System.arraycopy()使用小记

我们在编程实践中经常会需要进行数组的复制,不但要复制数组的基本结构,还要复制其中的数据,遇到这种情况该怎么处理呢?不用愁,java给我们提供了一个System.arraycopy() 方法来解决这个问题。

函数原型:

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

函数说明:
arraycopy()是System类提供的一个静态方法,可以用它来实现数组之间的复制。

参数说明:
src:源数组;
srcPos:源数组要复制的起始位置;
dest:目的数组;
destPos:目的数组放置的起始位置;
length:复制的长度。

注意:
src and dest都必须是同类型或者可以进行转换类型的数组。

示例:

public class ArrayTest {
public static void main(String[] args) {
String[] str1 = {“aaa”,”bbb”,”ccc”};
String[] str2 = {“ddd”,”eee”,”fff”};
String[] str3 = new String[6];
System.arraycopy(str1, 0, str3, 0, 3);
System.arraycopy(str2, 0, str3, 3, 3);
for (int i = 0; i < str3.length; i++) { System.out.println(str3[i]); } } }

JDK1.5API文档中对arraycopy函数的说明:
Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. A subsequence of array components are copied from the source array referenced by src to the destination array referenced by dest. The number of components copied is equal to the length argument. The components at positions srcPos through srcPos+length-1 in the source array are copied into positions destPos through destPos+length-1, respectively, of the destination array.
If the src and dest arguments refer to the same array object, then the copying is performed as if the components at positions srcPos through srcPos+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positions destPos through destPos+length-1 of the destination array.

If dest is null, then a NullPointerException is thrown.

If src is null, then a NullPointerException is thrown and the destination array is not modified.

Otherwise, if any of the following is true, an ArrayStoreException is thrown and the destination is not modified:

The src argument refers to an object that is not an array.
The dest argument refers to an object that is not an array.
The src argument and dest argument refer to arrays whose component types are different primitive types.
The src argument refers to an array with a primitive component type and the dest argument refers to an array with a reference component type.
The src argument refers to an array with a reference component type and the dest argument refers to an array with a primitive component type.
Otherwise, if any of the following is true, an IndexOutOfBoundsException is thrown and the destination is not modified:

The srcPos argument is negative.
The destPos argument is negative.
The length argument is negative.
srcPos+length is greater than src.length, the length of the source array.
destPos+length is greater than dest.length, the length of the destination array.
Otherwise, if any actual component of the source array from position srcPos through srcPos+length-1 cannot be converted to the component type of the destination array by assignment conversion, an ArrayStoreException is thrown. In this case, let k be the smallest nonnegative integer less than length such that src[srcPos+k] cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions srcPos through srcPos+k-1 will already have been copied to destination array positions destPos through destPos+k-1 and no other positions of the destination array will have been modified. (Because of the restrictions already itemized, this paragraph effectively applies only to the situation where both arrays have component types that are reference types.)

Parameters:
src – the source array.
srcPos – starting position in the source array.
dest – the destination array.
destPos – starting position in the destination data.
length – the number of array elements to be copied.

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