Map的实现类：HashMap

在API获取HsahMap类的全部信息

实例代码：创建一个Student类和Demo02

package com.map;

public class Student {
    private String name;
    private int stuNo;

    public Student(String name, int stuNo) {
        this.name = name;
        this.stuNo = stuNo;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getStuNo() {
        return stuNo;
    }

    public void setStuNo(int stuNo) {
        this.stuNo = stuNo;
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", stuNo=" + stuNo + "]";
    }
}

package com.map;

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

/**
 * HashMap集合的使用
 * 存储结构：哈希表(数组+链表+红黑树)
 */
public class Demo02 {
    public static void main(String[] args) {
        //创建集合 key是Student类  value是String类
        HashMap<Student, String> students = new HashMap<>();
        //new 学生实例对象
        Student s1 = new Student("小王", 100);
        Student s2 = new Student("小张",101);
        Student s3 = new Student("小朱",102);
        //1添加元素
        students.put(s1,"北京");
        students.put(s2,"上海");
        students.put(s3,"杭州");
        students.put(s3,"南京"); //添加这个s3会覆盖上面的s3 key不允许重复
        System.out.println("元素个数"+students.size());
        System.out.println(students);
        //2删除
        students.remove(s1);
        System.out.println(students);
        //3遍历
        //3.1使用keySet()
        System.out.println("---------keySet()----- --");
        Set<Student> set = students.keySet();
        for (Student s : set) {
            System.out.println(s);
        }
        //3.2使用entrySet()  Entry是一个映射对 包括一对key和value
        System.out.println("---------entrySet()----- --");
        Set<Map.Entry<Student, String>> entries = students.entrySet();
        for (Map.Entry<Student, String> entry : entries) {
            System.out.println(entry.getKey());
        }
        //4判断
        System.out.println(students.containsKey(s3));
        System.out.println(students.containsValue("北京"));
    }
}

结果：