Question

我有一个计算特定成员所覆盖的总距离的方法，它返回一个双数组，如下所示：

public double[] getTotalDistances(){
  double[] distance;
   distance = new double[3];


    for(Activity r: diary ){

        if(r instanceof Run){
           distance[0] += r.getDistance(); 
        }


      }
    for(Activity c: diary ){
        if(c instanceof Cycle){
           distance[1] += c.getDistance(); 
        }
    }

    for(Activity s: diary ){
        if(s instanceof Swim){
           distance[2] += s.getDistance(); 
        }
    }


    return distance;
}

现在对象（成员）存储在另一个名为members的数组中，如下所示：

 public boolean addMember(Member m){
    boolean result = false;
        for(int i = 0; i < members.length; i++){
            if(members[i] == null){


                members[i] = m;
                result = true;
                break;
            }
        }


    return result; //this is returned to have an indication if the member was added successfully or not
}

现在我需要一种方法来打印成员的所有总距离，我试过这个：

public void displayDistances() {



        for(int i = 0; i < members[i].getTotalDistances().length; i++){
            System.out.println(members[i].getTotalDistances()[i]);
        }

}

但是，这只会打印第一个成员的第一个元素，然后是0，并在其上面给出一个空指针异常。任何帮助都会非常感激！

Answer 1

这里有几件事。首先，我重构了你的getTotalDistances（）方法。

public double[] getTotalDistances(){
   double[] distance = new double[3];

   for(Activity activity: diary) {
      if (activity instanceof Run) {
         distance[0] += activity.getDistance(); 
      } else if (activity instanceof Cycle) {
         distance[1] += activity.getDistance();
      } else {
         distance[2] += activity.getDistance();
      }
   }
   return distance;
}

然后你的displayDistances（）应改为：

public void displayDistances(){
   for(int i = 0; i < members.length; i++){
      double total = 0;
      double[] distances = members[i].getTotalDistances();
      for(int j = 0; j < ditances.length; j++){  
         total += distances[j];
      }
      System.out.println(total);
   }
}

这将打印每个成员的总行进距离。祝你好运！

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