» » » Difference between Collections and Collection in java with example program

  • 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


difference between collections and collection in java

  • 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. System.out.println(itr1.next());
  51.             
  52. }
  53.     
  54.   
  55. }
  56. }
     


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

Instance Of Java

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