java - Java中int a[5],int a[],int a[]={2,3}的区别

Question

这个问题已经有答案了:

Array initialisation in java (5 个回答)

已关闭 6 年前。

我们如何静态声明数组？不可以是int a[5]; ？

package oops;

public class exception { 
    int arr1[] = new int[10];

    public static void main(String args[]){
        int a[] ={1,9};
        int[] a ;
        int a[9];
        a[0]=10;
    }
}

Answer 1

考虑以下场景

// Create new array with the following two values
int a[] = {1,9};
Assert.assertTrue( 2 == a.length );
Assert.assertTrue( 1 == a[0] );
Assert.assertTrue( 9 == a[1] );

// Create a new, uninitialized array
int[] a;
Assert.assertTrue( null == a );
Assert.assertTrue( 0 == a.length ); // NullPointerException

int a[9]; // this will not compile, should be
int a[] = new int[9];
Assert.assertTrue( 9 == a.length );
Assert.assertTrue( null == a[0] );

// Provided 'a' has not been previously defined
int a[];
a[0] = 10; // NullPointerExcpetion

// Provided 'a' has been defined as having 0 indicies
int a[] = new int[0];
a[0] = 10; // IndexOutOfBoundsException

// Provided 'a' has been defined as an empty array
int a[] = new int[1];
a[0] = 10; // Reassign index 0, to value 10.