TreeSet

TreeSet

概述

TreeSet是一种有序，无脚标，不可重复的集合
底层是红黑树，是一种平衡二叉树

TreeSet对集合中元素如果是自定义类，实现排序有两种方法

1.自定义类继承Comparable接口
2.TreeSet构造方法参数中创建Comparator的匿名类,用于定制排序规则
注意：TreeSet中元素为自定义类的，要让两个内容相同的类为同一个类无需重写equals,也不用重写hashcode,相同由比较规则决定，当比较结果为0时，认为两个元素相同

实现Comparable接口

package com.qianfeng.collection;

import java.util.Iterator;
import java.util.TreeSet;

/**
 * 功能描述
 *
 * @since 2022-05-13
 */
public class TreeSetDemo {
    public static void main(String[] args) {
        TreeSet<Person1> treeSet = new TreeSet();
        Person1 person = new Person1("zhangsan", 1);
        Person1 person1 = new Person1("lisi", 2);
        Person1 person2 = new Person1("wangwu", 3);
        treeSet.add(person);
        treeSet.add(person1);
        treeSet.add(person2);

        System.out.println(treeSet);
        treeSet.remove(new Person1("wangwu", 3));

        Iterator<Person1> iterator = treeSet.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next().getName());
        }

        System.out.println(treeSet.isEmpty());
        System.out.println(treeSet.contains(new Person1("lisi", 2)));

    }
}


class Person1 implements Comparable<Person1> {
    private String name;

    private Integer age;

    public Person1(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 int compareTo(Person1 o) {
        int n1 = name.compareTo(o.name);
        int n2 = age - o.age;
        return n1 == 0 ? n2 : n1;
    }
}

构造Comparator匿名内部类

package com.qianfeng.collection;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/**
 * 功能描述
 *
 * @since 2022-05-13
 */
public class TreeSetDemo2 {
    public static void main(String[] args) {
        TreeSet<Person1> person1s = new TreeSet<>(new Comparator<Person1>() {

            @Override
            public int compare(Person1 o1, Person1 o2) {
                int n1 = o1.getAge() - o2.getAge();
                int n2 = o1.getName().compareTo(o2.getName());
                return n1 == 0 ? n2 : n1;
            }
        });

        Person1 person = new Person1("zhangsan", 1);
        Person1 person1 = new Person1("lisi", 2);
        Person1 person2 = new Person1("wangwu", 3);
        person1s.add(person);
        person1s.add(person1);
        person1s.add(person2);

        System.out.println(person1s);
        person1s.remove(new Person1("zhangsan", 1));

        Iterator<Person1> it = person1s.iterator();
        while (it.hasNext()) {
            System.out.println(it.next().getName());
        }

        System.out.println(person1s.isEmpty());
        person1s.contains(new Person1("wangwu", 3));

    }
}