String、StringBuffer、StringBuilder的性能测试

个人理解
String 为固定长度的不可变的字符串
StringBuilder 为可变的，且提供个最好的性能，其代码如下

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public StringBuilder append( int i) {        
     super.append(i);        
     return this;        
}    

     public StringBuilder append( int i) {
         super.append(i);
         return this;
    }view plaincopy to clipboardprint?
StringBuffer 为可变的，且提供了同步安全的机制，代码如下<PRE class=java name= "code">     public synchronized StringBuffer append( int i) {        
         super.append(i);        
         return this;        
    }</PRE>        
<PRE class=java name= "code"> </PRE>        
<PRE class=java name= "code">可以看到2个的区别就是StringBuffer是同步的 synchronized </PRE>        
<PRE class=java name= "code"> </PRE>        
<PRE class=java name= "code"><STRONG><FONT size=4>下面是3个性能测试代码</FONT></STRONG></PRE>        
<PRE class=java name= "code"><PRE class=java name= "code"> import java.util.Map;        
    
public class MyTest {        
     /**    
     * @param args    
     */    
     public static void main(String[] args) {        
        testString();        
        testStringBuilder();        
        testStringBufer();        
    }        
    
     static int NUMBER = 10000;        
    
     public static void testString() {        
         long begin = System.currentTimeMillis();        
        String str = "";        
         for ( int i = 1; i < NUMBER; i++) {        
            str = str + i;        
        }        
        System.out.println( "testString=" + (System.currentTimeMillis() - begin));        
    }        
    
     public static void testStringBuilder() {        
         long begin = System.currentTimeMillis();        
        StringBuilder b = new StringBuilder();        
         for ( int i = 1; i < NUMBER; i++) {        
            b.append(i);        
        }        
        String str = b.toString();        
        System.out.println( "testStringBuilder=" + (System.currentTimeMillis() - begin));        
    }        
    
     public static void testStringBufer() {        
         long begin = System.currentTimeMillis();        
        StringBuffer b = new StringBuffer();        
         for ( int i = 1; i < NUMBER; i++) {        
            b.append(i);        
        }        
        String str = b.toString();        
        System.out.println( "testStringBufer=" + (System.currentTimeMillis() - begin));        
    }        
}</PRE>        
<PRE class=java name= "code"> </PRE>        
<PRE class=java name= "code"><STRONG>运行结果如下</STRONG></PRE>        
<PRE class=java name= "code">testString=750<BR>testStringBuilder=0<BR>testStringBufer=0<BR></PRE>        
<PRE class=java name= "code">可见String的操作是非常消耗资源的，而另外2个则性能优异。</PRE>        
<PRE class=java name= "code"> </PRE>        
<PRE class=java name= "code">对于StringBuilder和StringBuffer的对比，就没有必要了。他们的代码相同，只是缺少了同步而已。</PRE>        
<PRE class=java name= "code"> </PRE>        
<PRE class=java name= "code"><STRONG><FONT size=4>结论</FONT></STRONG></PRE>        
<PRE class=java name= "code">大多是情况下，StringBuilder是很好的选择</PRE>        
</PRE>