Java System.arraycopy()是一种本地静态方法，用于将元素从源数组复制到目标数组。

System.arraycopy()方法参数

System.arraycopy()方法签名为：

public static native void arraycopy(Object src,  int  srcPos,
   Object dest, int destPos,
   int length);

• src：源数组。

• srcPos：从中开始复制的源数组索引

• dest：目标数组。

• destPos：从中复制数据的目标数组索引。

• 长度：要复制的元素数。

Java System.arraycopy()示例

让我们看一个使用此方法复制数组的简单示例。

package com.theitroad.examples;

import java.util.Arrays;

public class SystemArrayCopy {

	public static void main(String[] args) {
		int[] source = { 1, 2, 3, 4, 5, 6, 7 };
		int[] destination = new int[5];

		System.arraycopy(source, 3, destination, 2, 3);

		System.out.println(Arrays.toString(destination));
	}
}

Java System.arraycopy()示例

要复制的源数组中的元素为4,5,6。
它们将从索引2开始复制到目标数组。

当源和目标是同一数组时，System.arraycopy()

当源和目标是相同的阵列时，将从源阵列创建一个临时阵列。
然后将临时数组中的元素复制到源数组。

jshell> int[] source = { 1, 2, 3, 4, 5, 6, 7 };
source ==> int[7] { 1, 2, 3, 4, 5, 6, 7 }

jshell> System.arraycopy(source, 3, source, 5, 2);

jshell> System.out.println(Arrays.toString(source));
[1, 2, 3, 4, 5, 4, 5]

系统arraycopy()方法的异常情况

arraycopy()方法有5个参数。
因此，在许多情况下会发生异常。
此方法引发的异常是：

• NullPointerException：如果源或者目标数组为null。

• ArrayStoreException：如果源和目标数组类型不匹配或者不是数组。

• ArrayIndexOutOfBoundsException：如果由于索引值导致数据溢出或者它们为负数。

让我们看一下这些异常情况的一些示例。

1. NullPointerException示例

jshell> System.arraycopy(source, 3, null, 2, 3);
|  Exception java.lang.NullPointerException
|        at System.arraycopy (Native Method)
|        at (#4:1)

jshell> System.arraycopy(null, 3, source, 2, 3);
|  Exception java.lang.NullPointerException
|        at System.arraycopy (Native Method)
|        at (#5:1)

2.当源和目标不是数组时，ArrayStoreException

jshell> System.arraycopy(new Object(), 3, source, 2, 3);
|  Exception java.lang.ArrayStoreException: arraycopy: source type java.lang.Object is not an array
|        at System.arraycopy (Native Method)
|        at (#6:1)

jshell> System.arraycopy(source, 3, "ABC", 2, 3);
|  Exception java.lang.ArrayStoreException: arraycopy: destination type java.lang.String is not an array
|        at System.arraycopy (Native Method)
|        at (#7:1)

3.当源和目标数组不兼容时，ArrayStoreException

jshell> int[] source = {1, 2, 3}
source ==> int[3] { 1, 2, 3 }

jshell> String[] destination = new String[5];
destination ==> String[5] { null, null, null, null, null }

jshell> System.arraycopy(source, 0, destination, 0, 2);
|  Exception java.lang.ArrayStoreException: arraycopy: type mismatch: can not copy int[] into object array[]
|        at System.arraycopy (Native Method)
|        at (#10:1)

4.索引或者长度为负数时，ArrayIndexOutOfBoundsException

jshell> int[] source = {1, 2, 3}
source ==> int[3] { 1, 2, 3 }

jshell> int[] dest = new int[5];
dest ==> int[5] { 0, 0, 0, 0, 0 }

jshell> System.arraycopy(source, -1, dest, 0, 2);
|  Exception java.lang.ArrayIndexOutOfBoundsException: arraycopy: source index -1 out of bounds for int[3]
|        at System.arraycopy (Native Method)
|        at (#15:1)

jshell> System.arraycopy(source, 1, dest, -1, 2);
|  Exception java.lang.ArrayIndexOutOfBoundsException: arraycopy: destination index -1 out of bounds for int[5]
|        at System.arraycopy (Native Method)
|        at (#16:1)

jshell> System.arraycopy(source, 1, dest, 0, -2);
|  Exception java.lang.ArrayIndexOutOfBoundsException: arraycopy: length -2 is negative
|        at System.arraycopy (Native Method)
|        at (#17:1)

5. srcPos + length大于src.length时，ArrayIndexOutOfBoundsException

jshell> System.arraycopy(source, 0, dest, 0, 4);
|  Exception java.lang.ArrayIndexOutOfBoundsException: arraycopy: last source index 4 out of bounds for int[3]
|        at System.arraycopy (Native Method)
|        at (#18:1)

6.当destPos + length大于dest.length时，ArrayIndexOutOfBoundsException

jshell> int[] src = {1, 2, 3, 4}
src ==> int[4] { 1, 2, 3, 4 }

jshell> int[] dest = new int[2]
dest ==> int[2] { 0, 0 }

jshell> System.arraycopy(src, 0, dest, 0, 3);
|  Exception java.lang.ArrayIndexOutOfBoundsException: arraycopy: last destination index 3 out of bounds for int[2]
|        at System.arraycopy (Native Method)
|        at (#21:1)