Map接口_HashMap常用的方法

package Map;

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

/**
 * 测试HashMap的使用
 */
public class TestMap {
    public static void main(String[] args) {
        Map<Integer,String> map=new HashMap<>();
        //增加
        map.put(1,"one");
        map.put(2,"two");
        map.put(3,"three");
        //获取
        System.out.println(map.get(1));
        System.out.println(map.size());
        System.out.println(map.isEmpty());
        System.out.println(map.containsKey(1));
        System.out.println(map.containsValue("four"));

        Map<Integer,String> m1=new HashMap<>();
        m1.put(4,"four");
        map.putAll(m1);
        System.out.println(map);
        //map中键不能重复，如果重复（是否重复根据equals方法），新的值会覆盖旧的值
        map.put(3,"five");
        System.out.println(map);
    }
}

二、泛型时对象

package Map;

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

public class TestMap2 {
    public static void main(String[] args) {
        Map<Integer,Student> m1=new HashMap<>();
        m1.put(1001,new Student(10001,"小明",3000));
        Student s1=m1.get(1001);
        System.out.println(s1.getName());
    }
}




class Student{
    int id;
    String name;
    int salary;

    public int getId() {
        return id;
    }

    public int getSalary() {
        return salary;
    }

    public String getName() {
        return name;
    }
    public Student(int id,String name,int salary){
        this.id=id;
        this.name=name;
        this.salary=salary;
    }

    @Override
    public String toString() {
        return "id"+id+"名字"+name+"薪水"+salary;
    }
}