Java自用集合练习题：TreeSet的自然排序与定制排序

Posted 2021-10-14 王六六的IT日常

定义一个 Employee 类。
该类包含：private 成员变量 name,age,birthday，其中 birthday 为MyDate 类的对象；并为每一个属性定义 getter, setter 方法；并重写 toString 方法输出 name, age, birthday。

MyDate 类包含: private 成员变量 year,month,day；并为每一个属性定义 getter, setter 方法；

创建该类的 5 个对象，并把这些对象放入 TreeSet 集合中
分别按以下两种方式对集合中的元素进行排序，并遍历输出：
1). 使 Employee 实现 Comparable 接口，并按 name 排序
2). 创建 TreeSet 时传入 Comparator 对象，按生日日期的先后排序。

Employee.java

使 Employee 实现 Comparable 接口，并按 name 排序

package com.atguigu.exer1;
/*
 *
 * 该类包含：private 成员变量 name,age,birthday，其中 birthday 为MyDate 类的对象；
 * 并为每一个属性定义 getter, setter 方法；
 * 并重写 toString 方法输出 name, age, birthday
 * @author WanZi
 * @create 2021-09-24 11:45
 */
public class Employee implements Comparable{
    private String name;
    private int age;
    private MyDate birthday;

    public Employee() {
    }

    public Employee(String name, int age, MyDate birthday) {
        this.name = name;
        this.age = age;
        this.birthday = birthday;
    }

    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 MyDate getBirthday() {
        return birthday;
    }

    public void setBirthday(MyDate birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + '\\'' +
                ", age=" + age +
                ", birthday=" + birthday +
                '}';
    }

    @Override
    //按照姓名的顺序排
    public int compareTo(Object o) {
        if(o instanceof Employee){
            Employee e = (Employee)o;
            return this.name.compareTo(e.name);
        }
        throw new RuntimeException("传入的数据类型不一致");
    }
}

MyDate.java

package com.atguigu.exer1;

/**
 *
 * private 成员变量 year,month,day；并为每一个属性定义 getter, setter方法；
 * @author WanZi
 * @create 2021-09-24 11:48
 */
public class MyDate implements Comparable{
    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 MyDate() {

    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getMonth() {
        return month;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }

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

    @Override
    public int compareTo(Object o) {
        if(o instanceof MyDate){

            MyDate m = (MyDate)o;

            //比较年
            int minusYear = this.getYear() - m.getYear();
            if(minusYear != 0){
                return minusYear;
            }

            //比较月
            int minusMonth = this.getMonth() - m.getMonth();
            if(minusMonth != 0){
                return minusMonth;
            }

            //比较日
            return this.getDay()  - m.getDay();
        }
        throw new RuntimeException("传入的数据不一致！");

    }
}

EmployeeTest.java (测试)

package com.atguigu.exer1;

import org.junit.Test;

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

/**
 *
 * 创建该类的 5 个对象，并把这些对象放入 TreeSet 集合中
 * 
 * 分别按以下两种方式对集合中的元素进行排序，并遍历输出：
 * 1). 使 Employee 实现 Comparable 接口，并按 name 排序
 * 2). 创建 TreeSet 时传入 Comparator 对象，按生日日期的先后排序。
 *
 * @author WanZi
 * @create 2021-09-24 13:22
 */
public class EmployeeTest {

    //问题2：定制排序 按生日日期的先后排序。
    @Test
    public void test2(){
        TreeSet<Employee> set = new TreeSet<Employee>(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                if(o1 instanceof Employee && o2 instanceof Employee){
                    Employee e1 = (Employee)o1;
                    Employee e2 = (Employee)o2;

                    MyDate b1 = e1.getBirthday();
                    MyDate b2 = e2.getBirthday();

                    //方式一：
//                    //比较年
//                    int minusYear = b1.getYear() - b2.getYear();
//                    if(minusYear != 0){
//                        return minusYear;
//                    }
//
//                    //比较月
//                    int minusMonth = b1.getMonth() - b2.getMonth();
//                    if(minusMonth != 0){
//                        return minusMonth;
//                    }
//
//                    //比较日
//                    return b1.getDay()  - b2.getDay();

                    //方式二：
                    return b1.compareTo(b2);

                }
                throw new RuntimeException("传入的数据不一致！");
            }
        });

        //添加数据
        Employee e1 = new Employee("刘德华",55,new MyDate(1965,5,4));
        Employee e2 = new Employee("张学友",43,new MyDate(1987,5,4));
        Employee e3 = new Employee("郭富城",44,new MyDate(1987,5,9));
        Employee e4 = new Employee("黎明",51,new MyDate(1954,8,12));
        Employee e5 = new Employee("梁朝伟",21,new MyDate(1978,12,4));

        set.add(e1);
        set.add(e2);
        set.add(e3);
        set.add(e4);
        set.add(e5);

        //遍历
        Iterator<Employee> iterator = set.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next());
        }

    }

    //问题1： 按 name 排序 使用自然排序
    @Test
    public void test1(){
        TreeSet<Employee> set = new TreeSet<Employee>();

        Employee e1 = new Employee("刘德华",55,new MyDate(1965,5,4));
        Employee e2 = new Employee("张学友",43,new MyDate(1987,5,4));
        Employee e3 = new Employee("郭富城",44,new MyDate(1987,5,9));
        Employee e4 = new Employee("黎明",51,new MyDate(1954,8,12));
        Employee e5 = new Employee("梁朝伟",21,new MyDate(1978,12,4));

        set.add(e1);
        set.add(e2);
        set.add(e3);
        set.add(e4);
        set.add(e5);

        //遍历
       Iterator<Employee> iterator = set.iterator();
       while(iterator.hasNext()){
           System.out.println(iterator.next());
       }
    }
}