java - boolean 键[]获取NPE(空指针表达式)java不知道如何在游戏开始时分配它？

Question

这是主类，它扩展了另一个包含 gameloop() 的类。
keys() 在 gameloop() 内检查

private boolean keys[] ;
public void keyPressed(KeyEvent ke){
    keys[ke.getKeyCode()] = true;
}

void keys(){

    if(keys[KeyEvent.VK_Q] == true){ //NPE here (Null Pointer Expression)
        stop();
    } 

    if(keys[KeyEvent.VK_SPACE] == true && jump== false){
        jump = true;
        cjump = true;
        jkptime = System.currentTimeMillis();
        _7zl2m.setVY(-0.4f);
    } 

    if(_7zl2m.getX() >= (bg.getWidth(null) - _7zl2m.getWidth()) && keys[KeyEvent.VK_RIGHT] == true || _7zl2m.getX() <= _7zl2m.getWidth() + 15 && keys[KeyEvent.VK_LEFT] == true || _7zl2m.getY() <= bg.getHeight(null) - 350 && keys[KeyEvent.VK_UP] == true || _7zl2m.getY() >= bg.getHeight(null) - 160 && keys[KeyEvent.VK_DOWN] == true){
        if(keys[KeyEvent.VK_RIGHT] == true || keys[KeyEvent.VK_LEFT] == true){
            _7zl2m.setVX(0.0f);
        }else if(keys[KeyEvent.VK_UP] == true || keys[KeyEvent.VK_DOWN] == true){
            _7zl2m.setVY(0.0f);
        }
    }else{
        if(keys[KeyEvent.VK_RIGHT] == true && jump == false){
            _7zl2m.setVX(0.2f);
        }

        else if(keys[KeyEvent.VK_LEFT] == true && jump == false){
            _7zl2m.setVX(-0.2f);
        }

        if(keys[KeyEvent.VK_UP] == true && jump == false){
            _7zl2m.setVY(-0.2f);
        }

        else if(keys[KeyEvent.VK_DOWN] == true && jump == false){
            _7zl2m.setVY(0.2f);
        }
    }

    if(keys[KeyEvent.VK_RIGHT] == false || keys[KeyEvent.VK_LEFT] == false){    
        _7zl2m.setVX(0.00f);
    }else if (keys[KeyEvent.VK_UP] == false || keys[KeyEvent.VK_DOWN] == false ){
        _7zl2m.setVY(0.0f);
    }
}

//release a key
public void keyReleased(KeyEvent ke){
    keys[ke.getKeyCode()] = false;
}

当然它会是空的，因为我还没有按任何键......但是如何解决这个问题。 我已经尝试过尝试 block

Answer 1

您最好使用HashSet<Integer>在这里，因为您不知道所有按键都会被按下

像这样初始化

private Set<Integer> keys = new HashSet<Integer>() ;

向其添加值，例如

keys.add(someValue);

并检查

keys.contains(someValue);

发布时将其从 Set 中删除

keys.remove(someValue);