java String StringBuffer StringBuilder执行速度区别

long s1 = System.currentTimeMillis();
        int n = 10000;
        String str = "";
        for (int i = 0; i < n; i++) {
            str += ("-" + i);
        }
        System.out.println("String使用的时间为" + (System.currentTimeMillis() - s1) / 1000.0 + "s");

        long s2 = System.currentTimeMillis();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            sb.append("-" + i);
        }
        System.out.println("StringBuilder使用的时间为" + (System.currentTimeMillis() - s2) / 1000.0 + "s");

        long s3 = System.currentTimeMillis();
        StringBuffer sbf = new StringBuffer();
        for (int i = 0; i < n; i++) {
            sbf.append("-" + i);
        }
        System.out.println("StringBuffer使用的时间为" + (System.currentTimeMillis() - s3) / 1000.0 + "s");

执行结果如下StringBuilder>StringBuffer>String 

如果把n加个0 变成100000，可见String真的很慢

仅为了学习记录，勿喷