Difference between Collections and Collection in java with example program

Core java Interview Questions java Collections interview Questions

• 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

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Difference between Collections and Collection in java with example program

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Oleh Kris Kimcil

Kris Kimcil 09.07 1 Komentar