When should a class be Comparable and/or Comparato

Question

I have seen classes which implement both Comparable and Comparator. What does this mean? Why would I use one over the other?

Answer 1

java.lang.Comparable

1. To implement Comparable interface, class must implement a single method compareTo()

   int a.compareTo(b)

2. You must modify the class whose instance you want to sort. So that only one sort sequence can be created per class.

java.util.Comparator

1. To implement Comparator interface, class must implement a single method compare()

   int compare (a,b)

2. You build a class separate from class whose instance you want to sort. So that multiple sort sequence can be created per class.

Answer 2

If you see then logical difference between these two is Comparator in Java compare two objects provided to him, while Comparable interface compares "this" reference with the object specified.

Comparable in Java is used to implement natural ordering of object. In Java API String, Date and wrapper classes implement Comparable interface.

If any class implement Comparable interface in Java then collection of that object either List or Array can be sorted automatically by using Collections.sort() or Array.sort() method and object will be sorted based on there natural order defined by compareTo method.

Objects which implement Comparable in Java can be used as keys in a sorted map or elements in a sorted set for example TreeSet, without specifying any Comparator.

Answer 3

Implementing Comparable means "I can compare myself with another object." This is typically useful when there's a single natural default comparison.

Implementing Comparator means "I can compare two other objects." This is typically useful when there are multiple ways of comparing two instances of a type - e.g. you could compare people by age, name etc.

Answer 4

Comparable is for objects with a natural ordering. The object itself knows how it is to be ordered.
Comparator is for objects without a natural ordering or when you wish to use a different ordering.

Answer 5

here are few differences between Comparator and Comparable I found on web :

1. If you see then logical difference between these two is Comparator in Java compare two objects provided to him, while Comparable interface compares "this" reference with the object specified.

2. Comparable in Java is used to implement natural ordering of object. In Java API String, Date and wrapper classes implement Comparable interface.

3. If any class implement Comparable interface in Java then collection of that object either List or Array can be sorted automatically by using Collections.sort() or Array.sort() method and object will be sorted based on there natural order defined by CompareTo method.

4. Objects which implement Comparable in Java can be used as keys in a sorted map or elements in a sorted set for example TreeSet, without specifying any Comparator.

site:How to use Comparator and Comparable in Java? With example

Read more: How to use Comparator and Comparable in Java? With example

Answer 6

Comparable is for providing a default ordering on data objects, for example if the data objects have a natural order.

A Comparator represents the ordering itself for a specific use.