methods - 空指针异常错误作为方法参数

Question

我使用两个 sprite 作为方法的参数，但出现空指针异常错误。 这是我的代码。 错误在 checkCollision 方法中。 我试图声明参数 Sprite s1 和 Sprite s2 但它们仍然无法识别。我不确定我做错了什么，因为当我将其他 Sprites 声明为参数时，没有空指针异常。我将衷心感谢您的帮助。提前谢谢你。

Sprite p;
Sprite e;
Sprite f;
Sprite q;
Sprite l;
Sprite m;
Sprite n;
PImage red_brick;
PImage other_block;
final static float MOVE_SPEED = 5;
final static float SPRITE_SCALE = 50.0/128;
final static float SPRITE_SIZE = 50.0;
final static float GRAVITY = 0.6;
ArrayList <Sprite> platforms;



void setup(){
 size(1000,600);
 createPlatforms("data/map.csv");
 red_brick = loadImage("block.png");
 other_block = loadImage("diamond.png");
 platforms = new ArrayList <Sprite>();
 platforms.add(e);
  platforms.add(f);
   platforms.add(q);
    platforms.add(l);
     platforms.add(m);
  platforms.add(n);
 imageMode(CENTER);
 
p = new Sprite("data/sprite.png", 0.5,67,450);



e = new Sprite("data/block.png", 1.0, 67, 600);
f = new Sprite("data/block.png", 1.0, 195, 600);
q = new Sprite("data/block.png", 1.0, 323, 600);
l = new Sprite("data/block.png", 1.0, 451, 600);
m = new Sprite("data/diamond.png", 1.0, 451, 472);
n = new Sprite("data/bigblock.png", 1.0, 907,600);

resolvePlatformCollisions(p, platforms);

}

void draw(){
  background(255);
p.display(); 
e.display();
f.display();
q.display();
l.display();
m.display();
n.display();
p.update();

}
boolean checkCollision(Sprite s1, Sprite s2){
  boolean noXOverlap = s1.getRight() <= s2.getLeft()|| s1.getLeft() >= s2.getRight(); Error 
  boolean noYOverlap = s1.getBottom() <= s2.getTop() || s1.getTop() >= s2.getBottom(); Error 
  if (noXOverlap || noYOverlap){
    return false;
  }
  else{
    return true;
  }
}



public void resolvePlatformCollisions(Sprite s, ArrayList <Sprite> walls){
  s.change_y += GRAVITY;
  s.center_y += s.change_y;
  ArrayList <Sprite > col_list = checkCollisionList(s, walls);
  if(col_list.size() > 0){
  Sprite collided = col_list.get(0);
  if(s.change_y > 0){
    s.setBottom(collided.getTop());
  }
  else if(s.change_y >0){
    s.setTop(collided.getBottom());
  }
  s.change_y = 0;
  }
   
  s.center_x += s.change_x;
 col_list = checkCollisionList(s, walls);
  if(col_list.size() > 0){
  Sprite collided = col_list.get(0);
  if(s.change_x > 0){
    s.setRight(collided.getLeft());
  }
  else if(s.change_x >0){
    s.setLeft(collided.getRight());
  }
  s.change_x = 0;
  }
}


public ArrayList <Sprite> checkCollisionList(Sprite s, ArrayList <Sprite> list){
  ArrayList <Sprite> collision_list = new ArrayList<Sprite>();
  for(Sprite p : list){
    if (checkCollision(s,p))
    collision_list.add(p);}
    return collision_list;
}


void keyPressed(){
  if(keyCode == RIGHT){
    p.change_x = 5;
  }
  else if(keyCode == LEFT){
    p.change_x = -5;
  }
  else if (keyCode == UP){
    p.change_y = -5;
}
    else if (keyCode == DOWN){
      p.change_y = 5;}
}

void keyReleased(){
  if(keyCode == RIGHT){
    p.change_x = 0;
  }
  else if(keyCode == LEFT){
    p.change_x = 0;
  }
  else if(keyCode == UP){
    p.change_y =0;
  }

    else if (keyCode == DOWN){
      p.change_y = 0;}
      
      
}

void createPlatforms(String filename){
  String[] lines = loadStrings(filename);
  for(int row = 0; row <lines.length; row++){
    String [] values = split(lines [row], ",");
    for(int col = 0; col< values.length; col++){
      if(values[col].equals("1")){
        Sprite s = new Sprite (red_brick, SPRITE_SCALE);
        s.center_x = SPRITE_SIZE/2 + col * SPRITE_SIZE;
         s.center_y = SPRITE_SIZE/2 + row * SPRITE_SIZE;
         
      }
   if (values[col].equals("2")){
     Sprite s = new Sprite (other_block, SPRITE_SCALE);
     s.center_x = SPRITE_SIZE/2 + col * SPRITE_SIZE;
     s.center_y = SPRITE_SIZE/2 + row * SPRITE_SIZE;
     
    }
  }
}
}

Answer 1

e, l, f, ... 是“空指针”。没有对象分配给此引用。在将它们附加到 ArrayList 之前，您需要创建 Sprite 对象:

void setup() {

    // [...]

    platforms = new ArrayList <Sprite>();

    e = new Sprite(... your parameters for sprite e ...);
    platforms.add(e);

    f = new Sprite(... your parameters for sprite f ...);
    platforms.add(f);

    // [...]