字符串连接真的那么慢吗？

我目前正在研究String concat选项以及它们对整体性能的惩罚。我的测试用例创造了让我大吃一惊的结果，我不确定我是否忽略了什么。

这是交易：在java中执行操作将（在编译时）每次完成此操作时创建一个新的。"something"+"somethingElse"StringBuilder

对于我的测试用例，我正在从我的HDD加载一个文件，其中包含1661行示例数据（经典的“Lorem Ipsum”）。这个问题不是关于 I/O 性能，而是关于不同字符串连接方法的性能。

public class InefficientStringConcat {

    public static void main(String[] agrs) throws Exception{
        // Get a file with example data:

        System.out.println("Starting benchmark");
        // Read an measure:
        for (int i = 0; i < 10; i++){
            BufferedReader in = new BufferedReader(
                    new InputStreamReader(new FileInputStream(new File("data.txt")))
            );

            long start = System.currentTimeMillis();
            // Un-comment method to test:
            //inefficientRead(in);
            //betterRead(in);
            long end = System.currentTimeMillis();
            System.out.println("Took "+(end-start)+"ms");

            in.close();
        }



    }

    public static String betterRead(BufferedReader in) throws IOException{
        StringBuilder b = new StringBuilder();
        String line;
        while ((line = in.readLine()) != null){
            b.append(line);
        }
        return b.toString();
    }

    public static String inefficientRead(BufferedReader in) throws IOException {
        String everything = "", line;
        while ((line = in.readLine()) != null){
            everything += line;
        }
        return everything;
    }
}

如您所见，两个测试的设置是相同的。结果如下：

使用低效Read（）-方法：

Starting benchmark
#1 Took 658ms
#2 Took 590ms
#3 Took 569ms
#4 Took 567ms
#5 Took 562ms
#6 Took 570ms
#7 Took 563ms
#8 Took 568ms
#9 Took 560ms
#10 Took 568ms

使用 betterRead（）-method

Starting benchmark
#1 Took 42ms
#2 Took 10ms
#3 Took 5ms
#4 Took 7ms
#5 Took 16ms
#6 Took 3ms
#7 Took 4ms
#8 Took 5ms
#9 Took 5ms
#10 Took 13ms

我正在运行测试，没有对-命令有额外的参数。我从2009年初开始运行MacMini3，1和Sun JDK 7：java

[luke@BlackBox ~]$ java -version
java version "1.7.0_09"
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) Client VM (build 23.5-b02, mixed mode)

在我看来，这是一个非常重大的差异。我在衡量这一点时是否做错了什么，或者这应该发生吗？