What is the main difference between Collection and Collections in Java? [closed]

Answer 1

Collection is an Interface which can used to Represent a Group of Individual object as a single Entity.

Collections is an utility class to Define several Utility Methods for Collection object.

Answer 2

The Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection.

Answer 3

Collection is a interface and Collections is class in Java.util package

Answer 4

Collections is a utility class, meaning that it defines a set of methods that perform common, often re-used functions, such as sorting a list, rotating a list, finding the minimum value etc. And these common methods are defined under static scope.

Collection is an interface that is implemented by AbstractCollection which in turn is implemented by AbstractList, AbstractSet etc.

Also, Collections class has thirty-two convenience implementations of its collection interfaces, providing unmodifiable collections, synchronized collections. Nearly all of these implementations are exported via static factory methods in one noninstantiable class (java.util.Collections).

Reference: Effective Java

Answer 5

Collection, as its javadoc says is "The root interface in the collection hierarchy." This means that every single class implementing Collection in any form is part of the Java Collections Framework.

The Collections Framework is Java's native implementation of data structure classes (with implementation specific properties) which represent a group of objects which are somehow related to each other and thus can be called a collection.

Collections is merely an utility method class for doing certain operations, for example adding thread safety to your ArrayList instance by doing this:

List<MyObj> list = Collections.synchronizedList(new Arraylist<MyObj>());

The main difference in my opinion is that Collection is base interface which you may use in your code as a type for object (although I wouldn't directly recommend that) while Collections just provides useful operations for handling the collections.

Answer 6

As per Java Doc Collection is:

The root interface in the collection hierarchy. A collection represents a group of objects, known as its elements. Some collections allow duplicate elements and others do not. Some are ordered and others unordered. The JDK does not provide any direct implementations of this interface: it provides implementations of more specific subinterfaces like Set and List. This interface is typically used to pass collections around and manipulate them where maximum generality is desired.

Where as Collections is:

This class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection, and a few other odds and ends.