1. Simple Code Examples

System.arraycopy()

int[] arr = {1,2,3,4,5}; int[] copied = new int[10];System.arraycopy(arr, 0, copied, 1, 5);//5 is the length to copy System.out.println(Arrays.toString(copied));

Output:

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0][0, 1, 2, 3, 4, 5, 0, 0, 0, 0]

Arrays.copyOf()

int[] copied = Arrays.copyOf(arr, 10); //10 the the length of the new arraySystem.out.println(Arrays.toString(copied)); copied = Arrays.copyOf(arr, 3);System.out.println(Arrays.toString(copied));

Output:

[1, 2, 3, 4, 5, 0, 0, 0, 0, 0][1, 2, 3]

2. The Major Difference

The difference is that Arrays.copyOf does not only copy elements, it also creates a new array.System.arrayCopy copies into an existing array.

If we read the source code of , we can see that it uses System.arraycopy().

public static int[] copyOf(int[] original, int newLength) {    int[] copy = new int[newLength];    System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));    return copy; }

总结：

1.copyOf()的实现是用的是arrayCopy();

2.arrayCopy()需要目标数组，对两个数组的内容进行可能不完全的合并操作。

3.copyOf()在内部新建一个数组，调用arrayCopy()将original内容复制到copy中去，并且长度为newLength。返回copy;