JAVA进阶21

Posted 2021-02-16 贫血的吸血鬼

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

 1 package cn.zjc.mycollection;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 public class TestMap {
 7     public static void main(String[] args) {
 8         Employee e1 = new Employee(101,"王大",200);
 9         Employee e2 = new Employee(102,"王二",201);
10         Employee e3 = new Employee(103,"王仨",202);
11         Employee e4 = new Employee(104,"王四",203);
12 
13         Map<Integer,Employee> map = new HashMap<>();
14 
15         map.put(101,e1);
16         map.put(102,e2);
17         map.put(103,e3);
18         map.put(104,e4);
19         Employee emp = map.get(101);
20         System.out.println(emp.getEname());
21     }
22 }
23 
24 //雇员信息
25 class Employee{
26     private int id;
27     private String ename;
28     private double salary;
29 
30     public int getId() {
31         return id;
32     }
33 
34     public void setId(int id) {
35         this.id = id;
36     }
37 
38     public String getEname() {
39         return ename;
40     }
41 
42     public void setEname(String ename) {
43         this.ename = ename;
44     }
45 
46     public double getSalary() {
47         return salary;
48     }
49 
50     public void setSalary(double salary) {
51         this.salary = salary;
52     }
53 
54     public Employee(int id, String ename, double salary) {
55         this.id = id;
56         this.ename = ename;
57         this.salary = salary;
58 
59     }
60 }

View Code

运行结果图

 3、发红包案例

 1 package cn.intcast.demo16;
 2 
 3 public abstract class User {
 4     private String name;    //姓名
 5     private int money;      //余额，当前用户拥有的钱数
 6 
 7     public User() {
 8     }
 9 
10     public void show(){
11         System.out.println("我叫："+name+",我有:"+money+"元");
12     }
13     public User(String name, int money) {
14         this.name = name;
15         this.money = money;
16     }
17 
18     public String getName() {
19         return name;
20     }
21 
22     public void setName(String name) {
23         this.name = name;
24     }
25 
26     public int getMoney() {
27         return money;
28     }
29 
30     public void setMoney(int money) {
31         this.money = money;
32     }
33 }

User

 1 package cn.intcast.demo16;
 2 
 3 import java.util.ArrayList;
 4 
 5 public class Manager extends User {
 6     public Manager() {
 7 
 8     }
 9 
10     public Manager(String name, int money) {
11         super(name, money);
12     }
13 
14     public ArrayList<Integer> send(int totalMoney, int count) {
15         //首先需要一个集合，用来存储若干个红包的金额
16         ArrayList<Integer> redList = new ArrayList<>();
17 
18         //确认群主用户有多少余额
19         int leftMoney = super.getMoney();
20         if (totalMoney > leftMoney) {
21             System.out.println("余额不足！");
22             return redList;     //返回空集合
23         }
24 
25         //扣钱，重新设置余额
26         super.setMoney(leftMoney - totalMoney);
27 
28         //红包平均拆分成count份
29         int avg = totalMoney / count;
30         //除不尽的余数
31         int mod = totalMoney % count;
32 
33         //将红包一个一个放到集合中
34         for (int i = 0; i < count - 1; i++) {
35             redList.add(avg);
36         }
37         //最后一个红包
38         int last = avg + mod;
39         redList.add(last);
40 
41         return redList;
42     }
43 }

Manager

 1 package cn.intcast.demo16;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Random;
 5 
 6 public class Member extends User {
 7     public Member() {
 8     }
 9 
10     public Member(String name, int money) {
11         super(name, money);
12     }
13 
14     public void receive(ArrayList<Integer> list) {
15         //从多个红包中随机抽取一个
16         //随机获取一个集合中的索引编号
17         int index = new Random().nextInt(list.size());
18         //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
19         int delta = list.remove(index);
20         //当前成员自己本来有多少钱
21         int money = super.getMoney();
22         //加法，并且重新设置回去
23         super.setMoney(money + delta);
24     }
25 }

Member

 1 package cn.intcast.demo16;
 2 
 3 import java.util.ArrayList;
 4 
 5 public class MainRedPacket {
 6     public static void main(String[] args) {
 7         Manager manager = new Manager("群主",100);
 8         Member one = new Member("成员A",10);
 9         Member two = new Member("成员B",10);
10         Member three = new Member("成员C",10);
11 
12         manager.show();
13         one.show();
14         two.show();
15         three.show();
16         System.out.println("===============");
17 
18         //群主总共发32，分成3包
19         ArrayList<Integer> redList = manager.send(32,3);
20         //三个成员收红包
21         one.receive(redList);
22         two.receive(redList);
23         three.receive(redList);
24         manager.show();
25         one.show();
26         two.show();
27         three.show();
28     }
29 }

MainRedPacket

运行结果图