java中，數(shù)組的復(fù)制有以下三種方式：

1. 調(diào)用System.arraycopy（Arrays.copyOfRange可以當作第四種，但是底層調(diào)用的是System.arraycopy，所以，認為是同一種，下面是Arrays.copyOfRange的方法實現(xiàn)）

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public static <T,U> T[] copyOfRange(U[] original, int from, int to, Class<? extends T[]> newType) {int newLength = to - from;if (newLength < 0)throw new IllegalArgumentException(from + " > " + to);T[] copy = ((Object)newType == (Object)Object[].class)? (T[]) new Object[newLength]: (T[]) Array.newInstance(newType.getComponentType(), newLength);System.arraycopy(original, from, copy, 0,Math.min(original.length - from, newLength));return copy;}

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2. 調(diào)用clone方法

3.利用for循環(huán)自己實現(xiàn)

效率比較上，通過下面程序可以看出

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/*** */ package collection;import java.util.Arrays; import java.util.Date;/*** @author yfei* Date:2013-8-26*/ public class Array {public static final int size = 1000000;public static void copyByArrayCopy(String[] strArray){Long startTime = System.currentTimeMillis();String[] destArray = new String[size];System.arraycopy(strArray,0,destArray,0,strArray.length);//printArr(destArray);Long endTime = System.currentTimeMillis();System.out.println("copyByArrayCopy cost time is "+(endTime-startTime));}public static void copyByLoop(String[] strArray){Long startTime = System.currentTimeMillis();String[] destArray = new String[size];for(int i = 0;i<strArray.length;i++){destArray[i] = strArray[i];}//printArr(destArray);Long endTime = System.currentTimeMillis();System.out.println("copyByLoop cost time is "+(endTime-startTime));}public static void copyByClone(String[] strArray){Long startTime = System.currentTimeMillis();String[] destArray = strArray.clone();Long endTime = System.currentTimeMillis();System.out.println("copyByClone cost time is "+(endTime-startTime));}public static void main(String args[]){String arr1[] = new String[size];for(int i=0;i<size;i++){arr1[i] = "this is a test"+i;//arr1[i] = "shishangzhiyoumamahaoyouamdehaizixiangkuaibaotoujinmamadehuaibaoxingfuxiangbuliaoshishangzhiyoumamahaomeimadehaizixianggencaolikaimamadehuaibaoxingfunalizhaoshishangzhiyoumamahaomeimadehaizibuzhidaoyaoshitazhidaomengliyehuixiao"+i;}String arr2[] = new String[size];for(int i=0;i<size;i++){arr2[i] = "this is a test"+i;//arr2[i] = "shishangzhiyoumamahaoyouamdehaizixiangkuaibaotoujinmamadehuaibaoxingfuxiangbuliaoshishangzhiyoumamahaomeimadehaizixianggencaolikaimamadehuaibaoxingfunalizhaoshishangzhiyoumamahaomeimadehaizibuzhidaoyaoshitazhidaomengliyehuixiao"+i;}String arr3[] = new String[size];for(int i=0;i<size;i++){arr3[i] = "this is a test"+i;//arr3[i] = "shishangzhiyoumamahaoyouamdehaizixiangkuaibaotoujinmamadehuaibaoxingfuxiangbuliaoshishangzhiyoumamahaomeimadehaizixianggencaolikaimamadehuaibaoxingfunalizhaoshishangzhiyoumamahaomeimadehaizibuzhidaoyaoshitazhidaomengliyehuixiao"+i;}copyByClone(arr1);copyByLoop(arr2);copyByArrayCopy(arr3);}public static void printArr(String[] strArray){for(String str:strArray){System.out.println(str);}} }

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結(jié)果(ms單位)：

copyByClone cost time is 2
copyByLoop cost time is 352
copyByArrayCopy cost time is 3

由此可以看出，clone和arraycopy的效率基本是一致的，而通過循環(huán)copy的效率最慢。

看了一下源代碼：

clone：

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protected native Object clone() throws CloneNotSupportedException;

arraycopy

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

兩種方式都是用native ?method。

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簡單地講，一個Native Method就是一個java調(diào)用非java代碼的接口。一個Native Method是這樣一個java的方法：該方法的實現(xiàn)由非java語言實現(xiàn)，比如C。這個特征并非java所特有，很多其它的編程語言都有這一機制，比如在C＋＋中，你可以用extern "C"告知C＋＋編譯器去調(diào)用一個C的函數(shù)。

java的性能是不能言說的傷啊。。。

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轉(zhuǎn)載于:https://www.cnblogs.com/james1207/p/3283397.html

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