Java のsort とComparator のサンプル

SortSample.java

package sortsample;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortSample {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        /*Arrays.sort 昇順
         http://docs.oracle.com/javase/jp/8/docs/api/java/util/Arrays.html#sort-int:A-
         */
        {
            int array[] = {3, 2, 1, 5, 4};

            Arrays.sort(array);
            System.out.println(Arrays.toString(array));
        }

        /*Arrays.sort Comparator 
         http://docs.oracle.com/javase/jp/8/docs/api/java/util/Arrays.html#sort-T:A-java.util.Comparator-
         */
        {
            System.out.println("Arrays.sort(,Comparator)");
            Integer array[] = {3, 2, 1, 5, 4};

            Arrays.sort(array, Comparator.naturalOrder());
            System.out.println(Arrays.toString(array));

            Arrays.sort(array, Comparator.reverseOrder());
            System.out.println(Arrays.toString(array));
        }

        /*Collections.sort
         http://docs.oracle.com/javase/jp/8/docs/api/java/util/Collections.html#sort-java.util.List-
         */
        {
            System.out.println("Collections sort:");
            List<Integer> list = new ArrayList<Integer>();
            Collections.addAll(list, 3, 2, 1, 4, 5);

            Collections.sort(list);
            System.out.println(list.toString());
        }

        /*
         Collections.sort(,Comparator)
         */
        {
            System.out.println("Collections.sort(,Comparator)");
            List<Integer> list = new ArrayList<Integer>();
            Collections.addAll(list, 3, 2, 1, 4, 5);

            list.sort(Comparator.naturalOrder());
            System.out.println(list.toString());

            Collections.sort(list, Comparator.reverseOrder());
            System.out.println(list.toString());
        }

        /*
         stream.sorted
         http://docs.oracle.com/javase/jp/8/docs/api/java/util/stream/Stream.html#sorted--
         */
        {
            System.out.println("stream sorted");
            int array[] = {3, 2, 1, 5, 4};

            System.out.println(Arrays.toString(Arrays.stream(array).sorted().toArray()));
        }

        /*
         stream.sorted(Comparator)
         http://docs.oracle.com/javase/jp/8/docs/api/java/util/stream/Stream.html#sorted-java.util.Comparator-
         */
        {
            System.out.println("stream.sorted(Comparator)");
            Integer array[] = {3, 2, 1, 5, 4};

            System.out.println(Arrays.toString(Arrays.stream(array).sorted(Comparator.naturalOrder()).toArray()));
            System.out.println(Arrays.toString(Arrays.stream(array).sorted(Comparator.reverseOrder()).toArray()));
        }

        /*
         独自オブジェクトの配列 sort
         */
        {
            System.out.println("独自オブジェクト");
            Person people[] = {
                new Person("Sato", 20),
                new Person("Tanaka", 15),
                new Person("Suzuki", 35),
                new Person("Yamamoto", 40),
                new Person("Koyama", 10)
            };

            Arrays.sort(people, Comparator.comparing(Person::getAge));
            System.out.println(Arrays.toString(people));

            Arrays.sort(people, Comparator.comparing(Person::getAge).reversed());
            System.out.println(Arrays.toString(people));
        }

        /*
         独自オブジェクトの配列 stream.sorted
         */
        {
            System.out.println("独自オブジェクト stream.sorted");
            Person people[] = {
                new Person("Sato", 20),
                new Person("Tanaka", 15),
                new Person("Suzuki", 35),
                new Person("Yamamoto", 40),
                new Person("Koyama", 10)
            };

            System.out.println("age naturalorder:");
            System.out.println(
                    Arrays.toString(Arrays.stream(people).sorted(Comparator.comparing(Person::getAge)).toArray())
            );
            
            System.out.println("age reverseorder:");
            System.out.println(
                    Arrays.toString(Arrays.stream(people).sorted(Comparator.comparing(Person::getAge).reversed()).toArray())
            );

            System.out.println("name naturalorder:");
            System.out.println(
                    Arrays.toString(Arrays.stream(people).sorted(Comparator.comparing(Person::getName)).toArray())
            );
            System.out.println("name reverseorder:");
            System.out.println(
                    Arrays.toString(Arrays.stream(people).sorted(Comparator.comparing(Person::getName).reversed()).toArray())
            );
        }

    }

}

class Person {

    private String name_;
    private int age_;

    public Person(String name, int age) {
        this.name_ = name;
        this.age_ = age;
    }

    public String getName() {
        return this.name_;
    }

    public int getAge() {
        return this.age_;
    }

    @Override
    public String toString() {
        return this.name_ + ", " + this.age_;
    }
}