• Sorting of objects based on natural order uses Comparable whereas if you sorting needs to be done on attributes of different objects, then use Comparator in Java

public class Car implements Comparable<Car>
{
	private String maker;
	private String color;

	public Car(String maker, String color)
	{
		this.maker = maker;
		this.color = color;
	}

	public int compareTo(Car c)
	{
		return maker.compareTo(c.maker);
	}

	public static void main(String args[])
	{
		Car c = new Car("Buick", "White");
		Car c2 = new Car("Honda", "Blue");

		System.out.println(c.compareTo(c2));

		if(c.compareTo(c2) < 0)
			System.out.println("Less than ...");
	}
}
			

import java.util.*;

public class Car implements Comparable<Car>
{
	private String maker;
	private String color;

	public Car(String maker, String color)
	{
		this.maker = maker;
		this.color = color;
	}

	public int compareTo(Car c)
	{
		//System.out.println(maker+" - "+c.maker+" "+maker.compareTo(c.maker));
		return maker.compareTo(c.maker);
	}

	public String toString()
	{
		return maker+": "+color;
	}

	public static void main(String args[])
	{
		PriorityQueue<Car> q = new PriorityQueue<Car>();

		q.add(new Car("Buick", "White"));
		q.add(new Car("Honda", "Blue"));
		q.add(new Car("Accord", "Blue"));
		q.add(new Car("Lincoln", "White"));

		System.out.println(q);

		//poll objects in the queue by priority
		for(int i = 0, len = q.size(); i < len; i++)
			System.out.println(q.poll());
	}
}
			

import java.util.*;

public class Car implements Comparable<Car>
{
	private String maker;
	private String color;

	public Car(String maker, String color)
	{
		this.maker = maker;
		this.color = color;
	}

	public int compareTo(Car c)
	{
		//System.out.println(maker+" - "+c.maker+" "+maker.compareTo(c.maker));
		return maker.compareTo(c.maker);
	}

	public String toString()
	{
		return maker+": "+color;
	}

	public static void main(String args[])
	{
		SortedSet<Car> s = new TreeSet<Car>();

		s.add(new Car("Buick", "White"));
		s.add(new Car("Honda", "Blue"));
		s.add(new Car("Accord", "Blue"));
		s.add(new Car("Lincoln", "White"));

		System.out.println(s);
	}
}
			

import java.util.*;

public class Car
{
	private String maker;
	private String color;

	public Car(String maker, String color)
	{
		this.maker = maker;
		this.color = color;
	}

	public String toString()
	{
		return maker+": "+color;
	}

	public String getMaker()
	{
		return maker;
	}

	public String getColor()
	{
		return color;
	}
}
			

import java.util.*;

public class CarComparator implements Comparator
{
	public int compare(Car c1, Car c2)
	{
		return (c1.getMaker().compareTo(c2.getMaker()));
	}
}
			

import java.util.*;

public class Main
{
	public static void main(String args[])
	{
		ArrayList<Car> l = new ArrayList<Car>();

		//add
		l.add(new Car("Buick", "White"));
		l.add(new Car("Honda", "Blue"));
		l.add(new Car("Lincoln", "White"));
		l.add(new Car("Accord", "Blue"));

		System.out.println(l);

		//sort by comparator
		Collections.sort(l, new CarComparator());

		System.out.println(l);
	}
}