使用System.arraycopy()实现数组之间的复制

System提供了一个静态方法arraycopy(),我们可以使用它来实现数组之间的复制。其函数原型是：

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

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．

有趣的是这个函数可以实现自己到自己复制，比如：

int[] fun ={0,1,2,3,4,5,6}; 

System.arraycopy(fun,0,fun,3,3);

则结果为：{0,1,2,0,1,2,6};

实现过程是这样的，先生成一个长度为length的临时数组,将fun数组中srcPos 

到srcPos+length-1之间的数据拷贝到临时数组中，再执行System.arraycopy(临时数组,0,fun,3,3).

评论

3 楼 hikaru1012 2010-10-09  

楼主解释的正确。只有在源数组和目的数组是同一个数组时才会创建临时数组。

2 楼 hikaru1012 2010-10-09  

java.lang.System.arraycopy注释


void java.lang.System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
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.)

パラメーター:
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.
スロー:
IndexOutOfBoundsException - if copying would cause access of data outside array bounds.
ArrayStoreException - if an element in the src array could not be stored into the dest array because of a type mismatch.
NullPointerException - if either src or dest is null.

1 楼 vivid_gxp 2009-09-13  

兄弟，你是怎么知道她的实现过程的？
据我所知，arraycopy是实现跨平台的。windows系统下是调用某个 dll 的。
而且arraycopy是通过native来声明的，那么就应该是通过C/C++来实现的。那你怎么就能肯定是用了一个临时数组呢？
如果需要将数据拷贝到临时数组，那么性能会很低的。
所以我觉得不应该像楼主所说的那样的。

（ps：(我也不知道具体是怎么实现的，上面的评论只是我的估计。）