Java对于每个循环对象分配均不起作用 [英] Java For each loop object assignment is not working

问题描述

 公共类A {int val;公开A {int val} {this.val = val;}公共无效print(){System.out.println(val);}公共静态void main(String args []){A [] aList =新的A [10];int temp = 1;for(A a:aList){a =新的A(temp ++);}for(A a:aList){打印();;}}} 

在A.main的线程"main"中获取异常java.lang.NullPointerException(A.java:28)aList地址空间A类对象已存储，但是再次迭代无法获取存储的对象，这些对象存储在哪里?

解决方案

a 是for循环的局部变量，因此分配给它不会影响aList数组的元素./p>

您应该使用常规的for循环来初始化数组:

  for(int i = 0; i< aList.length; i ++){aList [i] =新的A(temp ++);} 

public class A{

    int val;    
    public A(int val){
        this.val = val;
    }

    public void print() {
        System.out.println(val);

    }


    public static void main(String args[]){

        A[] aList = new A[10];
        int temp =1;

        for(A a : aList){
            a = new A(temp++);          
        }

        for(A a : aList){
            a.print();;         
        }

    }


}

Getting Exception in thread "main" java.lang.NullPointerException at A.main(A.java:28) aList address space Class A objects are stored but again iterate unable to get stored objects, where are the objects stored ?

解决方案

a is a local variable of the for loop, so assigning to it doesn't affect the elements of the aList array.

You should use a regular for loop to initialize the array :

    for(int i = 0; i < aList.length; i++){
        aList[i] = new A(temp++);          
    }

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