方法中的NullPointerException

Question

我有一个方法,返回一个类型SENSOR在粗体是我得到一个运行时NullPointerException,无法理解为什么.

 public Sensor getSensorAt(int x,int y,GridMap grid)
      {
       /*go through sensor storage array 
       * for eachsensor index call the get x get y method for that 
       * compare it to the x,y of the robot 
       * 
       */  

        for(int i=0;i<s1.length;i++){ 
             if(s1[i].getX() == x){    <======= NullpointerException
            if(s1[i].getY()== y){ 

            return s1[i]; 
            } 
          }      
        } 
        return null;
      }

Answer 1

你没有告诉我们在哪里s1创建,但看起来s1它没有任何东西用于某些索引i.

我倾向于编写我的for循环,以使这样的代码更清洁

Object result = null;
for(int i=0;i<s1.length;i++){ 
    Object current = s1[i]; // Replace Object with whatever your array actually contains
    if(current.getX() == x && current.getY() == y) {
        result = current;
        break; // if you only need the first match
    }
}

return result;

像格式化这样的东西很重要,它可以帮助你首先防止错误,并在发生错误时更容易找到错误....