HashSet的使用以及存储方式

package edu.wtbu;
import java.util.HashSet;
import java.util.Iterator;

public class Demo01 {
    public static void main(String[] args) {
        //HashSet: 存储结构：哈希表（数组+链表+红黑树）
        //存储过程：1.根据hashCode计算保存的位置，如果此位置为空，则直接保存；如果不为空，则执行equals方法，如果equals方法为true，则认为是重复，否则形成链表

        //创建集合
        HashSet<String> hashSet = new HashSet<>();

        //1.添加元素
        hashSet.add("张三");
        hashSet.add("李四");
        hashSet.add("王五");
        hashSet.add("老六");
        //hashSet.add("老六");  重复，不能添加
        System.out.println("元素个数："+hashSet.size());//元素个数：4
        System.out.println(hashSet);//[李四, 张三, 老六, 王五]

        //2.删除元素
        hashSet.remove("老六");
        System.out.println("元素个数："+hashSet.size());//元素个数：3
        System.out.println(hashSet);//[李四, 张三, 王五]

        //3.遍历
          //1.增强for
        for (String s:
             hashSet) {
            System.out.println(s);
        }

          //2.使用迭代器
        Iterator<String> iterator = hashSet.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }

        //4.判断
        System.out.println(hashSet.contains("张三"));//true
        System.out.println(hashSet.isEmpty());//false

        System.out.println("==============================");
        //创建集合
        HashSet<Student> hashSet1 = new HashSet<>();

        //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);
        hashSet1.add(s1);
        hashSet1.add(s2);
        hashSet1.add(s3);
        hashSet1.add(new Student("王五", 18));
        //hashSet1.add(s3); 重复，不能添加
        System.out.println("元素个数："+hashSet1.size());//元素个数：3
        System.out.println(hashSet1);//[Student{name='张三', age=16}, Student{name='李四', age=17}, Student{name='王五', age=18}]

        //2.删除元素
        //hashSet1.remove(s1);
        hashSet1.remove(new Student("张三", 16));
        System.out.println("元素个数："+hashSet1.size());//元素个数：2
        System.out.println(hashSet1);//[Student{name='李四', age=17}, Student{name='王五', age=18}]

        //3.遍历
          //1.增强for
        for (Student s:
             hashSet1) {
            System.out.println(s);
        }

          //2.使用迭代器
        Iterator<Student> iterator1 = hashSet1.iterator();
        while (iterator1.hasNext()){
            System.out.println(iterator1.next());
        }

        //4.判断
        System.out.println(hashSet1.contains(s2));//true
        System.out.println(hashSet1.isEmpty());//false
    }
}

package edu.wtbu;

import java.util.Objects;

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

    public Student() {

    }

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

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

//    @Override
//    public int hashCode() {
//        int n1 = this.name.hashCode();
//        int n2 = this.age;
//        return n1+n2;
//    }
//
//    @Override
//    public boolean equals(Object obj) {
//        if(obj==this){
//            return false;
//        }
//        if(obj==null){
//            return  false;
//        }
//        if(obj instanceof Student){
//            Student s = (Student) obj;
//            if(this.name.equals(s.getName())&&this.age==s.getAge()){
//                return  true;
//            }
//        }
//        return  false;
//    }

    //快捷键：Alt+insert+equals and (hashCode)
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Objects.equals(name, student.name);
    }

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