java System

1、获取系统当前的时间(毫秒)

与Date类中getTime()方法相似

package cn.wt.day12;

import java.util.Date;

public class Demon03 {
    public static void main(String[] args) {
        long systemTime = System.currentTimeMillis();
        System.out.println(systemTime);
        Date date = new Date();
        System.out.println(date.getTime());
    }
}

2、数组copy

语法(看源码注释)

arraycopy(Object src,  int  srcPos, Object dest, int destPos, int length)

src 原数组

srcPos 原数组的index

dest 目标数组

destPos 目标数组的index

length 替换的长度

例子

package cn.wt.day12;


import java.util.Arrays;
import java.util.Objects;

public class Demon03 {
    public static void main(String[] args) {
        long currentTime = System.currentTimeMillis();
        System.out.println(currentTime);

        int[] src = {1, 2, 3, 4, 5, 6};
        int[] dest = {6, 5, 4, 3, 2, 1};
        System.out.println(Arrays.toString(dest));  // [6, 5, 4, 3, 2, 1]
        System.arraycopy(src, 0, dest, 0, 3);
        System.out.println(Arrays.toString(dest)); // [1, 2, 3, 3, 2, 1]
    }
}