java中StringBuilder清空效率比较

都知道如果多个字符串拼接的话，用StringBuilder.append会比str+=""效率高很多

因为不用创建string对象和数组拷贝，

在jdk1.5中测试了3中方法清空builder

package com.jb.efile.model;

import java.io.IOException;

public class Test {
private static long time;
public static void main(String[] args) throws IOException {
StringBuilder builder = new StringBuilder();
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));
for(int i=0;i<10000000;i++){
builder.delete(0, builder.length());
builder.append("a");
builder.append("b");
builder.append("c");
builder.append("d");
builder.append("e");
}
System.out.println("delete 耗时：" + (System.currentTimeMillis() - time));
for(int i=0;i<10000000;i++){
builder.setLength(0);
builder.append("1a");
builder.append("1b");
builder.append("1c");
builder.append("1d");
builder.append("1e");
}
System.out.println("setLenth=0 耗时：" + (System.currentTimeMillis() - time));
}
}

输出：

new 耗时：1146
delete 耗时：2268
setLenth=0 耗时：3371

所以本人测试时new效率会高，但是网上很多人测试说delete效率高，希望大家拷贝代码到自己的环境中亲子测试下