compare() and compareTo()

i am not clear about the difference between the compare() method and compareTo(); method,

what arguments it ttakes?
as far as i studied i have not understood the point that
compareto()--- we must modify the class whose instance we want to sort!! what does this mean?

and compare()---- we build a class seperate from the class whose instatnce we want to sort.! what does this mean?

can please give a good example to implement them?will be very helpful in understanding!

You got it. Here's an example to clarify your confusion.

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

class Test {
	public static void main(String... args) {
		List<ComparableVehicle> l = new ArrayList<ComparableVehicle>();
		l.add(new ComparableVehicle(90.00)); 
		l.add(new ComparableVehicle(9.00));
		l.add(new ComparableVehicle(900.00));
		Collections.sort(l);
		System.out.println("Comparable Vehicles "+l);
		List<NonComparableVehicle> l2 = new ArrayList<NonComparableVehicle>();
		l2.add(new NonComparableVehicle(90.00)); 
		l2.add(new NonComparableVehicle(9.00));
		l2.add(new NonComparableVehicle(900.00));
		Collections.sort(l2, new VehicleComparator());
		System.out.println("Non-Comparable Vehicles w/ comparator "+l2);
	}
}
class ComparableVehicle implements Comparable<ComparableVehicle> {
	double price;
	ComparableVehicle(double price) {
		this.price = price;
	}
	public double getPrice() {
		return this.price;
	}
	public String toString() {
		return price+"";
	}
	public int compareTo(ComparableVehicle other) {
		return new Double(price).compareTo(other.getPrice());
	}
}
class NonComparableVehicle {
	double price;
	NonComparableVehicle(double price) {
		this.price = price;
	}
	public double getPrice() {
		return this.price;
	}
	public String toString() {
		return price+"";
	}
}
class VehicleComparator implements Comparator<NonComparableVehicle> {
	public int compare(NonComparableVehicle current, NonComparableVehicle other) {
		return new Double(current.getPrice()).compareTo(other.getPrice());
	}
}

Thanks a lot ... nice exxample!

thus what i understood from the example is if we use comparator we need to do it with sepaerate class and if we use comparable we have to use in the same class which needs to be sorted? am i correct?

Then which is more advantageous?which should be used?

Very good example...indeed..!!

vijay umar wrote:thus what i understood from the example is if we use comparator we need to do it with sepaerate class and if we use comparable we have to use in the same class which needs to be sorted? am i correct?
Then which is more advantageous?which should be used?

Using Comparator<V> gives you more flexibility (i.e: ability to sort the objects of the same class in any number of ways you want).