TreeSet的使用以及Comparator接口

package edu.wtbu;

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

public class Demo01 {
    public static void main(String[] args) {
       //TreeSet:存储结构：红黑树
        //要求：元素必须实现Comparable接口，compareTo(); 方法的返回值为0，认为是重复元素
        //创建集合
        TreeSet<String> treeSet = new TreeSet<>();

        //1.添加元素
        treeSet.add("xyz");
        treeSet.add("abc");
        treeSet.add("hello");
        treeSet.add("xyz");//重复，不再添加
        System.out.println("元素个数："+treeSet.size());//元素个数：3
        System.out.println(treeSet);//[abc, hello, xyz]

        //2.删除元素
        treeSet.remove("xyz");
        System.out.println("元素个数："+treeSet.size());//元素个数：2
        System.out.println(treeSet);//[abc, hello]

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

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

        //4.判断
        System.out.println(treeSet.contains("abc"));//true
        System.out.println(treeSet.isEmpty());//false

        System.out.println("==============================");
        TreeSet<Student> treeSet1 = new TreeSet<>();

        //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);
        Student s4 = new Student("王五", 19);
        Student s5 = new Student("王五", 19);
        treeSet1.add(s1);
        treeSet1.add(s2);
        treeSet1.add(s3);
        treeSet1.add(s4);
        treeSet1.add(s5);//重复，不在添加
        System.out.println("元素个数："+treeSet1.size());//元素个数：4
        System.out.println(treeSet1);//[Student{name='张三', age=16}, Student{name='李四', age=17}, Student{name='王五', age=18}, Student{name='王五', age=19}]

        //2.删除元素
        //treeSet1.remove(s1);
        treeSet1.remove(new Student("张三", 16));
        System.out.println("元素个数："+treeSet1.size());//元素个数：3
        System.out.println(treeSet1);//[Student{name='李四', age=17}, Student{name='王五', age=18}, Student{name='王五', age=19}]

        //3.遍历
          //1.使用增强for
        for (Student s:
             treeSet1) {
            System.out.println(s);
        }

          //2.使用迭代器
        Iterator<Student> iterator1 = treeSet1.iterator();
        while (iterator1.hasNext()){
            System.out.println(iterator1.next());
        }

        //4.判断
        System.out.println(treeSet1.contains(s2));//true
        System.out.println(treeSet1.isEmpty());//false

        System.out.println("=========================");
        //Comparator接口:实现定制比较
        TreeSet<Student> treeSet2 = new TreeSet<>(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                int n1 = o1.getAge() - o2.getAge();
                int n2 = o1.getName().compareTo(o2.getName());
                return n1==0?n2:n1;
            }
        });
        Student s8 = new Student("张三", 15);
        Student s9 = new Student("李四", 17);
        Student s10 = new Student("王五", 18);
        treeSet2.add(s8);
        treeSet2.add(s9);
        treeSet2.add(s10);
        System.out.println("元素个数："+treeSet2.size());//元素个数：4
        System.out.println(treeSet2);//[Student{name='张三', age=16}, Student{name='李四', age=17}, Student{name='王五', age=18}, Student{name='王五', age=19}]

        //Comparator接口的应用：使用TreeSet集合实现字符串按照长度进行排序

        //创建集合，并指定比较规则
        TreeSet<String> treeSet3 = new TreeSet<>(new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                int n1 = o1.length() - o2.length();
                int n2 = o1.compareTo(o2);
                return n1==0?n2:n1;
            }
        });
        treeSet3.add("hubei");
        treeSet3.add("beijing");
        treeSet3.add("shanghai");
        treeSet3.add("tianjin");
        treeSet3.add("hunan");
        treeSet3.add("shandong");
        System.out.println(treeSet3);//[hubei, hunan, beijing, tianjin, shandong, shanghai]

    }

}

package edu.wtbu;

import java.util.Objects;

public class Student implements Comparable<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);
//    }

    //先按照姓名比，再按照年龄比
    @Override
    public int compareTo(Student o) {
        int n1 = this.getName().compareTo(o.getName());
        int n2 = this.age - o.getAge();
        return n1==0?n2:n1;
    }
}