JAVA字符串拼接效率

比较string、stringbuffer、stringbuilder拼接效率

public class MainTest {
	public static void main(String[] args) {
		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..."); 
}
}

输出结果：
Start... 30000
用String+=拼接字符串的时间32800
用String=String+拼接字符串的时间30609
用String.concat拼接字符串的时间14144
用StringBuffer.append拼接字符串的时间2
用StringBuilder.append拼接字符串的时间2
End...