在学习HashSet和TreeSet过程碰到这么个情况，同样的代码形式在HashSet类中运行正常，但是换成TreeSet类后提示ClassCastException: hashset_.Employee1 cannot be cast to java.。
因为初学java，也搞不懂两类之间的应用环境及相同方法的差异性。请查看下面一段代码，运行正常，但是修改成TreeSet类后就不行，请大家不吝赐教！
案例说明：旨在验证在HashSet类中可以按照某种设定，禁止添加重复元素。这里是设定员工（自定义Employee类）的姓名和生日（自定义类）分别相同的情况下，视为同一员工，禁止重复添加。

import java.util.HashSet;
import java.util.Objects;

@SuppressWarnings({"all"})
public class HashSet2 {
    public static void main(String[] args) {
        HashSet hashSet = new HashSet();
        hashSet.add(new Employee("tom",3000,new MyDate(1995,12,7)));
        hashSet.add(new Employee("jack",2400,new MyDate(1998,17,17)));
        hashSet.add(new Employee("tom",3000,new MyDate(1995,12,7)));
        hashSet.add(new Employee("marry",2000,new MyDate(2002,8,20)));
        System.out.println(hashSet);
    }
}

class Employee{
    private String name;
    private double sal;
    private MyDate birthday;

    public Employee(String name, double sal, MyDate birthday) {
        this.name = name;
        this.sal = sal;
        this.birthday = birthday;
    }

    public String getName() {
        return name;
    }

    public double getSal() {
        return sal;
    }

    public MyDate getBirthday() {
        return birthday;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return Objects.equals(name, employee.name) && Objects.equals(birthday, employee.birthday);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, birthday);
    }

    @Override
    public String toString() {
        return  "name=" + name + "  sal=" + sal + "  birthday=" + birthday ;
    }
}

class MyDate{
    private int year;
    private int month;
    private int day;

    public MyDate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public int getMonth() {
        return month;
    }

    public int getDay() {
        return day;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyDate myDate = (MyDate) o;
        return year == myDate.year && month == myDate.month && day == myDate.day;
    }

    @Override
    public int hashCode() {
        return Objects.hash(year, month, day);
    }

    @Override
    public String toString() {
        return "MyDate{" +
                "year=" + year +
                ", month=" + month +
                ", day=" + day +
                '}';
    }
}

不用回了，今天刚继续学习了TreeSet，需要重写内部类方法Comparator()，刚学习这玩意，累死我了
import java.
import java.util.Objects;
import java.util.TreeSet;
@SuppressWarnings({"all"})
public class TreeSet1 {
    public static void main(String[] args) {
        TreeSet treeSet = new TreeSet(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                Employee e1 = (Employee) o1;
                Employee e2 = (Employee) o2;
                if((Objects.equals(e1.getName(), e2.getName())) && (Objects.equals(e1.getBirthday(), e2.getBirthday()))) {
                    return 0;
                } else {
                    return 1;
                }
            }
        });
        treeSet.add(new Employee("tom",3000,new MyDate(1995,12,7)));
        treeSet.add(new Employee("jacd",2400,new MyDate(1998,17,17)));
        treeSet.add(new Employee("tom",3000,new MyDate(1995,12,7)));
        treeSet.add(new Employee("marry",2000,new MyDate(2002,8,20)));
        System.out.println(treeSet);
    }
}

class Employee {
    private String name;
    private double sal;
    private MyDate birthday;

    public Employee(String name, double sal, MyDate birthday) {
        this.name = name;
        this.sal = sal;
        this.birthday = birthday;
    }

    public String getName() {
        return name;
    }

    public double getSal() {
        return sal;
    }

    public MyDate getBirthday() {
        return birthday;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return Objects.equals(name, employee.name) && Objects.equals(birthday, employee.birthday);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, birthday);
    }

    @Override
    public String toString() {
        return  "name=" + name + "  sal=" + sal + "  birthday=" + birthday ;
    }
}

class MyDate{
    private int year;
    private int month;
    private int day;

    public MyDate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public int getMonth() {
        return month;
    }

    public int getDay() {
        return day;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyDate myDate = (MyDate) o;
        return year == myDate.year && month == myDate.month && day == myDate.day;
    }

    @Override
    public int hashCode() {
        return Objects.hash(year, month, day);
    }

    @Override
    public String toString() {
        return "MyDate{" +
                "year=" + year +
                ", month=" + month +
                ", day=" + day +
                '}';
    }
}