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TreeSet

程序员文章站 2022-05-14 13:06:30
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特征

1、底层实现是TreeMap, 数据结构是二叉树
2、不保证顺序,但是可以自定义排序、唯一,可为null
3、线程不同步,多线程使用不安全
4、TreeSet集合只能存储可排序的对象
5、如何实现排序

  • 让元素具有排序功能
    元素类实现Comparable接口,重写CompareTo方法
    1.在元素被添加进容器时,会调用compareTo方法和已经存在的元素进行比较
    2.如果返回的int值是正数,这个元素会排在被比较元素的后面
    3.如果返回的int值是负数,这个元素会排在被比较元素的前面
    4.如果返回的int值是0,表示无法比较,这个元素无法添加进容器
  • 让容器具有排序功能
    1.创建一个比较器类,实现Comparator,重写compare方法
    2.使用有参构造创建TreeSet,参数就是比较器类的对象

测试代码

public class Demo02TreeSet {
    @Test
    public void test01(){
        TreeSet<String> set = new TreeSet<>();
        set.add("王子玉");
        set.add("韩文龙");
        set.add("任玉文");
        System.out.println(set);
    }

    @Test
    public void test02(){
        TreeSet<Student> set = new TreeSet<>();
        set.add(new Student("任玉文", 20, '男'));
        set.add(new Student("韩文龙", 30, '女'));
        set.add(new Student("钟雪", 18, '女'));
        System.out.println(set);
    }

    @Test
    public void test03(){

        TeacherComparator teacherComparator = new TeacherComparator();
        TreeSet<Teacher> set = new TreeSet<>(teacherComparator);
        set.add(new Teacher("任玉文", 20, '男'));
        set.add(new Teacher("韩文龙", 30, '女'));
        set.add(new Teacher("钟雪", 18, '女'));
        System.out.println(set);

    }

    @Test
    public void test04(){
        TreeSet<Girlfriend> set = new TreeSet<>();
        set.add(new Girlfriend("a", 90, 20));
        set.add(new Girlfriend("b", 90, 21));
        set.add(new Girlfriend("c", 95, 20));
        set.add(new Girlfriend("d", 95, 21));
        System.out.println(set);

    }
    @Test
    public void test05(){
        GirlfriendComparator girlfriendComparator = new GirlfriendComparator();
        TreeSet<Girlfriend> set = new TreeSet<>(girlfriendComparator);
        set.add(new Girlfriend("a", 90, 20));
        set.add(new Girlfriend("b", 90, 21));
        set.add(new Girlfriend("c", 95, 20));
        set.add(new Girlfriend("d", 95, 21));
        System.out.println(set);

    }

    @Test
    public void test06(){
        Comparator<Girlfriend> comparator = (Girlfriend o1, Girlfriend o2) -> {
           if (o2.getScore() != o1.getScore()){
                return o2.getScore() > o1.getScore() ? 1 : -1;
            }else if (o2.getScore() == o1.getScore()) {
                return o1.getAge() - o2.getAge();
            }else if (o2.getAge() == o1.getAge()){
                return 1;
            } else {
                return 1;
            }
        };
        TreeSet<Girlfriend> set = new TreeSet<>(comparator);
        set.add(new Girlfriend("a", 90, 20));
        set.add(new Girlfriend("b", 90, 21));
        set.add(new Girlfriend("c", 95, 20));
        set.add(new Girlfriend("d", 95, 21));
        System.out.println(set);

    }
}
package org.jgs1904.comparators;

import org.jgs1904.entity.Teacher;

import java.util.Comparator;

/**
 * @ClassName TeacherComparator
 * @Description TODO
 * @Author RenYuWen
 * @Since 2019/12/5 10:06
 */
public class TeacherComparator implements Comparator<Teacher> {
    @Override
    public int compare(Teacher o1, Teacher o2) {
        return o1.getAge() - o2.getAge();
    }
}

package org.jgs1904.comparators;

import org.jgs1904.entity.Girlfriend;

import java.util.Comparator;

/**
 * @ClassName GirlfriendComparator
 * @Description TODO
 * @Author RenYuWen
 * @Since 2019/12/5 10:40
 */
public class GirlfriendComparator implements Comparator<Girlfriend> {
    @Override
    public int compare(Girlfriend o1, Girlfriend o2) {
        if (o2.getScore() != o1.getScore()){
            return o2.getScore() > o1.getScore() ? 1 : -1;
        }else if (o1.getAge() != o2.getAge()) {
            return o1.getAge() - o2.getAge();
        } else {
            return 1;
        }
    }
}
package org.jgs1904.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @ClassName Girlfriend
 * @Description TODO
 * @Author RenYuWen
 * @Since 2019/12/5 10:17
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Girlfriend implements Comparable<Girlfriend>{

    private String name;
    private int score;
    private int age;

    @Override
    public int compareTo(Girlfriend girlfriend) {

        if (girlfriend.getScore() != this.score){
            return girlfriend.getScore() > this.score ? 1 : -1;
        }else if (girlfriend.getScore() == this.score) {
            return this.getAge() - girlfriend.getAge();
        }else if (girlfriend.getAge() == this.getAge()){
            return 1;
        } else {
            return 1;
        }
    }
}

package org.jgs1904.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @ClassName Teacher
 * @Description TODO
 * @Author RenYuWen
 * @Since 2019/12/5 10:00
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher {

    private String name;
    private int age;
    private char sex;

}

相关标签: TreeSet