Java中面向对象编程的问题

Question

所以我想首先告诉你我正在自学Java,你们是我最接近老师的事情.非常感谢你提出我简单明了的问题.我只是想学习.我再次得到一个错误,对于我的生活,我无法弄明白.

这是错误:

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)

这是我的评级类的代码:

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;
}

这是我的其他类的代码:

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();
        }

    }

再一次,我在StackOverflow上不能感谢你们.你的帮助非常宝贵!

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.当你申报时

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

在某些时候,需要分配它

ADVISOR_SCORE = new double[size];