Java 中的空指针异常和范围

我正在尝试在 Java 环境中学习面向对象编程。我正在编写一个相当简单的代码，但收到此错误：

Exception in thread "main" java.lang.NullPointerException
at Advisor_score.Rating.Score(Rating.java:12)
at Advisor_score.Rating.main(Rating.java:25)

这是我的代码：

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

    public void print(){
        System.out.println(advisor_score);
    }

    public static void main(String[] args){ 
        double p1_1[] = {101,1,1,1.5,.5};
        Rating d = new Rating(p1_1);
        d.Score();
        d.print();
    }
}

我已经看了几个小时了，无法找出代码的问题。我是编程新手，有人可以帮助我吗？提前致谢！

public Rating (double [] x){
    double [] Ratings = x;
}

这里你声明一个局部变量Ratings并分配x到它。之后，变量就超出了范围。

你想做的是Ratings = x;，这将设置实例变量Ratings to x而不是创建一个新的且未使用的局部变量。