java中调用System.currentTimeMillis()获取当前时间来求出时间差及程序执行的时间

package com.test;

import java.util.Scanner;
//String的连接1000次
class StringOperate{
private String str;
public long doWork(){
long begin=System.currentTimeMillis();//开始时间
setStr(null);
for(int i=0;i<10000;i++){
setStr(getStr() + i);
}
long end=System.currentTimeMillis();//结束时间
long time=end-begin;//时间差
return time;
}
public String getStr() {
return str;
}
public void setStr(String str) {
this.str = str;
}
}
class IntOperate{
private int num=0;
public long doWork(){
long begin=System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
setNum(getNum() + i);
}
long end=System.currentTimeMillis();
long time=end=begin;
return time;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
}
//模板方法设计模式
class TemplateMethosDemo{

}
public class Main{
private static Scanner sc;

public static void main(String[] args){
//统计String连接10000次此时和int相加的时间差
StringOperate st=new StringOperate();
System.out.println(st.doWork());
IntOperate in=new IntOperate();
System.out.println(in.doWork());
}
}