Difference between Collections and Collection in java with example program

In Java, "Collection" refers to the interface that defines the basic properties and behaviors of a collection, while "Collections" is a utility class that provides static methods for working with collections.

The Collection interface is part of the Java Collections Framework and it is a root interface for all the collections. It defines the basic properties and behaviors that all collections should have, such as adding and removing elements, checking the size of the collection, and so on.

It includes List, Set and Queue interfaces.

On the other hand, the Collections class is a utility class that provides various static methods for working with collections, such as sorting, reversing, and searching. It also provides methods for creating unmodifiable collections, which are collections that cannot be modified after they are created.

Here are some examples of how we can use the Collections class:

To sort a List:

List<Integer> myList = new ArrayList<>();

myList.add(3);

myList.add(1);

myList.add(2);

Collections.sort(myList);

To reverse an array:

Collections.reverse(myList);

To create an unmodifiable collection:

List<Integer> unmodifiableList = Collections.unmodifiableList(myList);

It's worth noting that, the Collections class only provides static methods, it does not provide any instance methods. So, you can't create an object of the Collections class.

• Famous java interview question: difference between collections and collection in java
• Major difference between Collection and Collections is Collection is an interface and Collections is a class. 
• Both are belongs to java.util package
• Collection is base interface for list set and queue.
• Collections is a class and it is called utility class.
• Collections utility class contains some predefined methods so that we can use while working with Collection type of classes(treeset, arraylist, linkedlist etc.)
• Collection is base interface for List , Set and Queue.

Collection vs Collections

1. public interface Collection<E> 
2. extends Iterable<E>

1. public class Collections
2. extends Object

• Collections utility class contains static utility methods so that we can use those methods by using class name without creating object of Collections class object
• Lest see some methods of Collections class.

1. addAll: public static <T> boolean addAll(Collection<? super T> c,T... elements)
2. reverseOrder: public static <T> Comparator<T> reverseOrder()
3. shuffle: public static void shuffle(List<?> list)
4. sort:public static <T extends Comparable<? super T>> void sort(List<T> list)

How to Relate Collection and Collections

• ArrayList is a Collection type of class means it is implementing Collection interface internally
• Now lets see a java example program to sort ArrayList of elements using Collections.sort() method.

1. public class ArrayList<E>
2. extends AbstractList<E>
3. implements List<E>, RandomAccess, Cloneable, Serializable

1.Basic Java example program to sort arraylist of integers using Collections.sort() method

1. package com.javasortarraylistofobjects;
2.  
3. import java.util.ArrayList;
4. import java.util.Collections;
5. import java.util.Iterator;
6.  
7. public class SortArrayListExample{
8.  
9. public static void main(String[] args) {
10.   
11. //create an ArrayList object
12.  ArrayList<Integer> arrayList = new ArrayList<Integer>();
13.        
14.  //Add elements to Arraylist
15. arrayList.add(10);
16. arrayList.add(7);
17. arrayList.add(11);
18. arrayList.add(4);
19. arrayList.add(9);
20. arrayList.add(6);
21. arrayList.add(2);
22. arrayList.add(8);
23. arrayList.add(5);
24. arrayList.add(1);
25.         
26.         
27.  System.out.println("Before sorting ArrayList ...");
28.  Iterator itr=arrayList.iterator();
29.         
30. while (itr.hasNext()) {
31.  
32. System.out.println(itr.next());
33.      
34. }
35.  
36.        
37.  /*
38.  To sort an ArrayList object, use Collection.sort method. This is a
39.   static method. It sorts an ArrayList object's elements into ascending order.
40. */
41.   Collections.sort(arrayList);
42.      
43.   System.out.println("After sorting ArrayList ...");
44.        
45.     
46.         
47. Iterator itr1=arrayList.iterator();
48.         
49. while (itr1.hasNext()) {
50. 
    
51. System.out.println(itr1.next());
52.             
53. }
54.     
55.   
56. }
57. }
     

Output:

1. Before sorting ArrayList ...
2. 10
3. 7
4. 11
5. 4
6. 9
7. 6
8. 2
9. 8
10. 5
11. 1
12. After sorting ArrayList ...
13. 1
14. 2
15. 4
16. 5
17. 6
18. 7
19. 8
20. 9
21. 10
22. 11