The Collection in Java is a framework that provides an architecture to store and manipulate a group of objects.
All the operations that you perform on data such as searching, sorting, insertion, manipulation, deletion, etc. can be achieved by Java Collections.
Collection Framework defines several classes and interfaces to represent a group of objects as a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data.
Java Collections Framework - Full 3Hr Course
What is a Collections Framework?
A collections framework is a unified architecture for representing and manipulating collections.
All collections frameworks contain the following:
- Interfaces: These are abstract data types that represent collections. Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages, interfaces generally form a hierarchy.
- Implementations: These are the concrete implementations of the collection interfaces. In essence, they are reusable data structures.
- Algorithms: These are the methods that perform useful computations, such as searching and sorting, on objects that implement collection interfaces. The algorithms are said to be polymorphic: that is, the same method can be used on many different implementations of the appropriate collection interface. In essence, algorithms are reusable functionality.
Benefits of the Java Collections Framework
The Java Collections Framework provides the following benefits:
- Reduces programming effort by providing data structures and algorithms so you don't have to write them yourself.
- Increases performance by providing high-performance implementations of data structures and algorithms. Because the various implementations of each interface are interchangeable, programs can be tuned by switching implementations.
- Provides interoperability between unrelated APIs by establishing a common language to pass collections back and forth.
- Reduces the effort required to learn APIs by requiring you to learn multiple ad hoc collection APIs.
- Reduces the effort required to design and implement APIs by not requiring you to produce ad hoc collections APIs.
- Fosters software reuse by providing a standard interface for collections and algorithms with which to manipulate them.
Hierarchy of Collection Framework
Let us see the hierarchy of the Collection framework. The java.util package contains all the classes and interfaces for the Collection framework.
The collection interfaces are divided into two groups:
The most basic interface, java.util.Collection.
The other collection interfaces are based on java.util.Map and are not true collections:
The collection interfaces are divided into two groups:
The most basic interface, java.util.Collection.
Collection Interfaces
The collection interfaces are divided into two groups. The most basic interface, java.util.Collection, has the following descendants:
- java.util.Collection
- java.util.List
- java.util.Set
- java.util.SortedSet
- java.util.NavigableSet
- java.util.Queue
- java.util.concurrent.BlockingQueue
- java.util.concurrent.TransferQueue
- java.util.Deque
- java.util.concurrent.BlockingDeque
The other collection interfaces are based on java.util.Map and are not true collections. However, these interfaces contain collection-view operations, which enable them to be manipulated as collections.
Interfaces related to Map:
- java.util.Map
- java.util.SortedMap
- java.util.NavigableMap
- java.util.concurrent.ConcurrentMap
- java.util.concurrent.ConcurrentNavigableMap
Collection Implementations
The general-purpose collection interface implementations are summarized in the following table:
The AbstractCollection, AbstractSet, AbstractList, AbstractSequentialList and AbstractMapclasses provide basic implementations of the core collection interfaces, to minimize the effort required to implement them.
The API documentation for these classes describes precisely how each method is implemented so the implementer knows which methods must be overridden, given the performance of the basic operations of a specific implementation.
Commonly used implementations
The Java Collections Framework provides several general-purpose implementations of the core interfaces:
- For the Set interface, HashSet is the most commonly used implementation.
- For the List interface, ArrayList is the most commonly used implementation.
- For the Map interface, HashMap is the most commonly used implementation.
- For the Queue interface, LinkedList is the most commonly used implementation.
- For the Deque interface, ArrayDeque is the most commonly used implementation.
Interfaces
- Collections Framework - The Collection Interface
- Collections Framework - The Set Interface
- Collections Framework - The SortedSet Interface
- Collections Framework - The List Interface
- Collections Framework - The Queue Interface
- Collections Framework - The Deque Interface
- Collections Framework - The Map Interface
- Collections Framework - The SortedMap Interface
List Implementations
General-Purpose List Implementations:
Special-Purpose List Implementations:
Set Implementations
General-Purpose Set Implementations:
Special-Purpose Set Implementations:
Map Implementations
General-purpose Map Implementations:
- Collections Framework - HashMap Class
- Collections Framework - LinkedHashMap Class
- Collections Framework - TreeMap class
Special-Purpose Map Implementations:
Sorting
Aggregate Operations(Streams)
Collections Helper/Utility Classes
- java.util.Collections Class API Guide(Development)
- 18 Useful Collections Utility Methods (Development)
- Java CollectionUtils Class(Development)
Convert Collections Examples
- Conversion Between Array and Set in Java
- Conversion Between Array and List in Java
- Java Convert Map to Set Example
- Java Convert Map to List Example
- Java Convert Map to Array Example
- Convert a Map to an Array, List, and Set in Java
- Java 8 Convert List to Map Example
- Java 8 - Merging Two Maps Example
- Java Convert Array to String [Snippet]
Collections Examples
- Different Ways to Iterate over List, Set, and Map in Java
- Java Comparator Interface Example
- Java Comparable Interface Example
- Java IdentityHashMap Example
- Java WeakHashMap Example
- Java EnumMap Example
- Java CopyOnWriteArraySet Example
- Java EnumSet Class Example
- Guide to Java 8 forEach Method
- Different Ways to Iterate over a List in Java [Snippet]
- Different Ways to Iterate over a Set in Java [Snippet]
- Different Ways to Iterate over a Map in Java [Snippet]
- Iterate over TreeSet in Java Example
- Iterate over LinkedHashSet in Java Example
- Remove First and Last Elements of LinkedList in Java
- Iterate over LinkedList using an Iterator in Java
- Search an Element in an ArrayList in Java
- Iterate over ArrayList using Iterator in Java
- Remove Element from HashSet in Java
- Iterating over a HashSet using Iterator
Collections Differences
- Collections vs Streams in Java
- Difference between Array vs ArrayList in Java
- Difference between LinkedList vs ArrayList in Java
- Difference between List and Set in Java Collection
- Difference between Stack and Queue Data Structure in Java
- Difference between HashMap and HashSet in Java
- Difference between TreeSet, LinkedHashSet, and HashSet in Java with Example
- Difference between EnumMap and HashMap in Java
- Difference between HashMap and HashSet in Java
- Difference between ArrayList and Vector in Java
- Difference between HashMap, LinkedHashMap, and TreeMap in Java
- Difference between PriorityQueue and TreeSet in Java?
- What is the difference between Enumeration and Iterator in Java?
- What is the difference between HashMap and Hashtable in Java?
- Difference between fail-fast Iterator vs fail-safe Iterator in Java
YouTube Video Series - Java Collections Framework in Depth Series
- Java Collections Framework in Depth - 1 - Need for Collections Framework
- Java Collections Framework in Depth - 2 - Collections Framework Hierarchy
- Java Collections Framework in Depth - 3 - Collection Interface with Coding Example
- Java Collections Framework in Depth - 4 - List Interface with Coding Example
- Java Collections Framework in Depth - 5 - ArrayList Class Overview
- Java Collections Framework in Depth - 6 - Creating an ArrayList and Adding New Elements to It
- Java Collections Framework in Depth - 7 - Creating ArrayList from Another Collection
- Java Collections Framework in Depth - 8 - Accessing Elements from an ArrayList
- Java Collections Framework in Depth - 9 - Removing Elements from an ArrayList
- Java Collections Framework in Depth - 10 - Iterating Over an ArrayList (6 Ways)
- Java Collections Framework in Depth - 11 - ListIterator Interface with Coding Example
- Java Collections Framework in Depth - 12 - CopyOnWriteArrayList Class with Coding Example
- Java Collections Framework in Depth - 13 - LinkedList Overview | ArrayList vs LinkedList
- Java Collections Framework in Depth - 14 - Create LinkedList Example | add(), addFirst and addLast()
- Java Collections Framework in Depth - 15 - Retrieving Elements from a LinkedList
- Java Collections Framework in Depth - 16 - Removing Elements from a LinkedList
- Java Collections Framework in Depth - 18 - HashSet Class Overview | Key Points to Note
The complete youtube playlist at https://youtube.com/playlist?list=PLGRDMO4rOGcNpAJPtuuCOPXvI39Elxa-c
Best Practices and Interviews
- Java Collection Framework Best Practice (Best Practice)
- Difference between Array vs ArrayList in Java (interview)
- How does the Size of the ArrayList Increases Dynamically? (interview)
- How To Remove Duplicate Elements From ArrayList In Java? (interview)
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