新手求指点，坦克大战的问题

Kamoe 2013-04-04 10:58:14

//这个是Tank类里的一个方法
public Bullet fire() {
int x = this.x + MyTank.WIDTH/2 - Bullet.WIDTH/2;
int y = this.y + MyTank.HEIGH/2 - Bullet.HEIGH/2;
Bullet bullet = new Bullet(x, y, barrelDir, tc);
tc.bullets.add(bullet);//运行的时候出现空指针错误，说是这里，好像是没添加进去，用DeBug查的时候也是在这里就跳进了一个很多很长的代码里，不知道为什么会出现这种错误，求解，如果代码不详细我还会再贴，谢谢了
return bullet;
}

我在TankClient类里有

List<Bullet> bullets = new ArrayList<Bullet>();
....
public void paint(Graphics g) {
myTank.draw(g);

for(int i=0; i<bullets.size(); i++) {
bullets.get(i).draw(g);
}
}

...全文

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我自横刀香甜笑 2013-04-04

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tc是什么？初始化了吗？

a_a\\\ 2013-04-04

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tc应该没有new吧！空指针的异常，一般都是因为某些对象没有实例化。建议你认真检查一下对象有没有实例化或赋值

a_a\\\ 2013-04-04

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引用 9 楼 inuyashazh 的回复:

package tankwar; import java.awt.Color; import java.awt.Graphics; import java.awt.Image; import java.awt.Toolkit; import java.awt.event.KeyEvent; public class MyTank { int ……

你没有new， TankClient tc = new TankClient();

a_a\\\ 2013-04-04

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package tankwar;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;



public class MyTank {

int x;
int y;
public static final int WIDTH = 30;
public static final int HEITHT = 30;
int X_SPEED = 5;
int Y_SPEED = 5;

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

private boolean isLeft = false;
private boolean isUp = false;
private boolean isRight = false;
private boolean isDown = false;
enum Direction {
L, LU, U, RU, R, RD, D, LD, STOP
};

public TankClient tc = null;        //这里写null了，请检查

public Direction dir = Direction.L;
Direction barrelDir = dir;

public void draw(Graphics g) {
Color c = g.getColor();
g.setColor(Color.green);
g.fillOval(this.x, this.y, WIDTH, HEITHT);
g.setColor(c);
barrelDraw(g);
move();
}

public void barrelDraw(Graphics g) {
Color c = g.getColor();
g.setColor(Color.BLACK);
switch (barrelDir) {
case L:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y + WIDTH/2);
break;
case LU:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y);
break;
case U:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH/2, this.y);
break;
case RU:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y);
break;
case R:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y + HEITHT/2);
break;
case RD:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y + HEITHT);
break;
case D:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH/2, this.y + HEITHT);
break;
case LD:
g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y + HEITHT);
break;
case STOP:
break;
}
}

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

if(this.dir != Direction.STOP) {
this.barrelDir = this.dir;
}

if(isLeft == true && isUp == false && isRight == false && isDown == false) dir = Direction.L;
if(isLeft == false && isUp == true && isRight == false && isDown == false) dir = Direction.U;
if(isLeft == false && isUp == false && isRight == true && isDown == false) dir = Direction.R;
if(isLeft == false && isUp == false && isRight == false && isDown == true) dir = Direction.D;

if(isLeft == true && isUp == true && isRight == false && isDown == false) dir = Direction.LU;
if(isLeft == false && isUp == true && isRight == true && isDown == false) dir = Direction.RU;
if(isLeft == false && isUp == false && isRight == true && isDown == true) dir = Direction.RD;
if(isLeft == true && isUp == false && isRight == false && isDown == true) dir = Direction.LD;
if(isLeft == false && isUp == false && isRight == false && isDown == false) dir = Direction.STOP;
}

public Bullet fire() {
int x = this.x + MyTank.WIDTH/2 - Bullet.WIDTH/2;
int y = this.y + MyTank.HEITHT/2 - Bullet.HEIGHT/2;
Bullet bullet = new Bullet(x, y, barrelDir);
tc.bullets.add(bullet);
return bullet;
}

public void KeyPressed(KeyEvent e) {
int key = e.getKeyCode();
switch (key) {
case KeyEvent.VK_LEFT:
isLeft = true;
break;
case KeyEvent.VK_UP:
isUp = true;
break;
case KeyEvent.VK_RIGHT:
isRight = true;
break;
case KeyEvent.VK_DOWN:
isDown = true;
break;
}

}

public void KeyReleased(KeyEvent e) {
int key = e.getKeyCode();
switch (key) {
case KeyEvent.VK_LEFT:
isLeft = false;
break;
case KeyEvent.VK_UP:
isUp = false;
break;
case KeyEvent.VK_RIGHT:
isRight = false;
break;
case KeyEvent.VK_DOWN:
isDown = false;
break;
case KeyEvent.VK_SPACE:
fire();
}
}

}

Kamoe 2013-04-04

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package tankwar; import java.awt.Color; import java.awt.Graphics; import java.awt.Image; import java.awt.Toolkit; import java.awt.event.KeyEvent; public class MyTank { int x; int y; public static final int WIDTH = 30; public static final int HEITHT = 30; int X_SPEED = 5; int Y_SPEED = 5; public MyTank(int x, int y, Direction dir) { this.x = x; this.y = y; this.dir = dir; } private boolean isLeft = false; private boolean isUp = false; private boolean isRight = false; private boolean isDown = false; enum Direction { L, LU, U, RU, R, RD, D, LD, STOP }; public TankClient tc = null; public Direction dir = Direction.L; Direction barrelDir = dir; public void draw(Graphics g) { Color c = g.getColor(); g.setColor(Color.green); g.fillOval(this.x, this.y, WIDTH, HEITHT); g.setColor(c); barrelDraw(g); move(); } public void barrelDraw(Graphics g) { Color c = g.getColor(); g.setColor(Color.BLACK); switch (barrelDir) { case L: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y + WIDTH/2); break; case LU: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y); break; case U: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH/2, this.y); break; case RU: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y); break; case R: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y + HEITHT/2); break; case RD: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH, this.y + HEITHT); break; case D: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x + WIDTH/2, this.y + HEITHT); break; case LD: g.drawLine(this.x + WIDTH/2, this.y + HEITHT/2, this.x, this.y + HEITHT); break; case STOP: break; } } public void move() { switch (dir) { case L: x = x - X_SPEED; break; case LU: x = x - X_SPEED; y = y - Y_SPEED; break; case U: y = y - Y_SPEED; break; case RU: x = x + X_SPEED; y = y - Y_SPEED; break; case R: x = x + X_SPEED; break; case RD: x = x + X_SPEED; y = y + Y_SPEED; break; case D: y = y + Y_SPEED; break; case LD: x = x - X_SPEED; y = y + Y_SPEED; break; case STOP: break; } if(this.dir != Direction.STOP) { this.barrelDir = this.dir; } if(isLeft == true && isUp == false && isRight == false && isDown == false) dir = Direction.L; if(isLeft == false && isUp == true && isRight == false && isDown == false) dir = Direction.U; if(isLeft == false && isUp == false && isRight == true && isDown == false) dir = Direction.R; if(isLeft == false && isUp == false && isRight == false && isDown == true) dir = Direction.D; if(isLeft == true && isUp == true && isRight == false && isDown == false) dir = Direction.LU; if(isLeft == false && isUp == true && isRight == true && isDown == false) dir = Direction.RU; if(isLeft == false && isUp == false && isRight == true && isDown == true) dir = Direction.RD; if(isLeft == true && isUp == false && isRight == false && isDown == true) dir = Direction.LD; if(isLeft == false && isUp == false && isRight == false && isDown == false) dir = Direction.STOP; } public Bullet fire() { int x = this.x + MyTank.WIDTH/2 - Bullet.WIDTH/2; int y = this.y + MyTank.HEITHT/2 - Bullet.HEIGHT/2; Bullet bullet = new Bullet(x, y, barrelDir); tc.bullets.add(bullet); return bullet; } public void KeyPressed(KeyEvent e) { int key = e.getKeyCode(); switch (key) { case KeyEvent.VK_LEFT: isLeft = true; break; case KeyEvent.VK_UP: isUp = true; break; case KeyEvent.VK_RIGHT: isRight = true; break; case KeyEvent.VK_DOWN: isDown = true; break; } } public void KeyReleased(KeyEvent e) { int key = e.getKeyCode(); switch (key) { case KeyEvent.VK_LEFT: isLeft = false; break; case KeyEvent.VK_UP: isUp = false; break; case KeyEvent.VK_RIGHT: isRight = false; break; case KeyEvent.VK_DOWN: isDown = false; break; case KeyEvent.VK_SPACE: fire(); } } } 这是tank类里的全部代码

Kamoe 2013-04-04