Colection & Collections

What do you think Collection & Collections are same?

Answer is No Collection & Collections are not same.

Here we discussed how Collection & Collections are Difference.

Collection

• Collection is Interface.
• If we want to represent a group of individual object as a single entity than, we should go for Collection.

Collections

• Collections is a class.
• Collections is an Utility class present in Java.util  package to define several methods for Collection Objects.
• For eg:- Sorting, Searching etc.

What is Collection Framework ?

• It contains several classes & interfaces which can be used to represent a group of individual object as a single entity.
• 9 Key Interface of Collection Framework.

1. Collection
2. List
3. Set
4. Sorted Set
5. Navigable Set
6. Queue
7. Map
8. Sorted Map
9. Navigable Map

1.Collection (Interface)

• If we want to represent a group of individual object as a single entity than we should go for Collection.
• Collection Interface defines the most common methods which are applicable for any collection.
• In general Collection Interface considered as Root Interface Collection Framework.
• There is no Concrete class which implements collection directly.

2. List (Interface)

• It is the Child Interface of Collection.
• If you want to represent a group of individual Objects as a Single entity where, Duplication are allowed & Insertion order must be preserved than we should go for List(Interface).
• Duplication are allowed.
• Insertion Order must be Preserved. 

3. Set (Interface)

• It is the Child Interface of Collection.
• If you want to represent a group of individual Objects as a Single entity where, Duplication are not allowed & Insertion Order not required than we should go for Set(Interface).
• Duplication are Not allowed.
• Insertion order Not required.

4. Sorted Set(Interface)

• It is the child Interface of Set(Interface).
• If you want to represent a group of individual object as a Single entity where, Duplication are Not allowed Object should be Inserted according to some Sorting order than we should go for Sorted Set.
• Duplication are Not allowed.
• Object should be Inserted (Insertion & Sorting Order) are allowed.

5. Navigable Set(Interface)

• It is the Child Interface of Sorted Set(Interface).
• It Contains several methods for Navigable purpose.

6. Queue(Interface)

• It is child Interface of Collection.
• If we want to represent a group of individual objects Prior to Processing than, we should go for Queue.
• Usually Queue follows FIFO(First In First Out) but based on Requirement we can implement our own Priority order also.
• For eg:- 
• Before Sending a Mail, all mail Id's we have to share in some data structure.
• In which order we added Mail Id's in the some order only mail should be delivered.

Note:-

• All the above Interface[Collection, List, Queue, Set, Sorted Set, Navigable Set] meant for representing a group of individual Objects.
• If we want to represent a group of object as Key-Value-Pair than, we should go for Map.

7.  Map(Interface)

• Map is Not Child interface of Collection.

• Represent as a Key-value-Pair.
• Both Key & Value are Object Only.
• Duplicate keys are Not allowed but values can be Duplicated.
• for eg:-
• 
  
  
  
  
  
  

8. Sorted Map(Interface)

• It is Child interface of Map.
• If we want to represent a group of Key-Value-Pairs according to some Sorting order of keys than, we should go for sorted Map.
• In sorted Map the Sorting should be based on Key but not based on  value.

9. Navigable Map(Interface)

• It is the Child Interface of Sorted Map.
• It defines several methods for Navigation purpose.

Note:- Following Legacy Character are present in Collection Framework.

• Enumeration(Interface)
• Dictionary(AC)
• Vector(Class
• HashTable(Class)
• Properties(Class)
• Stack(Interface)

What is the need of Cursor in Collection?

• A group of individual object, we want get these object one by one from the collection than we will go for Cursor concept.

Three type of Cursor are present in Collection.

• Enumeration(Interface)
• Iterator(Interface)
• ListIterator(Interface)

In Collection Two Utility Classes

• Araays
• Collections