“线程中的异常”；AWT-EventQueue-0“；java.lang.NullPointerException[NetBeans]

我试图从代理类、障碍类和MovingEntity类调用draw（）方法，但我得到了以下错误：（我只有障碍类的错误）

world.java：

import java.util.*;
import java.awt.Color; 

public class World {

    int W,H;
    int margin;
    int N;

    LinkedList entities;

    public World() {
        W = 800;
        H = 600;
        margin = 50;

        entities = new LinkedList();

        N = 10;            
        for(int i=0; i<N; i++) {            
            Agent e = new Agent ( randomPointInsideWorld(), randomPointInsideWorld(), this );
            entities.add( e );
        }

        for(int i=0; i<4; i++) {            
            Obstacle o = new Obstacle ( randomPointInsideWorld(), this );
            entities.add( o );    
        }

        for(int i=0; i<3; i++) {            
            MovingEntity me = new MovingEntity ( randomPointInsideWorld(), this );
            entities.add( me );    
        }
    }

    int getW() { return W; }
    int getH() { return H; }

    Vec2D randomPointInsideWorld() {        
        double x = margin + Math.random() * (W - 2*margin);
        double y = margin + Math.random() * (H - 2*margin); 
        Vec2D p = new Vec2D(x,y);
        return p;
    }

    void processCollisions() {        
          for(int i=0; i<N; i++) {
              Entity ei = (Entity) entities.get(i);
              ei.setCollides(false);
          }

          for(int i=0; i<N; i++) {
              Entity ei = (Entity) entities.get(i);
              ei.setCollides(false);
              for(int j=0; j<N; j++) {  
                  if(i == j) continue;
                  Entity ej = (Entity) entities.get(j);
                  if(ei.collides(ej)) {
                      ei.setCollides(true);
                  }
              }
          }
    }

    void removeOutsiders() {
        for(int i=0; i<entities.size(); i++) {
            Entity ei = (Entity) entities.get(i);            
            if((ei.getPos().getX() < 0) ||
               (ei.getPos().getX() > W) ||
               (ei.getPos().getY() < 0) ||
               (ei.getPos().getY() > H))
            {
                entities.remove(ei);
            }
        }

        N = entities.size();
    }

    void update() {              
        removeOutsiders();
        processCollisions();

        for(int i=0; i<N; i++) {
            Entity ei = (Entity) entities.get(i);
            ei.update();

            if ( ei instanceof Agent ) {

                Agent a = (Agent) ei;
                if ( a.objReached() ) {
                    a.setObj(randomPointInsideWorld() );
                }
            }
        }
    }

    public void run(int steps) {
        for(int i = 0; i<steps; i++) update();
    }

    public void draw( java.awt.Graphics g ) {
        N = entities.size(); 
        for(int i=0; i<N; i++) {
            Entity ei = (Entity) entities.get(i);
            Vec2D p = ei.getPos();
            double wa = 2;
            g.setColor(Color.BLUE);    
            g.fillOval((int)(p.getX() - wa), (int)(p.getY() - wa), 2*(int)wa, 2*(int)wa);
            if ( ei instanceof Agent ) {
                Agent a = (Agent) ei;
                a.draw(g);
            }
            if ( ei instanceof MovingEntity ) {
                MovingEntity me = (MovingEntity) ei;
                me.draw(g);
            }
            if ( ei instanceof Obstacle ) {
                Obstacle obst = (Obstacle) ei;
                obst.draw(g);
            }
        }
    }
}

我是Java的新手，但我有一种感觉，这与障碍类中的某些值没有正确初始化有关。。。会吗

---

谢谢大家。

private myp未在
障碍中初始化。java

改变

 public Obstacle (Vec2D p, World wi) {
      super (p, wi);  
      MyPolygon p1 = new MyPolygon();
      p1.randomPolygon();
      p1.center();
      p1.translate((int)pos.getX(), (int)pos.getY());
  }

到

将此更改为

private MyPolygon p = new MyPolygon();

指向异常中引用的确切行。=）从birder.draw（birder.java:28）

开始。可能的问题是

p

为空。已解决！非常感谢：D

 public Obstacle (Vec2D p, World wi) {
      super (p, wi);  
      MyPolygon p1 = new MyPolygon();
      p1.randomPolygon();
      p1.center();
      p1.translate((int)pos.getX(), (int)pos.getY());
  }

 public Obstacle (Vec2D v, World wi) {
      super (v, wi);  
      p = new MyPolygon();
      p.randomPolygon();
      p.center();
      p.translate((int)pos.getX(), (int)pos.getY());
  }

private MyPolygon p = new MyPolygon();