Map的实现类：TreeMap

1.存储结构：红黑树

2.实现了SortedMap接口（是Map的子接口），可以对key自动排序。

3.实例代码：Student类和Demo03

如果出现类转换异常  参考【TreeSet（红黑树）】

package com.map;

import java.util.Objects;

public class Student implements Comparable<Student>{
    private String name;
    private int stuNo;

    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 int compareTo(Student o) {
        int n1 = this.getStuNo()-o.getStuNo();
        int n2 = this.name.compareTo(o.getName());
        return n1==0?n1:n2;
    }
}

package com.map;

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

/**
 * TreeMap集合的使用
 * 存储结构：红黑树
 */
public class Demo03 {
    public static void main(String[] args) {
        //创建集合
        TreeMap<Student, String> treeMap = new TreeMap<>();
        //创建学生对象
        Student s1 = new Student("小王", 100);
        Student s2 = new Student("小刘", 101);
        Student s3 = new Student("小方", 102);
        Student s4 = new Student("小舟", 103);
        //1添加数据
        treeMap.put(s1,"北京");
        treeMap.put(s2,"上海");
        treeMap.put(s3,"福建");
        treeMap.put(s4,"重庆");
        System.out.println("学生个数："+treeMap.size());
        System.out.println(treeMap);

        //2删除数据
        treeMap.remove(s1);
        System.out.println(treeMap);

        //3遍历数据
        System.out.println("--------keySet()-----------");
        Set<Student> set = treeMap.keySet();
        for(Student s : set){
            System.out.println(s);
        }
        System.out.println("--------entrySet()-----------");
        Set<Map.Entry<Student, String>> entries = treeMap.entrySet();
        for(Map.Entry<Student, String> entry : entries){
            System.out.println(entry.getKey()+" "+entry.getValue());
        }
    }
}

结果：