集合框架16：HashMap的使用

视频链接：13.35 HashMap使用（1）_哔哩哔哩_bilibilihttps://www.bilibili.com/video/BV1zD4y1Q7Fw?spm_id_from=333.788.videopod.episodes&vd_source=b5775c3a4ea16a5306db9c7c1c1486b5&p=35

1.创建Student类，添加无参构造器、有参构造器、get（）和set（）方法、重写hashCode（）方法和equals（）方法；

package com.yundait.demo02;

import java.util.Objects;

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

    public Student() {
    }

    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 +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Student)) return false;
        Student student = (Student) o;
        return getStuNo() == student.getStuNo() && Objects.equals(getName(), student.getName());
    }

    @Override
    public int hashCode() {
        return Objects.hash(getName(), getStuNo());
    }
}

2.创建HashMap类并演示添加元素、删除元素、遍历集合、判断操作

package com.yundait.demo02;

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

public class HashMapDemo01 {
    public static void main(String[] args) {
        //创建HashMap集合

        HashMap<Student, String> students = new HashMap<>();

        //1添加元素

        Student s1 = new Student("孙悟空", 100);
        Student s2 = new Student("猪八戒", 101);
        Student s3 = new Student("沙和尚", 102);

        students.put(s1,"北京");
        students.put(s2,"南京");
        students.put(s3,"杭州");
        students.put(new Student("孙悟空", 100),"杭州");


        System.out.println("元素个数为：" + students.size());
        System.out.println(students.toString());

        //2删除元素

//        students.remove(s1);
        System.out.println("删除后元素的个数：" + students.size());
        System.out.println(students.toString());

        //3遍历元素
        //3.1使用keySet（）方法遍历
        System.out.println("-------使用keySet（）方法遍历-------");
        for(Student key : students.keySet()){
            System.out.println(key + "------------" + students.get(key));
        }

        //3.2使用entrySet（）方法进行遍历
        System.out.println("-----使用entrySet（）方法遍历--------");
        for (Map.Entry<Student, String> entry : students.entrySet()) {
            System.out.println(entry.getKey() + "------------" + entry.getValue());
        }

        //4判断元素
        System.out.println(students.containsKey(s1));  //输出true
        //因为重写了hashCode()和equals方法所以可以判定为相同元素
        System.out.println(students.containsKey(new Student("孙悟空", 100))); //输出true
        System.out.println(students.containsValue("东营")); //输出false


    }
}