Comparator 와 Comparable

public interface Comparator {

  int compare(Object o1, Object o2);

  boolean equals(Object obj); // equals를 overriding 하라는 

}

 

public interface Comparable {

  int compareTo(Object o);

}  

 

Integer에 구현된 comparable

 

public final class Integer extends Number implements Comparable {

  public int compareTo(Integer anotherInteger){

    int v1 = this.value; // 나 자신

    int v2 = anotherInteger.value; // 받은 값

    return (v1 < v2 ? -1 : (v1==v2? 0:1)); 

  }

}

 

import java.util.*;

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

    String[] animal = {"cat", "Dog", "lion", "Eagle", "tiger", "duck","ael","Ant"};

    Arrays.sort(animal);
    System.out.println(Arrays.toString(animal));
    Arrays.sort(animal, String.CASE_INSENSITIVE_ORDER);
    System.out.println(Arrays.toString(animal));
//    Arrays.sort(animal, Comparator.reverseOrder());
    Arrays.sort(animal, (o1, o2)-> o2.compareTo(o1));
    System.out.println(Arrays.toString(animal));

    int[] intArr = {1, 2, 3, 4, 7, 0, -2, 4};

    Arrays.sort(intArr);
    System.out.println(Arrays.toString(intArr));

    ArrayList<Integer> intList = new ArrayList<>(List.of(1, 2, 3, 4, 7, 0, -2, 4));
    for (Integer i : intList) System.out.print(i+",");
    System.out.println();

    Collections.sort(intList);
    for (Integer i : intList) System.out.print(i+", ");
    System.out.println();
    intList.sort((o1, o2) -> o2.compareTo(o1));
    for (Integer i : intList) System.out.print(i+", ");
  }


//  private static class Descending implements Comparator<Object> {
//    @Override
//    public int compare(Object o1, Object o2) {
//      if (o1 instanceof Comparable && o2 instanceof Comparable) {
//        Comparable c1 = (Comparable) o1;
//        Comparable c2 = (Comparable) o2;
//        return c2.compareTo(c1);
//      }
//      return -1;
//    }
//  }
}