五千年(敝帚自珍)

主题：【倡议】Java SE 5.0和.NET 2.0擂台赛 -- Highway

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复 【倡议】Java SE 5.0和.NET 2.0擂台赛
家园 String, StringBuffer &StringBuilder的玄妙

String可能是使用最广泛的一种操作了，尤其是在现在Web程序开发中。事实上，Java的String是非常特殊的一种Class，即所有的String Object都是Immutable的。为什么要这样对待String呢？因为Sun想尽可能的榨取一切可能的性能。

为了提高连续拼接String的性能，Java提供了一个类叫StringBuffer。使用它在某些情况下可以成千倍的提高性能。但是Sun还是不够满意，在Java 5.0中，它又提供了一个类叫做StringBuilder。

那么StringBuilder和StringBuffer有什么区别呢？StringBuffer是Thread-safe的，而StringBuilder不是。

那么什么是Thread-safe呢？还记得国内火车内的那种厕所吗？一个人进去，把门一锁，然后开始“方便”。其间不会被外人打扰。完事后开门出来，下一个人才能进去。不会有两个人同时一起“方便”的尴尬局面。这就是Thread-safe.显然Thread-safe有一定的开销，比如关门，上锁，开门等等。在有些情况下，我们不需要这么safe，比如在家里（如果只有你和你老婆），或者你是单身汉，家里根本就没外人。在这种情况下，不用Thread-safe可能会更方便一些，效率会更高。

StringBuilder就是这样的设计思想。在一切可能的情况下使用StringBuilder，最大限度的提高性能。

大家看看下面这段小程序，就会有些感性认识了。

源程序

......
        String[] strs = null;
        strs = this.prepareString(5000);
        this.stringBufferTest(strs);
        this.stringBuilderTest(strs);
        this.stringTest(strs);
        
        strs = this.prepareString(20000);
        this.stringBufferTest(strs);
        this.stringBuilderTest(strs);
        //this.stringTest(strs);
        
        strs = this.prepareString(100000);
        this.stringBufferTest(strs);
        this.stringBuilderTest(strs);
        //this.stringTest(strs);    
......
    private String[] prepareString(int number){
        System.out.println("String number: " + number);
        String[] strs = new String[number];
        for(int i=0; i<number; i++)
            strs[i] = "Highway" + i;
        return strs;
    }
    private void stringBuilderTest(String[] input){
        long start = System.currentTimeMillis();
        StringBuilder sb = new StringBuilder();
        for(int i=0; i<input.length; i++)
            sb.append(input[i]);
        long time = System.currentTimeMillis()-start;
        System.out.println("StringBuilder Takes Time: " + time + "ms");
        return;
    }
    private void stringBufferTest(String[] input){
        long start = System.currentTimeMillis();
        StringBuffer sb = new StringBuffer();
        for(int i=0; i<input.length; i++)
            sb.append(input[i]);
        long time = System.currentTimeMillis()-start;
        System.out.println("StringBuffer Takes Time: " + time+ "ms");
        return;
    }
    private void stringTest(String[] input){
        long start = System.currentTimeMillis();
        String sb = "";
        for(int i=0; i<input.length; i++)
            sb = sb + input[i];
        long time = System.currentTimeMillis()-start;
        System.out.println("String Append Takes Time: " + time+ "ms");
        return;
    }

反编译得到的程序，这是Java实际工作的Code.

    private String[] prepareString(int number)
    {
        System.out.println((new StringBuilder()).append("String number: ").append(number).toString());
        String strs[] = new String[number];
        for(int i = 0; i < number; i++)
            strs[i] = (new StringBuilder()).append("Highway").append(i).toString();

        return strs;
    }

    private void stringBuilderTest(String input[])
    {
        long start = System.currentTimeMillis();
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < input.length; i++)
            sb.append(input[i]);

        long time = System.currentTimeMillis() - start;
        System.out.println((new StringBuilder()).append("StringBuilder Takes Time: ").append(time).append("ms").toString());
    }

    private void stringBufferTest(String input[])
    {
        long start = System.currentTimeMillis();
        StringBuffer sb = new StringBuffer();
        for(int i = 0; i < input.length; i++)
            sb.append(input[i]);

        long time = System.currentTimeMillis() - start;
        System.out.println((new StringBuilder()).append("StringBuffer Takes Time: ").append(time).append("ms").toString());
    }

    private void stringTest(String input[])
    {
        long start = System.currentTimeMillis();
        String sb = "";
        for(int i = 0; i < input.length; i++)
            sb = (new StringBuilder()).append(sb).append(input[i]).toString();

        long time = System.currentTimeMillis() - start;
        System.out.println((new StringBuilder()).append("String Append Takes Time: ").append(time).append("ms").toString());
    }

由上可见，Java在内部尽可能的在使用StringBuilder

[SIZE=3]测试结果：[/SIZE]

String number: 5000
StringBuffer Takes Time: 15ms
StringBuilder Takes Time: 0ms
String Append Takes Time: 7281ms
String number: 20000
StringBuffer Takes Time: 31ms
StringBuilder Takes Time: 16ms
String number: 100000
StringBuffer Takes Time: 188ms
StringBuilder Takes Time: 156ms

由此可见，StringBuilder 确实是有效果的。最慢的是String直接拼接，效果满上千倍，这是大家应该避免的情况。

那么.NET如何呢？.NET只有一个StringBuilder，没有StringBuffer。这个StringBuilder的Public static变量是Thread-safe的，而instance members却不是。哈哈，有意思吧！！！

将上面Java的程序用.NET写一遍，其运行结果比Java快很多，尤其是赤裸裸的SString拼接（20倍）。这是一个很有趣的问题。希望大家能帮我解释一下为什么！！！

String number: 5000
StringBuilder Takes Time: 0ms
String Append Takes Time: 422ms
String number: 20000
StringBuilder Takes Time: 15ms
String number: 100000
StringBuilder Takes Time: 32ms

C#源程序为：

        private String[] prepareString(int number)
        {
            System.Console.WriteLine("String number: " + number);
            String[] strs = new String[number];
            for(int i=0; i<number; i++)
                strs[i] = "Highway" + i;
            return strs;
        }
        private void stringBuilderTest(String[] input)
        {
            long start = System.Environment.TickCount;
            StringBuilder sb = new StringBuilder();
            for(int i=0; i<input.Length; i++)
                sb.Append(input[i]);
            long time = System.Environment.TickCount - start;
            System.Console.WriteLine("StringBuilder Takes Time: " + time + "ms");
            return;
        }

        private void stringTest(String[] input)
        {
            long start = System.Environment.TickCount;
            String sb = "";
            for(int i=0; i<input.Length; i++)
                sb = sb + input[i];
            long time = System.Environment.TickCount - start;
            System.Console.WriteLine("String Append Takes Time: " + time + "ms");
            return;
        }

反编译后为：

private void stringBuilderTest(string[] input)
{
      long num1 = Environment.TickCount;
      StringBuilder builder1 = new StringBuilder();
      for (int num2 = 0; num2 < input.Length; num2++)
      {
            builder1.Append(input[num2]);
      }
      long num3 = Environment.TickCount - num1;
      Console.WriteLine("StringBuilder Takes Time: " + num3 + "ms");
}
 
private void stringTest(string[] input)
{
      long num1 = Environment.TickCount;
      string text1 = "";
      for (int num2 = 0; num2 < input.Length; num2++)
      {
            text1 = text1 + input[num2];
      }
      long num3 = Environment.TickCount - num1;
      Console.WriteLine("String Append Takes Time: " + num3 + "ms");
}

复 String, StringBuffer &amp;StringBuilder的玄妙
家园 后天我才有时间对你的这个和下面那个问题进行测试

请耐心等待。

我的那个话题目前也只能够暂停了。

复 String, StringBuffer &amp;StringBuilder的玄妙
家园 我对Java StringBuffer/StringBuilder的测试结果

首先，我对老轧的程序进行了一些简单的修改，主要如下：

一。取消了对String的测试部分，而只测试StringBuffer和StringBuilder，因为String的性能明显落后，测试的意义不大。

二。测试范围从1000到100，000，步长为1000，这样可以看出一些比较细的东西。

三。每组测试后，我调用了System.gc()来建议JVM立刻进行内存回收，其目的是最小化前次试验对后续试验由于不定期的内存回收所造成的性能震荡。

其次，我的实验分为使用-Client和-Server两种，目的是比较不同参数下的同级别测试的性能差异，另外，所使用的参数还包括了-Xms256M -Xmx256M。

下面是我的测试代码：

package test2005_2;

class StringTest {

private String[] prepareString(int number) {

System.out.println("String number: " + number);

String[] strs = new String[number];

for (int i = 0; i < number; i++) {

strs[i] = "Highway" + i;

}

return strs;

}

private void stringBuilderTest(String[] input) {

long start = System.currentTimeMillis();

StringBuilder sb = new StringBuilder();

for (int i = 0; i < input.length; i++) {

sb.append(input[i]);

}

long time = System.currentTimeMillis() - start;

System.out.println("StringBuilder Takes Time: " + time + "ms");

}

private void stringBufferTest(String[] input) {

long start = System.currentTimeMillis();

StringBuffer sb = new StringBuffer();

for (int i = 0; i < input.length; i++) {

sb.append(input[i]);

}

long time = System.currentTimeMillis() - start;

System.out.println("StringBuffer Takes Time: " + time + "ms");

}

public void test() {

String[] strs = null;

for (int i = 1; i <= 100; i++) {

strs = this.prepareString(i * 1000);

this.stringBufferTest(strs);

this.stringBuilderTest(strs);

System.gc();

}

}

public static void main(String[] args) {

StringTest stringtest = new StringTest();

stringtest.test();

}

}

下面是使用了-Server -Xms256M -Xmx256M参数情况下的测试结果：

String number: 1000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 2000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 3000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 4000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 0ms

String number: 5000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 6000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 7000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 8000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 9000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 10000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 11000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 12000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 13000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 14000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 15000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 16000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 17000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 18000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 19000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 20000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 21000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 22000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 23000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 24000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 25000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 26000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 27000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 28000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 29000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 31ms

String number: 30000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 31000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 32000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 31ms

String number: 33000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 34000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 35000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 36000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 37000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 38000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 39000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 40000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 41000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 42000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 43000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 44000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 45000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 46000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 47000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 48000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 32ms

String number: 49000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 50000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 15ms

String number: 51000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 31ms

String number: 52000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 15ms

String number: 53000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 54000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 55000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 56000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 57000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 58000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 15ms

String number: 59000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 60000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 61000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 15ms

String number: 62000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 63000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 31ms

String number: 64000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 65000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 66000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 67000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 68000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 69000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 70000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 47ms

String number: 71000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 47ms

String number: 72000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 32ms

String number: 73000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 46ms

String number: 74000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 75000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 32ms

String number: 76000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 31ms

String number: 77000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 32ms

String number: 78000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 31ms

String number: 79000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 80000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 16ms

String number: 81000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 31ms

String number: 82000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 83000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 84000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 85000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 46ms

String number: 86000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 63ms

String number: 87000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 0ms

String number: 88000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 47ms

String number: 89000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 90000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 91000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 92000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 15ms

String number: 93000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 15ms

String number: 94000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 15ms

String number: 95000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 0ms

String number: 96000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 47ms

String number: 97000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 0ms

String number: 98000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 99000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 16ms

String number: 100000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 94ms

下面是使用了 -Client -Xms256M -Xmx256M参数情况下的测试结果：

String number: 1000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 2000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 3000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 4000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 5000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 6000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 7000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 8000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 9000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 10000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 11000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 12000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 13000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 14000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 15000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 16000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 17000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 18000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 19000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 20000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 21000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 22000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 23000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 24000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 25000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 26000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 27000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 28000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 29000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 30000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 0ms

String number: 31000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 32000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 33000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 0ms

String number: 34000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 35000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 36000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 37000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 0ms

String number: 38000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 39000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 40000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 41000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 42000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 43000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 44000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 45000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 46000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 31ms

String number: 47000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 15ms

String number: 48000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 49000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 50000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 51000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 31ms

String number: 52000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 53000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 54000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 16ms

String number: 55000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 62ms

String number: 56000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 63ms

String number: 57000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 63ms

String number: 58000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 62ms

String number: 59000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 47ms

String number: 60000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 47ms

String number: 61000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 63ms

String number: 62000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 63000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 64000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 94ms

String number: 65000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 62ms

String number: 66000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 67000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 68000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 78ms

String number: 69000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 78ms

String number: 70000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 78ms

String number: 71000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 78ms

String number: 72000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 78ms

String number: 73000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 62ms

String number: 74000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 78ms

String number: 75000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 78ms

String number: 76000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 77000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 62ms

String number: 78000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 62ms

String number: 79000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 63ms

String number: 80000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 47ms

String number: 81000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 63ms

String number: 82000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 78ms

String number: 83000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 78ms

String number: 84000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 63ms

String number: 85000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 62ms

String number: 86000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 62ms

String number: 87000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 78ms

String number: 88000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 62ms

String number: 89000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 79ms

String number: 90000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 15ms

String number: 91000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 15ms

String number: 92000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 15ms

String number: 93000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 0ms

String number: 94000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 16ms

String number: 95000

StringBuffer Takes Time: 110ms

StringBuilder Takes Time: 0ms

String number: 96000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 0ms

String number: 97000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 15ms

String number: 98000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 16ms

String number: 99000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 15ms

String number: 100000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 31ms

测试结果概述：

一。对于使用了-Server参数的测试，我们可以看出以下结果：

1。在35000以前，结果是不确定的，也就是说，交替出现了某方为0的结果。

2。从35000到69000，基本是交替领先，领先次数基本是平局。

3。从70000到100000，StringBuffer领先于StringBuilder的比例是22:8。

结论，在这样的测试环境下，StringBuffer的总体表现要比StringBuilder强！

二。对于使用了-Client参数的测试，我们可以看出以下结果：

1。在50000以前，结果是不确定的，也就是说，交替出现了某方为0的结果。

2。从50000到89000，StringBuffer领先于StringBuilder的比例是1:36

3。从90000到100000，StringBuilder领先于StringBuffer的比例是11:0。

结论：本组测试的101组数据中，前五十组可以认为比较失真，后面的五十组StringBuilder领先于StringBuffer的比例是12:36，而且是只有最后的十一组才体现出StringBuilder的优势，因此我们可以得出结论：只有在非常大的字符串数组情况下，StringBuilder的表现才领先于StringBuffer，否则并不占优势。

注：以上测试是在一台运行Windows XP Pro+SP2, 512M内存，Java 1.5，JBuilder 2005 Enterprise的机器上得出的。

复 String, StringBuffer &amp;StringBuilder的玄妙
家园 我对.Net2.0 Beta1下StringBuilder的测试结果

首先，我对老轧的程序进行了一些简单的修改，主要如下：

一。取消了对String的测试部分，而只测试StringBuilder，因为String的性能明显落后，测试的意义不大。

二。测试范围从1000到100，000，步长为1000，这样可以看出一些比较细的东西。

下面是我的测试代码：

#region Using directives

using System;

using System.Collections.Generic;

using System.Text;

#endregion

namespace StringTest

{

class Program

{

private String[] prepareString(int number)

{

System.Console.WriteLine("String number: " + number);

String[] strs = new String[number];

for (int i = 0; i < number; i++)

strs[i] = "Highway" + i;

return strs;

}

private void stringBuilderTest(String[] input)

{

long start = System.Environment.TickCount;

StringBuilder sb = new StringBuilder();

for (int i = 0; i < input.Length; i++)

sb.Append(input[i]);

long time = System.Environment.TickCount - start;

System.Console.WriteLine("StringBuilder Takes Time: " + time + "ms");

return;

}

public void test()

{

String[] strs = null;

for (int i = 1; i <= 100; i++)

{

strs = this.prepareString(i * 1000);

this.stringBuilderTest(strs);

}

}

static void Main(string[] args)

{

Program p = new Program();

p.test();

}

}

}

在将Build结果从Debug设定为Release并且设定目标CPU为x86以后，我得到以下的测试结果：

String number: 1000

StringBuilder Takes Time: 0ms

String number: 2000

StringBuilder Takes Time: 0ms

String number: 3000

StringBuilder Takes Time: 0ms

String number: 4000

StringBuilder Takes Time: 0ms

String number: 5000

StringBuilder Takes Time: 0ms

String number: 6000

StringBuilder Takes Time: 0ms

String number: 7000

StringBuilder Takes Time: 0ms

String number: 8000

StringBuilder Takes Time: 0ms

String number: 9000

StringBuilder Takes Time: 16ms

String number: 10000

StringBuilder Takes Time: 15ms

String number: 11000

StringBuilder Takes Time: 0ms

String number: 12000

StringBuilder Takes Time: 0ms

String number: 13000

StringBuilder Takes Time: 15ms

String number: 14000

StringBuilder Takes Time: 16ms

String number: 15000

StringBuilder Takes Time: 0ms

String number: 16000

StringBuilder Takes Time: 16ms

String number: 17000

StringBuilder Takes Time: 15ms

String number: 18000

StringBuilder Takes Time: 16ms

String number: 19000

StringBuilder Takes Time: 0ms

String number: 20000

StringBuilder Takes Time: 16ms

String number: 21000

StringBuilder Takes Time: 16ms

String number: 22000

StringBuilder Takes Time: 16ms

String number: 23000

StringBuilder Takes Time: 15ms

String number: 24000

StringBuilder Takes Time: 0ms

String number: 25000

StringBuilder Takes Time: 0ms

String number: 26000

StringBuilder Takes Time: 0ms

String number: 27000

StringBuilder Takes Time: 16ms

String number: 28000

StringBuilder Takes Time: 0ms

String number: 29000

StringBuilder Takes Time: 0ms

String number: 30000

StringBuilder Takes Time: 0ms

String number: 31000

StringBuilder Takes Time: 0ms

String number: 32000

StringBuilder Takes Time: 0ms

String number: 33000

StringBuilder Takes Time: 31ms

String number: 34000

StringBuilder Takes Time: 31ms

String number: 35000

StringBuilder Takes Time: 46ms

String number: 36000

StringBuilder Takes Time: 0ms

String number: 37000

StringBuilder Takes Time: 0ms

String number: 38000

StringBuilder Takes Time: 15ms

String number: 39000

StringBuilder Takes Time: 16ms

String number: 40000

StringBuilder Takes Time: 16ms

String number: 41000

StringBuilder Takes Time: 31ms

String number: 42000

StringBuilder Takes Time: 0ms

String number: 43000

StringBuilder Takes Time: 31ms

String number: 44000

StringBuilder Takes Time: 31ms

String number: 45000

StringBuilder Takes Time: 16ms

String number: 46000

StringBuilder Takes Time: 63ms

String number: 47000

StringBuilder Takes Time: 0ms

String number: 48000

StringBuilder Takes Time: 63ms

String number: 49000

StringBuilder Takes Time: 47ms

String number: 50000

StringBuilder Takes Time: 16ms

String number: 51000

StringBuilder Takes Time: 47ms

String number: 52000

StringBuilder Takes Time: 32ms

String number: 53000

StringBuilder Takes Time: 16ms

String number: 54000

StringBuilder Takes Time: 47ms

String number: 55000

StringBuilder Takes Time: 31ms

String number: 56000

StringBuilder Takes Time: 16ms

String number: 57000

StringBuilder Takes Time: 62ms

String number: 58000

StringBuilder Takes Time: 47ms

String number: 59000

StringBuilder Takes Time: 16ms

String number: 60000

StringBuilder Takes Time: 78ms

String number: 61000

StringBuilder Takes Time: 47ms

String number: 62000

StringBuilder Takes Time: 15ms

String number: 63000

StringBuilder Takes Time: 63ms

String number: 64000

StringBuilder Takes Time: 47ms

String number: 65000

StringBuilder Takes Time: 15ms

String number: 66000

StringBuilder Takes Time: 62ms

String number: 67000

StringBuilder Takes Time: 46ms

String number: 68000

StringBuilder Takes Time: 0ms

String number: 69000

StringBuilder Takes Time: 62ms

String number: 70000

StringBuilder Takes Time: 47ms

String number: 71000

StringBuilder Takes Time: 16ms

String number: 72000

StringBuilder Takes Time: 79ms

String number: 73000

StringBuilder Takes Time: 62ms

String number: 74000

StringBuilder Takes Time: 31ms

String number: 75000

StringBuilder Takes Time: 125ms

String number: 76000

StringBuilder Takes Time: 16ms

String number: 77000

StringBuilder Takes Time: 31ms

String number: 78000

StringBuilder Takes Time: 94ms

String number: 79000

StringBuilder Takes Time: 15ms

String number: 80000

StringBuilder Takes Time: 15ms

String number: 81000

StringBuilder Takes Time: 16ms

String number: 82000

StringBuilder Takes Time: 16ms

String number: 83000

StringBuilder Takes Time: 15ms

String number: 84000

StringBuilder Takes Time: 16ms

String number: 85000

StringBuilder Takes Time: 15ms

String number: 86000

StringBuilder Takes Time: 16ms

String number: 87000

StringBuilder Takes Time: 15ms

String number: 88000

StringBuilder Takes Time: 31ms

String number: 89000

StringBuilder Takes Time: 94ms

String number: 90000

StringBuilder Takes Time: 15ms

String number: 91000

StringBuilder Takes Time: 31ms

String number: 92000

StringBuilder Takes Time: 32ms

String number: 93000

StringBuilder Takes Time: 15ms

String number: 94000

StringBuilder Takes Time: 31ms

String number: 95000

StringBuilder Takes Time: 31ms

String number: 96000

StringBuilder Takes Time: 31ms

String number: 97000

StringBuilder Takes Time: 31ms

String number: 98000

StringBuilder Takes Time: 16ms

String number: 99000

StringBuilder Takes Time: 15ms

String number: 100000

StringBuilder Takes Time: 32ms

和我对Java的对应测试相比，测试结果基本等同于Java StringBuilder所对应的结果，不管它是在Server模式下还是Client模式。

注：以上测试结果是在一台运行Windows XP Pro+SP2, 512M内存，Visual Studio 2005 Beta1+.Net 2.0 Beta1的机器上得出的。

复 我对Java StringBuffer/StringBuilder的测试结果
家园 其实这种测试波动很大。因为我们没有办法控制GC.

System.gc()对JVM来说是一个Hint，而不是强制性指令。所以到底什么JVM开始回收内存，是一个不确定的事情。一旦Background thread开始回收内存，前台的程序就会受到极大的影响。这是我们测试的一个难点。

Calling the gc method suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for quick reuse. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all discarded objects.

理论上讲，Thread-safe的操作是有代价的。如果情况允许，我们尽可能避开这个开销！

复 其实这种测试波动很大。因为我们没有办法控制GC.
家园 理论上的确如此

但是我的测试结果并不支持这种看法，而且测试结果的优劣分布还是比较明显的，很多组数据的差距还是比较大的，而不是在临界的+-1。

单独的数据疵点可以认为是JVM作GC所导致的结果，但是这样的数据疵点不应该很多，以至于无法改变最后结果。

另外，我给的内存是256M，对于这样的测试应该是足够的了。

复 理论上的确如此
家园 看看我的测试结果！

StringBuiler几乎是一路领先（低端有些交替）！

java -server -Xmx256M StringTest >perf2.txt

String number: 1000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 2000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 3000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 4000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 0ms

String number: 5000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 6000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 7000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 8000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 9000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 16ms

String number: 10000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 15ms

String number: 11000

StringBuffer Takes Time: 15ms

StringBuilder Takes Time: 0ms

String number: 12000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 13000

StringBuffer Takes Time: 0ms

StringBuilder Takes Time: 0ms

String number: 14000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 15000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 16000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 16ms

String number: 17000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 18000

StringBuffer Takes Time: 16ms

StringBuilder Takes Time: 15ms

String number: 19000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 15ms

String number: 20000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 21000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 22000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 23000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 16ms

String number: 24000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 15ms

String number: 25000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 15ms

String number: 26000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 27000

StringBuffer Takes Time: 32ms

StringBuilder Takes Time: 46ms

String number: 28000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 29000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 32ms

String number: 30000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 31000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 32000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 32ms

String number: 33000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 34000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 47ms

String number: 35000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 32ms

String number: 36000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 47ms

String number: 37000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 47ms

String number: 38000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 47ms

String number: 39000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 47ms

String number: 40000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 47ms

String number: 41000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 16ms

String number: 42000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 43000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 16ms

String number: 44000

StringBuffer Takes Time: 31ms

StringBuilder Takes Time: 31ms

String number: 45000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 46000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 47000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 16ms

String number: 48000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 32ms

String number: 49000

StringBuffer Takes Time: 46ms

StringBuilder Takes Time: 32ms

String number: 50000

StringBuffer Takes Time: 47ms

StringBuilder Takes Time: 31ms

String number: 51000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 63ms

String number: 52000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 63ms

String number: 53000

StringBuffer Takes Time: 63ms

StringBuilder Takes Time: 47ms

String number: 54000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 47ms

String number: 55000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 63ms

String number: 56000

StringBuffer Takes Time: 63ms

StringBuilder Takes Time: 62ms

String number: 57000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 47ms

String number: 58000

StringBuffer Takes Time: 79ms

StringBuilder Takes Time: 62ms

String number: 59000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 63ms

String number: 60000

StringBuffer Takes Time: 63ms

StringBuilder Takes Time: 62ms

String number: 61000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 62ms

String number: 62000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 63ms

String number: 63000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 63ms

String number: 64000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 63ms

String number: 65000

StringBuffer Takes Time: 79ms

StringBuilder Takes Time: 62ms

String number: 66000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 62ms

String number: 67000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 62ms

String number: 68000

StringBuffer Takes Time: 79ms

StringBuilder Takes Time: 62ms

String number: 69000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 78ms

String number: 70000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 63ms

String number: 71000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 63ms

String number: 72000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 62ms

String number: 73000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 62ms

String number: 74000

StringBuffer Takes Time: 78ms

StringBuilder Takes Time: 79ms

String number: 75000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 62ms

String number: 76000

StringBuffer Takes Time: 79ms

StringBuilder Takes Time: 78ms

String number: 77000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 62ms

String number: 78000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 63ms

String number: 79000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 62ms

String number: 80000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 63ms

String number: 81000

StringBuffer Takes Time: 125ms

StringBuilder Takes Time: 47ms

String number: 82000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 47ms

String number: 83000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 84000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 85000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 86000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 47ms

String number: 87000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 88000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 47ms

String number: 89000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 90000

StringBuffer Takes Time: 62ms

StringBuilder Takes Time: 63ms

String number: 91000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 46ms

String number: 92000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 93000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 47ms

String number: 94000

StringBuffer Takes Time: 94ms

StringBuilder Takes Time: 47ms

String number: 95000

StringBuffer Takes Time: 110ms

StringBuilder Takes Time: 47ms

String number: 96000

StringBuffer Takes Time: 109ms

StringBuilder Takes Time: 47ms

String number: 97000

StringBuffer Takes Time: 93ms

StringBuilder Takes Time: 63ms

String number: 98000

StringBuffer Takes Time: 109ms

StringBuilder Takes Time: 47ms

String number: 99000

StringBuffer Takes Time: 109ms

StringBuilder Takes Time: 47ms

String number: 100000

StringBuffer Takes Time: 141ms

StringBuilder Takes Time: 93ms

复 看看我的测试结果！
家园 你试着再加个-Xms256M，看看结果如何？

那就是我的测试结果了。

问题就出在你只限定了最大可用内存而没有限定最小可用内存上面了，缺省的设置是64M，这经常是不够的。在这样的情况下，应用程序迫使JVM多次调用GC和增加可用内存，这样会影响比较结果的。

我的测试方案是首先给足内存（至少是尽可能多的内存，以求减少调用GC和内存膨胀的次数），这样才可以比较真实地进行比较。

Unless you have problems with pauses, try granting as much memory as possible to the virtual machine. The default size (64MB) is often too small.

Setting -Xms and -Xmx to the same value increases predictability by removing the most important sizing decision from the virtual machine. On the other hand, the virtual machine can't compensate if you make a poor choice.

Be sure to increase the memory as you increase the number of processors, since allocation can be parallelized

复 串行化/反串行化小测试中Java取得绝对性胜利！
家园 这个我试验过了，用的是微软自己的例子，结果也一样
复 你试着再加个-Xms256M，看看结果如何？
家园 用不同的参数，运行多次，其结果比较参差。

没有一个一直领先。但大多情况下，StringBuilder要好一些，或者好很多。

java -server -Xms64M -Xmx512M StringTest

StringBuffer Takes Total Time: 1763ms

StringBuilder Takes Total Time: 1127ms

java -server -Xms128M -Xmx256M StringTest

StringBuffer Takes Total Time: 2095ms

StringBuilder Takes Total Time: 952ms

java -server -Xms128M -Xmx512M StringTest

StringBuffer Takes Total Time: 2108ms

StringBuilder Takes Total Time: 888ms

java -server -Xms256M -Xmx512M StringTest

StringBuffer Takes Total Time: 1097ms

StringBuilder Takes Total Time: 1107ms

java -server -Xms512M -Xmx512M StringTest

StringBuffer Takes Total Time: 1235ms

StringBuilder Takes Total Time: 1079ms

缺省下，StringBuilder性能好些。

-Server的连续三次的结果为（总时间）：

StringBuffer Takes Total Time: 5857ms

StringBuilder Takes Total Time: 3984ms

StringBuffer Takes Total Time: 5664ms

StringBuilder Takes Total Time: 3996ms

StringBuffer Takes Total Time: 5772ms

StringBuilder Takes Total Time: 3992ms

-Client的连续三次的结果为（总时间）：

StringBuffer Takes Total Time: 7748ms

StringBuilder Takes Total Time: 6266ms

StringBuffer Takes Total Time: 7845ms

StringBuilder Takes Total Time: 6425ms

StringBuffer Takes Total Time: 7906ms

StringBuilder Takes Total Time: 6307ms

复 【倡议】Java SE 5.0和.NET 2.0擂台赛
家园 两位的二人转很热闹啊

有没兴趣我们搞一个soft 的benchmark 网站?

software 版本的 tomshardware.

复 两位的二人转很热闹啊
家园 这种网站已经不可计数了，何必再搞一个呢？

你有什么别人没有的特色吗？

你能commit多少时间？我们搞这样的网站目的何在？

复 这种网站已经不可计数了，何必再搞一个呢？
家园 俺是不行啊

其实只是想论坛的方式总有它的局限性, 即使老铁

在努力, 有些东西是没法改变的.

需要多种方式互补. 比如这样的专业讨论我觉得用wiki的方式就比较好,

比如你和老兵, 可以共同修改一个文章, 别人也可以修改或者

加注. 有兴趣就写, 没兴趣就不写.

复 俺是不行啊
家园 如果有人出钱，我一定会有积极性。

否则，还是看看球赛，混混日子吧！

复 如果有人出钱，我一定会有积极性。
家园 老兵肯定有积蓄

而且很有事业心的样子..

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