建一個員工類 繼承Comparaple 

public class Employee implements Comparable<Employee> {

	private String name;
	private int age;
	private double salary;

	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;
	}

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public Employee(String name, int age, double salary) {
		super();
		this.name = name;
		this.age = age;
		this.salary = salary;
	}

	public Employee() {
		super();
		// TODO Auto-generated constructor stub
	}

	@Override
	public int compareTo(Employee o) {// 那當前 員工物件和外來員工物件進行比較 (自然順序比較是小的在前大的在後)
		if (this.getAge() > o.getAge()) {
			return -1;// this-o小於0，表示this在前 o在後
		} else if (this.getAge() == o.getAge()) {

			if (this.getSalary() > o.getSalary()) {
				return -1;
			} else if (this.getSalary() == o.getSalary()) {
				if (this.getName().hashCode() > o.getName().hashCode()) {
					return -1;// 返回小於0的值，當前物件在前，外來物件在後
				} else if (this.getName().hashCode() == o.getName().hashCode()) {
					return 0;// 同一個物件
				} else {
					return 1;
				}
			} else {
				return 1;// 返回大於0的值，當前物件在後，外來物件在前
			}
		} else {
			return 1;// this-o大於0，表示this在後 o在前
		}

	}

}
 

測試類Demo

package com.zhiyou.wch3;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.TreeSet;

public class Demo {
	public static void main(String[] args) {

		TreeSet<Employee> treeSet = new TreeSet<>();
		Employee employee = new Employee("小明", 20, 2000);
		Employee employee1 = new Employee("小張", 27, 2000);
		Employee employee2 = new Employee("小紅", 30, 2000);
		Employee employee3 = new Employee("小李", 20, 2000);
		Employee employee4 = new Employee("小明", 20, 2000);
		Employee employee5 = new Employee("小明", 25, 2000);
		Employee employee6 = new Employee("小明", 20, 4000);
		treeSet.add(employee6);
		treeSet.add(employee5);
		treeSet.add(employee4);
		treeSet.add(employee3);
		treeSet.add(employee2);
		treeSet.add(employee1);
		treeSet.add(employee);
		Iterator<Employee> iterator = treeSet.iterator();
		while (iterator.hasNext()) {
			Employee emp = iterator.next();
			System.out.println(emp.getAge() + "\t" + emp.getSalary() + "\t" + emp.getName().hashCode());
		}

	}

}