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Map的简单使用。

年迈的代码机器 2022-02-28 阅读 58

1:首先,Map是Java的一个接口,Map.Entry是Map的一个内部接口。

2:Java类型的使用(要转换类型直接改变Map<?,?>)

    @Test
    //输出Java类型。
    public  void save() {
      Map<String,Object> map = new HashMap<String,Object>();
        map.put("Key1","Value1");
        map.put("Key2","Value2");
        map.put("Key3","Value3");
        map.put("Key4","Value4");
        for(Map.Entry<String,Object> entry : map.entrySet()){
            System.out.println("Key是:  "+entry.getKey()+"    value是:"+entry.getValue());
        }

    }

 3:自定义类型的使用

//创建一个实体类
public class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}


//测试:
    //自定义输出实体类
    @Test
    public void save1(){
       Map<String,User> map =  new HashMap<String,User>();
        map.put("1",new User("username1","password1"));
        map.put("2",new User("username2","password2"));
        map.put("3",new User("username3","password3"));
        map.put("4",new User("username4","password4"));

        for (Map.Entry<String,User> maps : map.entrySet()) {
            System.out.println("key是: " + maps.getKey()+"   value是:  "+maps.getValue());
        }
    }

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