Comparable and Comparator

Comparable Interface

• Comparable Interface is meant for default natural Sorting order.

• It is present in Java.lang package.

• it is Contains Only one method Compare To().

• Compare To() method is responsible to sort the elements.

  You define the natural ordering for your objects by implementing the Comparable’s compareTo(T o) method in your custom objects. For example, if we want to compare the Person object based on the first name we’ll implement the Comparable interface .
  

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

public class ComparatorExample {
  public static void main(String[] args) {
    ArrayList  al  = new ArrayList();
    al.add("jai");
    al.add("vijay");
    al.add("maddy");
    al.add("ajai");
    al.add("don");
    Collections.sort();
    System.out.println(al);
  }
}

Comparator Interface

• Comparator Interface is meant for Customized Sorting Order.

• It is present in Java.util.

• It contains two method Compare() method and equals().

• Compare()method is responsible to sort the elements.

  If we want to define a total ordering on an object that has no natural ordering or if we want to override the natural ordering then we leverage the Comparator interface to do so. For example, if we want to override the natural ordering of Person objects and compare the Person object based on the age we’ll implement the Comparator interface
  

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

public class ComparatorExample implements Comparator <String>{
  public static void main(String[] args) {
    ArrayList  al  = new ArrayList();
    al.add("jai");
    al.add("vijay");
    al.add("maddy");
    al.add("ajai");
    al.add("don");
    Collections.sort(al,new ComparatorExample());
    System.out.println(al);
  }

  @Override
  public int compare(String o2, String o1) {
    return o2.compareTo(o1);
  }
}