JAVA进阶21

1、Vector向量

如何选用ArrayList、LinkedList、Vector？

①需要线程安全时，用Vector

②不存在线程安全问题时，并且查找较多用ArrayList（一般使用它）

③不存在线程安全问题时，增加或删除元素较多用LinkedList

2、Map的用法

package cn.zjc.mycollection;

import java.util.HashMap;
import java.util.Map;

public class TestMap {
    public static void main(String[] args) {
        Employee e1 = new Employee(101,"王大",200);
        Employee e2 = new Employee(102,"王二",201);
        Employee e3 = new Employee(103,"王仨",202);
        Employee e4 = new Employee(104,"王四",203);

        Map<Integer,Employee> map = new HashMap<>();

        map.put(101,e1);
        map.put(102,e2);
        map.put(103,e3);
        map.put(104,e4);
        Employee emp = map.get(101);
        System.out.println(emp.getEname());
    }
}

//雇员信息
class Employee{
    private int id;
    private String ename;
    private double salary;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public Employee(int id, String ename, double salary) {
        this.id = id;
        this.ename = ename;
        this.salary = salary;

    }
}

运行结果图

 3、发红包案例

package cn.intcast.demo16;

public abstract class User {
    private String name;    //姓名
    private int money;      //余额，当前用户拥有的钱数

    public User() {
    }

    public void show(){
        System.out.println("我叫："+name+",我有:"+money+"元");
    }
    public User(String name, int money) {
        this.name = name;
        this.money = money;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getMoney() {
        return money;
    }

    public void setMoney(int money) {
        this.money = money;
    }
}

package cn.intcast.demo16;

import java.util.ArrayList;

public class Manager extends User {
    public Manager() {

    }

    public Manager(String name, int money) {
        super(name, money);
    }

    public ArrayList<Integer> send(int totalMoney, int count) {
        //首先需要一个集合，用来存储若干个红包的金额
        ArrayList<Integer> redList = new ArrayList<>();

        //确认群主用户有多少余额
        int leftMoney = super.getMoney();
        if (totalMoney > leftMoney) {
            System.out.println("余额不足！");
            return redList;     //返回空集合
        }

        //扣钱，重新设置余额
        super.setMoney(leftMoney - totalMoney);

        //红包平均拆分成count份
        int avg = totalMoney / count;
        //除不尽的余数
        int mod = totalMoney % count;

        //将红包一个一个放到集合中
        for (int i = 0; i < count - 1; i++) {
            redList.add(avg);
        }
        //最后一个红包
        int last = avg + mod;
        redList.add(last);

        return redList;
    }
}

package cn.intcast.demo16;

import java.util.ArrayList;
import java.util.Random;

public class Member extends User {
    public Member() {
    }

    public Member(String name, int money) {
        super(name, money);
    }

    public void receive(ArrayList<Integer> list) {
        //从多个红包中随机抽取一个
        //随机获取一个集合中的索引编号
        int index = new Random().nextInt(list.size());
        //根据索引，从集合当中删除，并且得到被删除的红包，给我自己
        int delta = list.remove(index);
        //当前成员自己本来有多少钱
        int money = super.getMoney();
        //加法，并且重新设置回去
        super.setMoney(money + delta);
    }
}

package cn.intcast.demo16;

import java.util.ArrayList;

public class MainRedPacket {
    public static void main(String[] args) {
        Manager manager = new Manager("群主",100);
        Member one = new Member("成员A",10);
        Member two = new Member("成员B",10);
        Member three = new Member("成员C",10);

        manager.show();
        one.show();
        two.show();
        three.show();
        System.out.println("===============");

        //群主总共发32，分成3包
        ArrayList<Integer> redList = manager.send(32,3);
        //三个成员收红包
        one.receive(redList);
        two.receive(redList);
        three.receive(redList);
        manager.show();
        one.show();
        two.show();
        three.show();
    }
}

运行结果图