String，StringBuilder字符串拼接性能问题

这是源程序：

String s = "";
		for (int i = 0; i < 50000; i ++)
		{
			s += i;
		}
		
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 50000; i ++)
		{
			sb.append(i);
		}
		StringBuilder sb2 = new StringBuilder();
		for (int i = 0; i < 50000; i ++)
		{
			sb2.append("s" + i);
		}
		
		String s3 = "";
		for (int i = 0; i < 50000; i ++)
		{
			s3 = s3.concat(String.valueOf(i));
		}
		String s4 = "";
		for (int i = 0; i < 50000; i ++)
		{
			s4 = s4.concat("s" + String.valueOf(i));
		}

这是javac编译后的.class文件代码：

        String s = "";
        for(int i = 0; i < 50000; i++)
            s = (new StringBuilder()).append(s).append(i).toString();

        StringBuilder stringbuilder = new StringBuilder();
        for(int j = 0; j < 50000; j++)
            stringbuilder.append(j);

        StringBuilder stringbuilder1 = new StringBuilder();
        for(int k = 0; k < 50000; k++)
            stringbuilder1.append((new StringBuilder()).append("s").append(k).toString());

        String s1 = "";
        for(int l = 0; l < 50000; l++)
            s1 = s1.concat(String.valueOf(l));

        String s2 = "";
        for(int i1 = 0; i1 < 50000; i1++)
            s2 = s2.concat((new StringBuilder()).append("s").append(String.valueOf(i1)).toString());

先留着，下班后过来总结下！