HashSet

HashSet

Hashset底层是哈希表即数组+链表+红黑树
存储过程：
由hashcode计算数据存储的位置，如果该位置为null,将数据添加进去，否则计算equals若为true，则不添加，否则与链表下一个元素进行equals比较

实践

添加，删除，遍历，判断跟List接口很相近
差别在于如果新建一个赋值完全相同的实例，想要认为其与原实例相同，需要重写equals和hashcode方法，而List中仅需要重写equals

package com.qianfeng.collection;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Objects;

/**
 * 功能描述
 *
 * @since 2022-05-13
 */
public class HashSetDemo {
    public static void main(String[] args) {
        HashSet hashSet = new HashSet();
        Person person = new Person("zhangsan", 1);
        Person person1 = new Person("lisi", 2);
        Person person2 = new Person("wangwu", 3);
        hashSet.add(person);
        hashSet.add(person1);
        hashSet.add(person2);

        hashSet.remove(person2);

        Iterator iterator = hashSet.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

        System.out.println(hashSet.isEmpty());
        System.out.println(hashSet.contains(person));
        System.out.println(hashSet.contains(new Person("zhangsan", 1)));

    }
}

class Person {
    private String name;

    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

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

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        Person person = (Person) o;
        return Objects.equals(name, person.name) && Objects.equals(age, person.age);
    }

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