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;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", stuNo=" + stuNo +'}';}@Overridepublic 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());}@Overridepublic 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trueSystem.out.println(students.containsValue("东营")); //输出false}
}