41 Java语言基础数组操作的两个常见小问题越界和空指针

1 class Demo3_Array{
2     public static void main(String[] args) {
3             int[] arr = {1,2,3};
4             System.out.println(arr[4]);  //Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
5 
6     }
7 }

 1 class Demo3_Array{
 2     public static void main(String[] args) {
 3             int[] arr = {1,2,3};
 4             System.out.println(arr[4]);  //Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
 5             
 6 
 7             arr = null;
 8             System.out.println(arr[0]);//Exception in thread "main" java.lang.NullPointerException
 9     }
10 }