出现NullPointerException，到底错在哪里？

niexinnm

本学期刚开了JAVA，之前没接触过OO，很是头痛阿……
这程序是想产生一个随机数组，并有方法显示其平均值，但在在public void initializeArray()这里出现NullPointerException，是哪里不对呢？

public class RandomArray { &nbsp;&nbsp;&nbsp;&nbsp;int length; &nbsp;&nbsp;&nbsp;&nbsp;double randomArray[]; &nbsp;&nbsp;&nbsp;&nbsp;public RandomArray() { &nbsp;&nbsp;&nbsp;&nbsp;double randomArray[] = new double[0]; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;public RandomArray(int length) { &nbsp;&nbsp;&nbsp;&nbsp;this.length = length; &nbsp;&nbsp;&nbsp;&nbsp;double randomArray[] = new double[length]; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;public void initializeArray() { &nbsp;&nbsp;&nbsp;&nbsp;for (int i = 0; i < randomArray.length; i++) { &nbsp;&nbsp;&nbsp;&nbsp;    randomArray[i] = Math.random() * 10; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;public double arrayAverage() { &nbsp;&nbsp;&nbsp;&nbsp;double sum = 0.0; &nbsp;&nbsp;&nbsp;&nbsp;double average = 0.0; &nbsp;&nbsp;&nbsp;&nbsp;for (int i = 0; i < length; i++) { &nbsp;&nbsp;&nbsp;&nbsp;    sum += randomArray[i]; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;average = sum / length; &nbsp;&nbsp;&nbsp;&nbsp;return average; &nbsp;&nbsp;&nbsp;&nbsp;} }

public class RandomArrayDemo {     public static void main(String[] args) {     RandomArray a = new RandomArray(10);     a.initializeArray();     System.out.println("The average of the array is: " +         a.arrayAverage());     } }

caojiqun

比较一下：

1. 
   
2. ........
   
3.     double randomArray[];
   
4. 
   
5.     public RandomArray() {
   
6.     double randomArray[] = new double[0];
   
7.     }
   
8. 
   
9.     public RandomArray(int length) {
   
10.     this.length = length;
    
11.     double randomArray[] = new double[length];
    
12.     }
    
13. ........
    

复制代码

1. 
   
2. ........
   
3.     double[] randomArray;
   
4. 
   
5.     public RandomArray() {
   
6.            randomArray = new double[0];
   
7.     }
   
8. 
   
9.     public RandomArray(int length) {
   
10.          this.length = length;
    
11.          randomArray = new double[length];
    
12.     }
    
13. ........
    

复制代码

niexinnm

明白了，多谢大侠相助^_^