About Comparator Interface

[Abimaran Kugathasan]

In K & B's book, it's said that....

..... you can use it to sort instances of any class. ...

My Question is : How it's possible?

(Can we compare by same fields of difference Class' instances)

Please Confirm? Thanks........

[Ankit Garg]

The statement implies that you can use Comparator to sort instances of classes that don't implement Comparable. If you implement the type safe Comparator i.e. Comparator<Type>, then your compareTo method won't get instances of different class anyways...

[Abimaran Kugathasan]

Ankit Garg write :

..... your compareTo method .....

.

Is that compare() method or compareTo() method in the Comparator interface? I think, compare()???

[Wouter Oet]

The Comparator interface contains the compare method
The Comparable interface contains the compareTo Method

[Abimaran Kugathasan]

Thanks Wouter Oet

[Wouter Oet]

You're welcome

[Neha Daga]

but the compare method in Comparator makes use of compareTo method to do the comparison. That's why Ankit said compareTo method.

[Abimaran Kugathasan]

Ok, Neha Daga.... Thanks....

BTW, Can you give me good example, ........

[Neha Daga]

read comparator from K&B all the examples make use of it.

[Wouter Oet]

Neha Daga wrote:but the compare method in Comparator makes use of compareTo method to do the comparison. That's why Ankit said compareTo method.

That totally depends on the implementation. If I write an implementation of Comparator then it doesn't need to a Comparable implementation:

class Person implements Comparable<Person>{
	int age;
	int numberOfChildren;
	
	public int compareTo(Person p)
	{
		return age-p.age;
	}
}

class ChildrenComparator implements Comparator<Person>
{
	public int compare(Person p1, Person p2)
	{
		return p1.numberOfChildren - p2.numberOfChildren;
	}
}    

Ankit was refering to a type safe implementation. Like he said: Comparator i.e. Comparator<Type>

class ChildrenComparator implements Comparator<Person>
{
	public int compare(Person p1, Person p2)
	{
		return p1.numberOfChildren - p2.numberOfChildren;
	}
} 
// Vs
class ChildrenComparator implements Comparator
{
	public int compare(Object p1, Object p2)
	{
		return ((Person)p1).numberOfChildren - ((Person)p2).numberOfChildren;
	}
}