常用的类及API

package boa;

import java.util.Scanner;

public class TestSystem {
public static void main(String[] args) {
    //方法1；输出
    //方法2：退出jvm System.exit(0)
    //方法3:数组复制arraycopy()
    //方法4：获得当前的系统时间；long
    
    /*System.out.println();
    System.err.println();
    
    Scanner s=new Scanner(System.in);
    System.out.println("是否要退出(1/0)");
    int flag=s.nextInt();
    if(flag==1){
        System.out.println("进入此系统");
    }else{
        System.exit(0);
    }
    
    System.out.println("进入之后还要惊喜呢");*/
    
    //数组复制
    long start=System.currentTimeMillis();
    String[] three={"刘备","关羽","张飞","诸葛亮"};
    String[] travel={"唐僧","孙悟空","八戒","沙僧","白骨精","牛魔王","女儿国"};
    for(int i=0;i<1000000;i++){
        System.arraycopy(three, 0, travel, 2, 4);
    }

    
    for(String name:travel){
        System.out.println(name);
    }
    
    long end=System.currentTimeMillis();
    System.out.println("消耗时间："+(end-start));
    
}
}