几种拼接字符串的效率问题 .

public class test { 

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
		long n = 30000;
		System.out.println("Start... "+n);  

        long start1 = System.currentTimeMillis();
        String s1 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s1+="拼接字符串的时间";
        }
        long end1 = System.currentTimeMillis();
        long time1 = end1 -start1;
        System.out.println("用String+=拼接字符串的时间"+time1);   

        long start2 = System.currentTimeMillis();
        String s2 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s2=s2+"拼接字符串的时间";
        }
        long end2 = System.currentTimeMillis();
        long time2 = end2 -start2;
        System.out.println("用String=String+拼接字符串的时间"+time2); 

        long start3 = System.currentTimeMillis();
        String s3 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s3=s3.concat("拼接字符串的时间");
        }
        long end3 = System.currentTimeMillis();
        long time3 = end3 -start3;
        System.out.println("用String.concat拼接字符串的时间"+time3); 

        long start4 = System.currentTimeMillis();
        StringBuffer s4 = new StringBuffer("hello");
        for (long i = 0; i < n; i++)
        {
        	s4.append("拼接字符串的时间");
        }
        long end4 = System.currentTimeMillis();
        long time4 = end4 -start4;
        System.out.println("用StringBuffer.append拼接字符串的时间"+time4);   

        long start5 = System.currentTimeMillis();
        StringBuilder s5 = new StringBuilder("hello");
        for (long i = 0; i < n; i++)
        {
        	s5.append("拼接字符串的时间");
        }
        long end5 = System.currentTimeMillis();
        long time5 = end5 -start5;
        System.out.println("用StringBuilder.append拼接字符串的时间"+time5);   

        System.out.println("End...");
} 

}

贴出一组检测数据如下:

用String+=拼接字符串的时间27468
用String=String+拼接字符串的时间25813
用String.concat拼接字符串的时间12265
用StringBuffer.append拼接字符串的时间14
用StringBuilder.append拼接字符串的时间8