Collection vs Collections: Difference Between Collection and Collections in Java

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In this article, we will discuss the difference between Collection and Collections in Java.

Java is well known for its comprehensive library, one of which is the Java Collections Framework. It includes interfaces and classes that are used to represent and manipulate collections of objects. Two terms that are often discussed when talking about this framework are Collection and Collections. They sound similar, but they are fundamentally different.

Collection - It is an Interface

The Collection is an interface in the Java Collections Framework. 

It defines the basic methods that all collections will have, such as add(), remove(), size(), isEmpty(), iterator(), etc. 

The Collection is essentially a group of individual objects represented as a single unit. 

It acts as the root interface in the collection hierarchy and is located in java.util package.

Collection is more of a concept for storing data, rather than a tool for manipulating data.

Collection Interface Example

The following example demonstrates the usage of important Collection interface methods:

import java.util.ArrayList;
import java.util.Collection;

public class CollectionDemo {

    public static void main(String[] args) {

        Collection < String > fruitCollection = new ArrayList < > ();
        fruitCollection.add("banana");
        fruitCollection.add("apple");
        fruitCollection.add("mango");
        System.out.println(fruitCollection);

        fruitCollection.remove("banana");
        System.out.println(fruitCollection);

        System.out.println(fruitCollection.contains("apple"));

        fruitCollection.forEach((element) -> {
            System.out.println(element);
        });

        fruitCollection.clear();

        System.out.println(fruitCollection);
    }
}

Output:

[banana, apple, mango]
[apple, mango]
true
apple
mango
[]

In the above example, we can clearly see that the Collection is an interface and we used it as a reference type:

        Collection <String> fruitCollection = new ArrayList<>();

Collections - It is a Utility Class

Collections is a utility class (final class) present in java.util package. 

It defines several utility methods like sort(), synchronizedList(), unmodifiableList(), reverse(), shuffle(), etc. These methods are used to operate and manipulate the data in Collection objects. 

Collections class methods throw a NullPointerException if the collections or class objects provided to them are null. 

This class contains static methods which operate on or return collections. 

Collections Utility Class Example

The following Java program demonstrates the usage of the Collections.sort() method, which is used to sort elements in a collection in ascending order, according to their natural ordering.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<String> list = new LinkedList<>();
        list.add("element 2");
        list.add("element 1");
        list.add("element 4");
        list.add("element 3");
        // Sorts the specified list into ascending order, according to
        // the natural ordering of its elements.
        Collections.sort(list);
        for (String str : list) {
            System.out.println("sort elements in ascending order  --" + str);
        }
    }
}

Output:

 sort elements in ascending order  --element 1
 sort elements in ascending order  --element 2
 sort elements in ascending order  --element 3
 sort elements in ascending order  --element 4

Learn more about Collections class: Java Collections Class (Utility Class)

Collection vs Collections - Cheat Sheet

Conclusion

So in summary, Collection is an interface that can be used to represent a group of objects as a single unit while Collections is a utility class in Java that contains various static methods to efficiently manipulate data in a collection.

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