[Java](Collections) - 정렬

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class test7 {

    public static void main(String[] args) throws IOException {

        /////////////////////////////////////////////////////////////
        // comparable
        ArrayList<Student> stlist = new ArrayList<Student>();
        stlist.add(new Student("test1", 10));
        stlist.add(new Student("test2", 9));
        stlist.add(new Student("test3", 8));
        stlist.add(new Student("test4", 7));

        Collections.sort(stlist);

        for (Student s : stlist) {
            System.out.println(s.age);
        }

        /////////////////////////////////////////////////////////////
        // comparator
        ArrayList<Students> stslist = new ArrayList<Students>();
        stslist.add(new Students("test1", 10));
        stslist.add(new Students("test2", 9));
        stslist.add(new Students("test3", 8));
        stslist.add(new Students("test4", 7));

        Collections.sort(stslist, new Comparator<Students>() {

            @Override
            public int compare(Students o1, Students o2) {
                if (o1.age < o2.age) {
                    return -1;
                } else if (o1.age > o2.age) {
                    return 1;
                }
                return 0;
            }
        });

        for (Students s : stslist) {
            System.out.println(s.age);
        }

    }
}

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

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public int compareTo(Student o) {
        if (this.age < o.age) {
            return -1;
        } else if (this.age > o.age) {
            return 1;
        }
        return 0;
    }
}

class Students {
    public String name;
    public int age;

    public Students(String name, int age) {
        this.name = name;
        this.age = age;
    }
}