HashMap的使用

package edu.wtbu;

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

public class Demo01 {
    public static void main(String[] args) {
        //HashMap集合的使用：存储结构：哈希表（数组+链表+红黑树）
        //使用key的hashCode和equals作为重复

        //创建集合
        HashMap<Student, String> hashMap = new HashMap<>();

        //1.添加元素
        Student s1 = new Student("张三", 16);
        Student s2 = new Student("李四", 17);
        Student s3 = new Student("王五", 18);
        hashMap.put(s1,"湖北");
        hashMap.put(s2,"湖南");
        hashMap.put(s3,"深圳");
        //hashMap.put(s3,"上海");
        hashMap.put(new Student("王五", 18),"深圳");
        System.out.println("元素个数："+hashMap.size());//元素个数：3
        System.out.println(hashMap);//{Student{name='王五', stuNo=18}=深圳, Student{name='张三', stuNo=16}=湖北, Student{name='李四', stuNo=17}=湖南}

        //2.删除元素
        hashMap.remove(s1);
        System.out.println("元素个数："+hashMap.size());//元素个数：2
        System.out.println(hashMap);//{Student{name='王五', stuNo=18}=深圳,  Student{name='李四', stuNo=17}=湖南}

        //3.遍历
          //1.使用KeySet
        Set<Student> keySet = hashMap.keySet();
        for (Student key:
                keySet) {
            System.out.println(key+"--------"+hashMap.get(key));
        }

          //2.使用EntrySet
        Set<Map.Entry<Student, String>> entrySet = hashMap.entrySet();
        for (Map.Entry<Student, String> entry:
                entrySet) {
            //System.out.println(entry.getKey()+"-----------"+entry.getValue());
            System.out.println(entry);
        }

        //4.判断
        System.out.println(hashMap.containsKey(s2));//true
        System.out.println(hashMap.isEmpty());//false

    }
}

package edu.wtbu;

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 == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return stuNo == student.stuNo && Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, stuNo);
    }
}