java - Java中面向对象编程的问题

Question

所以我想首先告诉您我正在自学 Java，你们是我最接近老师的人。非常感谢你容忍我这个简单而明显的问题。我只是想学习。我又一次遇到了一个我一生都无法弄清楚的错误。

这里是错误:

Exception in thread "main" java.lang.NullPointerException
at Advisor_score.All_user.Score1(All_user.java:13)
at Advisor_score.All_user.main(All_user.java:28)

这是我的评级类代码:

package Advisor_score;
public class Rating {
    double [] Ratings;
    double sum=0;
    double raw_advisor;
    double advisor_score;
public Rating (double [] x){
        Ratings = x;
        }

public double Score(){
for(int i=2;i<Ratings.length;i++){
    sum+=Ratings[i];
}
raw_advisor=((sum-(3*(Ratings.length-2)))/4);
advisor_score= 2.5+(2.5*(1-Math.pow(Math.E, -.5*raw_advisor)));
return advisor_score;
}

这是我的另一个类的代码:

package Advisor_score;      

public class All_user{
        double [] ADVISOR_SCORE;
        Rating [] All_users;
        double score;
        public All_user(Rating...args){
                All_users=args;
            }

        public double [] Score1(){
            for (int j = 0;j<All_users.length;j++){
                score=All_users[j].Score();
                ADVISOR_SCORE[j]=score;
                }
            return ADVISOR_SCORE;
        }
        public void print(){
            for(int i = 0;i<ADVISOR_SCORE.length;i++){
            System.out.println(ADVISOR_SCORE[i]);
            }
        }
        public static void main(String[] args){ 
            double p1_1[] = {101,1,5,5,5};
            double p2_1[] = {101,1,1,2,3};
            Rating d = new Rating(p1_1);
            Rating e = new Rating(p2_1);
            All_user all=new All_user(d, e);
            all.Score1();
            all.print();
        }

    }

再次感谢 StackOverflow 的各位。您的帮助非常宝贵!!

Answer 1

您尚未初始化 ADVISOR_SCORE 和 All_users 数组，但您确实尝试分配值并使用它们。当你声明

double[] ADVISOR_SCORE; // this is null until assigned

在某些时候，它需要被赋值

ADVISOR_SCORE = new double[size];