我也读过这个字符串的.concat方法是最糟糕的choice all the time(这么多,所以它被修改为一个错误Findbugs！).

所以我决定自己在Eclipse中写一个java类.我的结果让我感到惊讶我发现,不同的方法比较快或慢,如果我遵守和运行它们在日食和命令行.

首先我的日食结果是：

the total millis to concatenate with + was: 12154
the total millis to concatenate with .concat was: 8840
the total millis to concatenate with StringBuilder was: 11350
the total millis to concatenate with StringBuilder with a specified size was: 5611

所以在eclipse的StringBuilder中,指定的大小是最快的,其次是.concat(奇怪的),那么StringBuilder和“”连接几乎是一样的.

然而,我在命令行上的结果是：

the total millis to concatenate with + was: 4139
the total millis to concatenate with .concat was: 8590
the total millis to concatenate with StringBuilder was: 10888
the total millis to concatenate with StringBuilder with a specified size was: 6033

所以当我从commnad行编译并运行时,“”运算符显然是最快的,其次是String builder的大小,然后是concat,最后是正常的StringBuilder！

这对我来说没有意义.显然所有的stackoverflow答案我读到说操作符编译成正常的旧StringBuilder实例必须是过时的.

有人知道这里真的发生了什么吗？

我正在使用jdk1.7.0_07,只要我能告诉eclipse和我的命令行都引用了完全相同的一个.我所知道的唯一的区别就是使用“javaw”,但是从我所看到的,这不应该有所作为.

这是我的测试类,如果你想验证我没有做错什么,但我很确定它是坚实的.

public class Test {

    static final int LOOPS = 100000000;
    static final String FIRST_STRING = "This is such";
    static final String SECOND_STRING = " an awesomely cool ";
    static final String THIRD_STRING = "to write string.";

    /**
     * @param args
     */
    public static void main(String[] args) {

        Test.plusOperator();
        Test.dotConcat();
        Test.stringBuilder();
        Test.stringBuilderSizeSpecified();

    }

    public static void plusOperator() {
        String localOne = FIRST_STRING;
        String localTwo = SECOND_STRING;
        String localThree = THIRD_STRING;

        Calendar startTime = Calendar.getInstance();
        for (int x = 0; x < LOOPS; x++) {
            String toPrint = localOne + localTwo + localThree;
        }
        Calendar endTime = Calendar.getInstance();
        System.out.println("the total millis to concatenate with + was: " + 
                (endTime.getTimeInMillis() - startTime.getTimeInMillis()));
    }

    public static void stringBuilder() {
        String localOne = FIRST_STRING;
        String localTwo = SECOND_STRING;
        String localThree = THIRD_STRING;

        Calendar startTime = Calendar.getInstance();
        for (int x = 0; x < LOOPS; x++) {
            StringBuilder toBuild = new StringBuilder()
                .append(localOne)
                .append(localTwo)
                .append(localThree);
        }
        Calendar endTime = Calendar.getInstance();
        System.out.println("the total millis to concatenate with StringBuilder was: " + 
                (endTime.getTimeInMillis() - startTime.getTimeInMillis()));
    }

    public static void stringBuilderSizeSpecified() {
        String localOne = FIRST_STRING;
        String localTwo = SECOND_STRING;
        String localThree = THIRD_STRING;

        Calendar startTime = Calendar.getInstance();
        for (int x = 0; x < LOOPS; x++) {
            StringBuilder toBuild = new StringBuilder(50)
                .append(localOne)
                .append(localTwo)
                .append(localThree);
        }
        Calendar endTime = Calendar.getInstance();
        System.out.println("the total millis to concatenate with StringBuilder with a specified size was: " + 
                (endTime.getTimeInMillis() - startTime.getTimeInMillis()));
    }

    public static void dotConcat() {
        String localOne = FIRST_STRING;
        String localTwo = SECOND_STRING;
        String localThree = THIRD_STRING;

        Calendar startTime = Calendar.getInstance();
        for (int x = 0; x < LOOPS; x++) {
            String toPrint = localOne.concat(localTwo).concat(localThree);
        }
        Calendar endTime = Calendar.getInstance();
        System.out.println("the total millis to concatenate with .concat was: " + 
                (endTime.getTimeInMillis() - startTime.getTimeInMillis()));
    }

}