java2e performance guides的一点疑问

最新推荐文章于 2021-02-12 11:21:42 发布

原创最新推荐文章于 2021-02-12 11:21:42 发布 · 128 阅读

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文章标签：

#performance

本文通过实验对比了三种创建字符串的方法：直接赋值、使用new关键字和结合String.intern()方法的性能差异。结果显示，在不同环境下，各种方法的效率有所不同。


String variables[] = new String[50000];
for( int i=0;i<variables.length;i++){
variables[i] = "s"+i;
}
// create String literals
long startTime0 = System.currentTimeMillis();
for(int i=0;i<variables.length;i++){
variables[i] = "hello";
}
long endTime0 = System.currentTimeMillis();
System.out.println("Time taken for creation of String literals : "
+ (endTime0 - startTime0) + " milli seconds" );
// create String objects using 'new' keyword
long startTime1 = System.currentTimeMillis();
for(int i=0;i<variables.length;i++){
variables[i] = new String("hello");
}
long endTime1 = System.currentTimeMillis();
System.out.println("Time taken for creation of String objects with 'new' key word : "
+ (endTime1 - startTime1)+" milli seconds");
long startTime2 = System.currentTimeMillis();
for(int i=0;i<variables.length;i++){
variables[i] = new String("hello");
variables[i] = variables[i].intern();
}
long endTime2 = System.currentTimeMillis();
System.out.println("Time taken for creation of String objects with intern(): "
+ (endTime2 - startTime2)+" milli seconds");

这段代码在文章中给出的结果为:
Time taken for creation of String literals : 0 milli seconds
Time taken for creation of String objects with 'new' key word : 160 milli seconds
Time taken for creation of String objects with intern(): 60 milli seconds
但是我在电脑上实际运行结果为:
Time taken for creation of String literals : 0 milli seconds
Time taken for creation of String objects with 'new' key word : 3 milli seconds
Time taken for creation of String objects with intern(): 7 milli seconds
刨除硬件运行速度差异,明显区别还是String.intern()执行到底有没有带来效率上的提高.似乎我的运行结果与作者要说明的事实恰恰相反.