TreeMap的使用

package edu.wtbu;

import java.util.Comparator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class Demo01 {
    public static void main(String[] args) {
        //新建集合
        TreeMap<Student, String> treeMap = new TreeMap<>(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                int n1=o1.getStuNo()-o2.getStuNo();
                return n1;
            }
        });

        //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);
        treeMap.put(s1,"湖北");
        treeMap.put(s2,"湖南");
        treeMap.put(s3,"北京");


        System.out.println("元素个数："+treeMap.size());//元素个数：3
        System.out.println(treeMap);//{Student{name='张三', stuNo=16}=湖北, Student{name='李四', stuNo=17}=湖南, Student{name='王五', stuNo=18}=北京}

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

        //3.遍历
          //1.使用KeySet
        Set<Student> keySet = treeMap.keySet();
        for (Student key:
                keySet) {
            System.out.println(key+"--------"+treeMap.get(key));
        }

          //2.使用EntrySet
        Set<Map.Entry<Student, String>> entrySet = treeMap.entrySet();
        for (Map.Entry<Student, String> key:
                entrySet) {
            System.out.println(key);
        }

        //4.判断
        System.out.println(treeMap.containsKey(s2));//true
        System.out.println(treeMap.isEmpty());//false
    }
}

package edu.wtbu;

import java.util.Objects;

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

    public Student() {
    }

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

    public String getName() {
        return name;
    }

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

    public int getStuNo() {
        return stuNo;
    }

    public void setStuNo(int stuNo) {
        this.stuNo = stuNo;
    }

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

//    @Override
//    public boolean equals(Object o) {
//        if (this == o) return true;
//        if (o == null || getClass() != o.getClass()) return false;
//        Student student = (Student) o;
//        return stuNo == student.stuNo && Objects.equals(name, student.name);
//    }
//
//    @Override
//    public int hashCode() {
//        return Objects.hash(name, stuNo);
//    }


}