Java数组拷贝/复制的效率比较

今天在研究Jlibrtp代码时,偶然注意到里面大量使用了System.arraycopy()这个方法,心想既然是协议实现,那用的方法肯定都是效率最高或较高的了,以前对这个System.arraycopy()仅有个抽象的认识。另外,JDK中对ArrayListaddremove方法的实现,居然也是用的System.arraycopy(),让我不由得对其产生“敬意啊”。今天就来动手试一下到底谁的效率高,到底有多高。

C程序员们经常讨论数组复制的效率,此类笔试面试题也层出不穷。在Java中,数组拷贝可以用:1for循环;2clone方法;3System.arraycopy()。测试如下:

1)使用了一个70元素的字符串数组;

2)每种方法各循环拷贝N次。

统计结果如下:

 

重复1000

10

100

500

for循环

0

47

484

2421

clone方法

0

32

250

1235

System.arraycopy

0

16

94

437

很明显了,for循环最慢,约为clone方法的2倍,约为System.arraycopy4~5倍;System.arraycopy最快。

    PSSystem.arraycopy是调用的JNI,怪不得。

 

附测试代码:

package copytest;

public class ArrayCopyTest
{
    private static String [] src 
    = {"Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff",
        "Aaaaaaaaaa", "Vvvvvvv", "Bbbb", "Cccc", "Dddd", "Eddeee", "FFFFFFffffffff"};
    
    private static String [] dst;

    /**
     * @param args
     */
    public static void main(String[] args)
    {
        // TODO Auto-generated method stub
        System.out.println(forCopy(5000000));
        System.out.println(cloneCopy(5000000));
        System.out.println(systemJNICopy(5000000));
    }
    
    /**
     * 使用for来复制数组
     * @param time 循环执行的次数
     * @return 执行的总时间
     */
    public static long forCopy(int time)
    {
        long start = System.currentTimeMillis();
        while(time-- > 0)
        {
            int size = src.length;
            dst = new String [size];
            for (int i = 0; i < size; i++)
            {
                dst[i] = src[i];
            }
        }
        long end = System.currentTimeMillis();
        return (end - start);
    }
    
    public static long cloneCopy(int time)
    {
        long start = System.currentTimeMillis();
        while(time-- > 0)
        {
            dst = (String[])src.clone();
        }
        long end = System.currentTimeMillis();
        return (end - start);
    }
    
    public static long systemJNICopy(int time)
    {
        long start = System.currentTimeMillis();
        while(time-- > 0)
        {
            int size = src.length;
            System.arraycopy(src, 0, dst, 0, size);
        }
        long end = System.currentTimeMillis();
        return (end - start);
    }

}
 

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