【java基础：List和HashMap】给单列集合赋id,并放入双列集合

港控/mmm° 2024-04-03 11:03 56阅读 0赞

要求：

Account账户对象自动分配id;

给定一个List:

List list = new ArrayList();

List.add(new Account(10.00, "1234"));

List.add(new Account(15.00, "15678"));

List.add(new Account(0, "1010"));

要求把List中的内容放到一个Map中，该Map的键为id,值为相应的Account对象；

最后遍历这个Map，打印所有Account对象的id和余额。

Account.java账户类

>     public class Account {
>         private long id;
>         private double balance;
>         private String password;
>         //无参构造方法
>         public Account() {
>         }
>     
>         //含全部参数的构造方法
>         //鼠标右键generate,选择参数，快速构建
>         public Account(long id, double balance, String password) {
>             this.id = id;
>             this.balance = balance;
>             this.password = password;
>         }
>     
>         //含两个参数的构造方法
>         public Account(double balance, String password) {
>             this.balance = balance;
>             this.password = password;
>         }
>     
>         //鼠标右键，toString方法，快速构建
>         @Override
>         public String toString() {
>             return "Account{" +
>                     "id=" + id +
>                     ", balance=" + balance +
>                     ", password='" + password + '\'' +
>                     '}';
>         }
>     
>         //鼠标右键generate，get/set方法，快速构建
>         public long getId() {
>             return id;
>         }
>     
>         public void setId(long id) {
>             this.id = id;
>         }
>     
>         public double getBalance() {
>             return balance;
>         }
>     
>         public void setBalance(double balance) {
>             this.balance = balance;
>         }
>     
>         public String getPassword() {
>             return password;
>         }
>     
>         public void setPassword(String password) {
>             this.password = password;
>         }
>     }

Test99.java测试类

>     import java.util.*;
>     
>     public class Test99 {
>         public static void main(String[] args) {
>             List<Account> list = new ArrayList<Account>();
>             Collections.addAll(list,
>                     //获得当前毫秒数，为id赋值，即获得随机的id
>                     new Account(System.currentTimeMillis(),10.00,"1234"),
>                     new Account(System.currentTimeMillis()+1,15.00,"5678"),
>                     new Account(System.currentTimeMillis()+2,10.00,"1010"));
>     
>             HashMap<Long,Account> map = new HashMap<Long,Account>();
>             //增强for循环
>             //遍历单列集合list，把获得的id和余额a,放进双列集合map
>             for (Account a : list){
>                 map.put(a.getId(),a);
>             }
>             Set<Long> keySet = map.keySet();
>             for (Long k : keySet){
>                 //创建account对象，为account对象赋key值
>                 Account account = map.get(k);
>                 System.out.println("key:"+k+"value:"+account);
>             }
>     
>         }
>     }

运行结果：

![28e3c709e3b1424eb2efab82042d0f78.png][]

[28e3c709e3b1424eb2efab82042d0f78.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/447b1eb53b37453b993ca214ff8c5c0a.png