Java Collections (Collection Framework)

Let’s discuss one of the main conceptĀ of Java, (i.e. Collections Framework),


  • What is and why collections ?
  • Core collection interfaces
  • Implementations
  • Algorithms
  • Custom Implementations
  • Inseparability

Let’s start in the topics in depth below,

What is a collection ?

  • A “collection” is an object–sometimes called a container– is simply an object that groups multiple elements into a single unit.
  • A Collections framework is a unified architecture fro representing and manipulating collections.
  • Collections are used to store, manipulate, retrieve and communicate aggregate data.
  • All collections framework contain the following:
    • Interfaces
    • implementations
    • Algorithms

Benefits of Collection Framework

  • Reduces programming effort
  • Increases program speed and quality
  • Allows interoperability among unrelated APIs
    • The collection interfaces are the vernacular by which APIs pass collections back and forth


  • Collection interfaces are abstract data types that represent collections
    • collection interfaces are in the form of java interfaces
  • Interfaces allow collections to be manipulated independently of the implementation details of their representation
    • Polymorphic behavior.

Types of Implementations

  • General-purpose implementations
  • Special-purpose implementations
  • Concurrent implementations
  • Wrapper implementations
  • Convenience implementations
  • Abstract implementations

Implementations are the data objects used to store collections, which implement the interfaces. Each of the general-purpose implementations provides all optional operations contained in its interface.

  • Java Collection framework also provides several special-purpose implementations for situations that require nonstandard performance, usage restrictions, or other unusual behavior.

General Purpose Implementaitons


Core Collection interfaces Hierarchy



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