Collection And Collections Framework In Java

Collection:-

• A group of individual objects as a single entry is called Collection.

Collection Framework:

• It defined several Classes & Interfaces, which can be used to represent a group of objects as a single entity.

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9-Key interfaces of Collections Framework are below:-

1. Collection (Interface):

• If we want to represent a group of individual objects as a single entity then we should go for collection.
• In general collection interface is considered as root interface of Collection Framework.
• Collection Interface defines the most common methods which can be applicable for any collection object.

 

Collection Vs Collections:

• Collection is an interface, can be used to represent a group of individual objects as a single entity where as
• Collections is a Utility Class, present in java, util package, to define several utility methods for collections.

2. List (Interface):

• It is the child Interface of collection.
• If we want to represent a group of individual objects where insertion order is preserved & duplicates are allowed. Then we should go for list.
• Vector & Stack classed are re-engineered in 1.2 version to fit into collection framework.

3. Set (Interface):

• It is the child interface of collection.
• If we want to represent a group of individual objects where “duplicated are not allowed & insertion order is not preserved”. Then we should go for “Set”.

 

4. Sorted Set (I):

• It is the child interface of Set.
• If we want to represent a group of individual objects according to some sorting order. Then we should go for Sorted Set.

5. Navigable Set (I):

• It is the child interface of Sorted Set to provide several methods for Navigation purposes,
• It is introduced in 1.6 version.

 

6. Queue (I):

• It is the child Interface of collection.
• If we want to represent a group of individual objects, prior to processing. Then we should go for Queue.

Note:

• All the above interfaces (Collection, List, Set, Sorted Set, Navigable Set, Queue) meant for representing a group of individual objects.
• If we want to represent a group of object as Key-value pairs then we should go for ‘Map’.

7. Map (I):

• If we want to represent a group of objects as Key-value pairs. Then we should go for Map.
• Both key & value are objects only.
• Duplicate keys are not allowed. But values can be duplicated.

Note:

• Map is not child interface of collection.

8. Sorted Map (I):

• If we want to represent a group of objects as Key value pairs according to some sorting order. Then we should go for Sorted Map.
• Sorting should be done only based on Keys, but not based on values.
• Sorted Map is child interface of Map.

9. Navigable Map (I):

• It is the child interface of Sorted Map & define several methods for Navigation purposes.
• In the collection framework, following are Legacy characters :

1. Enumeration (I)
2. Dictionary (ABC)

• Vector

1. Stack
2. Hash table
3. Propertied

Collection frame work:

Collection (I):

• If we want to represent a group of individual objects as a single entity then we should go for collection.
• Collection Interface defines the most common methods which can be applied for any collection object.
• Following is the list of methods present in collection interface:

1. Boolean add (object O)
2. Boolean add All (collection C)

• Boolean remove (object O)

1. Boolean remove All (collection C)
2. Boolean retain All (collection C)

• To remove all objects except those present in collection

1. Void Clear()

• Boolean isEmpty()
• Int Size()

1. Boolean contains (object O)
2. Boolean contains All (collection C)
3. Object[] to Array()

• Iterator iterator()

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