[JAVA]Comparable , Comparator

Java에서 정렬을 하기위해 두가지 object를 비교하기위해서는 

1. comparable 인터페이스 에서 정의한 compareTo() 메소드를 구현

2. comparator 구현

1. Comparable 구현

1-1. Student.java

public class Student implements Comparable{
    private int id;
    private String name;
    private int age;
    private String phone;
    private String email;
    
    public Student(int id,String name,int age,String phone,String email){
        this.setId(id);
        this.setName(name);
        this.setAge(age);
        this.setPhone(phone);
        this.setEmail(email);
    }
    @Override
    public int compareTo(Object o) {
        // TODO Auto-generated method stub
        int age1 = ((Student)o).getAge();
        int age_diff = this.getAge() - age1;
        return age_diff;
    }
 
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", phone=" + phone + ", email=" + email + "]";
    }
 
        /*getter setter*/
 
    .....
 
}

1-2. main

package AL;
 
import java.util.ArrayList;
import java.util.Collections;
 
public class Student_Main {
 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<Student> students = new ArrayList<>();
        students.add(new Student(1, "DeadDE", 27, "1111","111@naver.com"));
        students.add(new Student(2, "avo", 21, "1111","111@naver.com"));
        students.add(new Student(3, "Ronaldo", 35, "7777","ronaldo@naver.com"));
        students.add(new Student(4, "Messi", 30, "1010","messi_@naver.com"));
        
        Collections.sort(students);
        for(Student student:students){
            System.out.println(student);
        }
    }
 
}

결과>>

Student [id=2, name=avo, age=21, phone=1111, email=111@naver.com]

Student [id=1, name=DeadDE, age=27, phone=1111, email=111@naver.com]

Student [id=4, name=Messi, age=30, phone=1010, email=messi_@naver.com]

Student [id=3, name=Ronaldo, age=35, phone=7777, email=ronaldo@naver.com]

2. comparator 구현

2-1. Student.java

public class Student{
    private int id;
    private String name;
    private int age;
    private String phone;
    private String email;
    
    public Student(int id,String name,int age,String phone,String email){
        this.setId(id);
        this.setName(name);
        this.setAge(age);
        this.setPhone(phone);
        this.setEmail(email);
    }
    
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", phone=" + phone + ", email=" + email + "]";
    }
        /*getter setter*/
}

2-2. Student_name_Comparator.java

import java.util.Comparator;
public class Student_name_Comparator implements Comparator<Student>{
    @Override
    public int compare(Student o1, Student o2) {
        // TODO Auto-generated method stub
        String name1 = o1.getName();
        String name2 = o2.getName();
        int diff = name1.compareTo(name2);
        return diff;
    }
}

2-3. main

import java.util.ArrayList;
import java.util.Collections;
 
public class Student_Main {
 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<Student> students = new ArrayList<>();
        students.add(new Student(1, "DeadDE", 27, "1111","111@naver.com"));
        students.add(new Student(2, "avo", 21, "1111","111@naver.com"));
        students.add(new Student(3, "Ronaldo", 35, "7777","ronaldo@naver.com"));
        students.add(new Student(4, "Messi", 30, "1010","messi_@naver.com"));
        
        Collections.sort(students, new Student_name_Comparator());
        for(Student student : students){
            System.out.println(student);
        }
    }
 
}
 

Collections.sort(students, new Student_name_Comparator());

결과 >>

Student [id=1, name=DeadDE, age=27, phone=1111, email=111@naver.com]

Student [id=4, name=Messi, age=30, phone=1010, email=messi_@naver.com]

Student [id=3, name=Ronaldo, age=35, phone=7777, email=ronaldo@naver.com]

Student [id=2, name=avo, age=21, phone=1111, email=111@naver.com]