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