Java Interview Questions: Understanding Collection vs Collections

1) Extends: Collection interface extends iterable interface.

public interface Collections 
extends Iterable

On the other hand, Collections class extends Object class.

public class Collections
extends Object

2) Static methods : Collection is an interface. Interface can contain static methods since java 8. Before java8, interface was not allowed to contain static methods. Interface can also contain abstract methods and default methods.
On the other hand, Collections class contains only static methods.

Image from Edureka | Collections tree

3) Type: Collection is a root-level interface in Java Collection Framework or collection hierarchy.
Collections is a utility class in java that contains only static methods that operate on or return collections.

1. Most of the java collections framework classes inherit from Collection interface.

2. Set, Queue and List are some of the main subinterfaces of Collection interface.

3. Map interface is also part of the Collections Framework. But it doesn't inherit Collection interface.

4. The jdk does not provide direct implementation of Collection interface. Although, it provides implementation of specific subinterfaces like Set, List and Queue.

5. HashSet, ArrayList, LinkedHashSet, Vector, PriorityQueue are some indirect implementations of Collection Interface.

6. Collections is a utility class in java which contains only static methods. Using this class methods you can search for a particular element in a collection. It also contains the methods to sort the collection.

1. Both are part of the Java Collections Framework.

2. Both are present in java.util package.

3. Both are added to jdk in java version 1.2

Please mention in the comments in case you have any doubts regarding the difference between Collection and Collections in java.