What is a collection and collections in Java? One might often get confused about collection vs collections in the Java language. Are these two similar terms, or different in operation? The following information might give a more clear idea about them.
What Is Collection in Java?
- Collection in Java is simply known as an interface that is present in java.util.package.
- Collection is able to form the root or head of the hierarchy of interfaces in the java collection framework.
- Collection is used to group various objects into a single unit. It is quite similar to containers in the C++ interface. Some of the most essential methods of the Collection interface are add(), remove(), clear(), size(),contains() whereas sets, lists, maps, queues, deque, etc. are the sub-main interfaces of the collection framework in Java. However, interfaces also contain some default as well as abstract methods.
Declaration of Collection
public interface Collection<E> extends Iterable<E>
Need for Collection
- Collection interfaces are able to perform operations such as dealing with various objects by grouping them in an efficient manner. However, these objects might be similar or different from each other. Thus, the use of sub-interfaces such as sets, lists, maps, queues, and deque depends on the objects and their way of dealing with individual objects.
- Set is one of the most important subinterfaces in the collection that it doesn’t contain any duplicate elements or objects. The Set Interface can be found in the java.util package. Sets are usually unordered so that they do not return their elements in their collection. Many times, Java developers often forget that sets are unordered thus they might often face bugs in their code. Classes such as EnumSet, HashSet, LinkedHashSet, TreeSet and ConcurrentSkipListSet are some of the most essential set classes that can be implemented on the collection interface.
- List is one of the sub-interface in the collection and is also similar to Python Lists with some differences and used for ordered elements or objects in sorted form. Lists can have duplicate elements in the collection. A list’s elements are accessible with the help of its elements’ index or position. Also, lists can help us search for the element. The most commonly used list classes on the list interfaces are Vector, Stack, LinkedList, ArrayList, and CopyOnWriteArrayList.
- Stack and Queue are also sub-interfaces in the collection. The stack interface is implemented with the help of the usual LIFO (Last In First Out) data structure in that elements are pushed into one end of the stack. Later, those elements pop out from the same end of that stack.
- Map Interface is a subinterface in the collection, similar to the Dictionary data structure in the Python Language. Map interface is used to group and store data elements in key-value pairs where each key is unique and thus there are no duplicate keys. Its corresponding value is returned with the help of a key. Some of the most essential classes in the Map interface are HashMap, HashTable, EnumMap, TreeMap, IdentityHashMap, and WeakHashMap.
- Queue interface in collection depends on the queue data structure that implements a FIFO (First In First Out) method where elements are pushed to one end of the queue and can be popped out from the other end of the same queue.
What Are Collections in Java?
- Collections in Java is a utility class that is found in java.util.package that defines several.
- Collections class uses static methods for computations, also known as utility methods that are used to operate on the collection.
Declaration of Collections
public class Collections extends Object
Need for Collections
- Developers often find Collections classes operations easy and extremely convenient to perform the basic operations on elements as there is no more need to get into the details of any basic operations and can focus on the more important tasks.
- Collections class uses a particular method to search for a particular element in a collection. Thus, it is able to perform sorting operations on the elements of the Collection interface.
- Collections.binarySearch() is used to search for the desired element in a collection with the help of the popular Binary Search Algorithm.
- Collections.sort() is used to perform sorting operations on the specified Collection.
- Collections.max() is used to return the maximum element from a specified Collection.
- Collections.min() is used to return the minimum element from a specified Collection.
- Collections.reverse() is used to reverse the order of the elements present in the specified Collection.
- Collections.copy() function is used to copy one element from one collection to another collection.
Collection vs Collections in Java
- Collection is called interface in java whereas Collections is called a utility class in java and both of them can be found in java.util.package.
- Collection is used to represent a single unit with a group of individual objects whereas collections is used to operate on collection with several utility methods.
- Since java 8, collection is an interface with static as well as abstract and default methods whereas collections operate only with static methods.
Java Program to Demonstrate the Difference Between Collection and Collections
// Java program to demonstrate the difference
// between Collection and Collections
public static void main (String args)
// Creating an object of List<String>
List<String> arrlist = new ArrayList<String>();
// Adding elements to arrlist
// Printing the elements of arrlist
// before operations
System.out.println(“Elements of arrlist before the operations:”);
System.out.println(“Elements of arrlist after the operations:”);
// Adding all the specified elements
// to the specified collection
Collections.addAll(arrlist, “web”, “site”);
// Printing the arrlist after
// performing addAll() method
// Sorting all the elements of the
// specified collection according to
// default sorting order
// Printing the arrlist after
// performing sort() method
Elements of arrlist before the operations:
[geeks, for, geeks]
Elements of arrlist after the operations:
[geeks, for, geeks, web, site]
[for, geeks, geeks, site, web]
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