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A Collection is an in-memory data structure that stores elements. All elements must exist before being added and you can perform operations like search, sort, insert, update or delete. Examples: List, Set, Queue, ArrayList, LinkedList, HashSet, etc.

On the other hand, A Stream (introduced in Java 8) is used to process collections of objects. It represents a sequence of elements and allows you to chain methods to produce results without changing the original collection.

Example: Collections

Java

import java.io.*;
import java.util.*;

class GfG {

    public static void main(String[] args)
    {
        // Creating an instance of list
        List<String> companyList = new ArrayList<>();

        // Adding elements using add() method
        companyList.add("Google");
        companyList.add("Apple");
        companyList.add("Microsoft");

        // Now creating a comparator
        Comparator<String> com = (String o1, String o2) -> o1.compareTo(o2);

        // Sorting the list
        Collections.sort(companyList, com);

        // Iterating using for each loop
        for (String name : companyList) {
            System.out.println(name);
        }
    }
}

Output

Apple
Google
Microsoft

Example: Streams

Java

import java.io.*;
import java.util.*;

class GFG {

    public static void main(String[] args)
    {
        // Creating an empty Arraylist
        List<String> companyList = new ArrayList<>();

        // Adding elements to above ArrayList
        companyList.add("Google");
        companyList.add("Apple");
        companyList.add("Microsoft");

        // Sorting the list using sorted() method and  using for-each loop
        companyList.stream().sorted().forEach(
            System.out::println);
    }
}

Output

Apple
Google
Microsoft

Difference Between Streams and Collections

Streams	Collections
Do not store data, operate on source data (like Collections/Arrays).	Store and hold data in structures like List, Set or Map.
Use functional style (lambdas, method references).	Do not use functional interfaces directly.
Consumable once used, must be recreated to traverse again.	Reusable can be traversed multiple times.
Support sequential and parallel processing.	Mostly sequential, parallelism requires extra effort.
Belong to java.util.stream package.	Belong to java.util package (e.g., List, Set, Queue).
Not modifiable, cannot add or remove elements.	Modifiable, elements can be added or removed.
Internal iteration (handled by the Stream API).	External iteration (using loops/iterators).

Streams vs. Collections in Java

Difference Between Streams and Collections

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