+        public void keyReleased(KeyEvent e) {
+            switch (e.getKeyCode()){
+                case KeyEvent.VK_A:
+                    bL = false;
+                    break;
+                case KeyEvent.VK_D:
+                    bR = false;
+                    break;
+                case KeyEvent.VK_W:
+                    bU = false;
+                    break;
+                case KeyEvent.VK_S:
+                    bD = false;
+                    break;
+                case KeyEvent.VK_SPACE:
+                    gm.tank.fire();
+                    break;
+                default:
+                    break;
+            }
+            setTankDirection();
+        }
+
+        public void setTankDirection(){
+            if(!bL && !bR && !bU && !bD){
+                gm.tank.setMoving(false);
+            }else{
+                gm.tank.setMoving(true);
+                if(bL) gm.tank.setDir(Direction.LEFT);
+                if(bR) gm.tank.setDir(Direction.RIGHT);
+                if(bU) gm.tank.setDir(Direction.UP);
+                if(bD) gm.tank.setDir(Direction.DOWN);
+            }
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/TankTankCollider.java b/src/com/demo/tank/course9/TankTankCollider.java
new file mode 100644
index 0000000..310016a
--- /dev/null
+++ b/src/com/demo/tank/course9/TankTankCollider.java
@@ -0,0 +1,21 @@
+package com.demo.tank.course9;
+
+import java.util.Random;
+
+public class TankTankCollider implements Collider {
+    Random random = new Random();
+    @Override
+    public void collide(GameObject g1, GameObject g2) {
+        if(g1 instanceof Tank && g2 instanceof Tank){
+            Tank t1 = (Tank) g1;
+            Tank t2 = (Tank) g2;
+            if(t1.rect.intersects(t2.rect)){
+                // simple deal
+                t1.back();
+                t2.back();
+            }
+        }else{
+            return;
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/TankWallCollider.java b/src/com/demo/tank/course9/TankWallCollider.java
new file mode 100644
index 0000000..773713d
--- /dev/null
+++ b/src/com/demo/tank/course9/TankWallCollider.java
@@ -0,0 +1,18 @@
+package com.demo.tank.course9;
+
+public class TankWallCollider implements Collider{
+    @Override
+    public void collide(GameObject g1, GameObject g2) {
+        if(g1 instanceof Tank && g2 instanceof Wall){
+            Tank t = (Tank) g1;
+            Wall w = (Wall) g2;
+            if(t.rect.intersects(w.rect)){
+                t.back();
+            }
+        }else if(g1 instanceof Wall && g2 instanceof Bullet){
+            collide(g2, g1);
+        }else{
+            return;
+        }
+    }
+}
diff --git a/src/com/demo/tank/course9/Wall.java b/src/com/demo/tank/course9/Wall.java
new file mode 100644
index 0000000..60910db
--- /dev/null
+++ b/src/com/demo/tank/course9/Wall.java
@@ -0,0 +1,24 @@
+package com.demo.tank.course9;
+
+import java.awt.*;
+
+public class Wall extends GameObject{
+    int width, height;
+    Rectangle rect;
+
+    public Wall(int x, int y, int width, int height) {
+        this.x = x;
+        this.y = y;
+        this.width = width;
+        this.height = height;
+        this.rect = new Rectangle(x, y, width, height);
+    }
+
+    @Override
+    public void paint(Graphics g) {
+        Color c = g.getColor();
+        g.setColor(Color.DARK_GRAY);
+        g.fillRect(x, y, width, height);
+        g.setColor(c);
+    }
+}