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;
     }
 }

User

 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;
     }
 }

Manager

 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);
     }
 }

Member

 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();
     }
 }

MainRedPacket

运行结果图