java stringbuilder 清空问题

我也是碰到了这个问题才开始研究的，网上答案偏多，并且时间范围也比较大，各个版本的java 优化也不清楚，只能说我的java环境是1.7，测试给大家看。

三种思想

1、新生成一个，旧的由系统自动回收

2、delete 方法

builder1.delete(0, builder.length());

3、Length

StringBuilder val = new StringBuilder();

val.Append(“….”);

val.Length = 0;//清空

代码

StringBuilder builder = new StringBuilder();

long time = System.currentTimeMillis();

for(int i=0;i<10000000;i++){

builder = new StringBuilder();

builder.append("aa");

builder.append("bb");

builder.append("cc");

builder.append("dd");

builder.append("ee");

}

System.out.println("new 耗时：" + (System.currentTimeMillis() - time));

long time1 = System.currentTimeMillis();

StringBuilder builder1 = new StringBuilder();

for(int i=0;i<10000000;i++){

builder1.delete(0, builder.length());

builder1.append("a");

builder1.append("b");

builder1.append("c");

builder1.append("d");

builder1.append("e");

}

System.out.println("delete 耗时：" + (System.currentTimeMillis() - time1));

long time2 = System.currentTimeMillis();

StringBuilder builder2 = new StringBuilder();

for(int i=0;i<10000000;i++){

builder2.setLength(0);

builder2.append("1a");

builder2.append("1b");

builder2.append("1c");

builder2.append("1d");

builder2.append("1e");

}

System.out.println("setLenth=0 耗时：" + (System.currentTimeMillis() - time2));

结果一：

new 耗时：485

delete 耗时：471

setLenth=0 耗时：385

结果二：

new 耗时：621

delete 耗时：411

setLenth=0 耗时：423

总结

方法二和方法三耗时是差不多的，每次运行花费的时间是不一样的，目前没有去计算每一种方法所占用的资源分别是多少