java字符串拼接与性能

使用

• Concatenation Operator (+)
• String concat method – concat(String str)
• StringBuffer append method – append(String str)
• StringBuilder append method – append(String str)

进行性能测试。

环境 win7 32位， cpu双核2.5GHZ，2G内存。

测试代码如下：

    private final static int OUTER_ITERATION = 10;
    private final static int INNER_ITERATION = 50000;

    /**
     * @param args
     */
    public static void main(String[] args) {
        String addTestStr = "";
        String concatTestStr = "";
        StringBuffer concatTestSb = null;
        StringBuilder concatTestSbu = null;

        for (int outerIndex = 0; outerIndex < OUTER_ITERATION; outerIndex++) {
            StopWatch stopWatch = new LoggingStopWatch("StringAddConcat");
            addTestStr = "";
            for (int innerIndex = 0; innerIndex < INNER_ITERATION; innerIndex++)
                addTestStr += "*";
            stopWatch.stop();
        }

        for (int outerIndex = 0; outerIndex < OUTER_ITERATION; outerIndex++) {
            StopWatch stopWatch = new LoggingStopWatch("StringConcat");
            concatTestStr = "";
            for (int innerIndex = 0; innerIndex < INNER_ITERATION; innerIndex++)
                concatTestStr.concat("*");
            stopWatch.stop();
        }

        for (int outerIndex = 0; outerIndex < OUTER_ITERATION; outerIndex++) {
            StopWatch stopWatch = new LoggingStopWatch("StringBufferConcat");
            concatTestSb = new StringBuffer();
            for (int innerIndex = 0; innerIndex < INNER_ITERATION; innerIndex++)
                concatTestSb.append("*");
            stopWatch.stop();
        }

        for (int outerIndex = 0; outerIndex < OUTER_ITERATION; outerIndex++) {
            StopWatch stopWatch = new LoggingStopWatch("StringBuilderConcat");
            concatTestSbu = new StringBuilder();
            for (int innerIndex = 0; innerIndex < INNER_ITERATION; innerIndex++)
                concatTestSbu.append("*");
            stopWatch.stop();
        }

    }

测试结果：
Performance Statistics   2010-04-08 06:16:00 - 2010-04-08 06:16:30

Tag	Avg(ms)	Min	Max	Std Dev	Count
StringAddConcat	9355.4	7860	10046	547.7	10
StringBufferConcat	3.5	0	5	2.3	10
StringBuilderConcat	2.0	0	5	2.4	10
StringConcat	3.1	0	6	2.5	10