Collections in Java With Hierarchy

Collections in Java provide a way to store and manipulate groups of objects. Think of collections as containers that allow you to efficiently manage, organize, and manipulate data.

In Java, the Collections Framework is a set of interfaces and classes that provide reusable data structures.

Collection Hierarchy:

List Interface

    - Represents an ordered collection, allowing duplicate elements.

    - Key implementations include ArrayList and LinkedList.

    - Methods like add, remove, and get are common in List implementations.

ArrayList:

  - Implements the List interface and is backed by a dynamic array.

  - Provides fast random access and dynamic resizing.

  - Suitable for scenarios where frequent access and modification of elements are required.

LinkedList:

  - Also implements the List interface but is backed by a doubly-linked list.

  - Well-suited for scenarios where frequent insertion and deletion operations are common.

  - Supports sequential access and offers constant-time insertions and deletions.

Vector:

Similar to ArrayList, implements the List interface, and is synchronized.

Suitable when thread safety is essential but might incur performance overhead.

Stack:

A subclass of Vector, implements the List interface with additional methods.

Follows the Last In, First Out (LIFO) principle, commonly used in undo mechanisms.

Set Interface

    - Represents an unordered collection with no duplicate elements.

    - Key implementations include HashSet and TreeSet.

    - Useful when uniqueness and absence of order are essential.

HashSet:

  - Implements the Set interface and uses a hash table for storage.

  - Provides constant-time performance for basic operations like add, remove, and contains.

  - Does not guarantee order.

LinkedHashSet:

Extends HashSet, preserving insertion order.

Ideal when the order of elements needs to be maintained.

TreeSet:

  - Also implements the Set interface but maintains elements in sorted order.

  - Utilizes a red-black tree data structure for storage.

  - Useful when a sorted set of elements is required.

Queue Interface

    - Extends Collection and represents a collection designed for holding elements prior to processing.

    - Key implementations include LinkedList and PriorityQueue.

    - Supports operations like enqueue and dequeue.

PriorityQueue:

  - Implements the Queue interface and represents a priority queue.

  - Elements are ordered based on their natural ordering or a provided comparator.

  - Useful in scenarios where elements need to be processed based on priority.

Deque Interface:

Represents a double-ended queue, allowing insertion and removal from both ends.

Implementations include ArrayDeque and LinkedList.

Useful for scenarios requiring versatile insertion and removal operations.

ArrayDeque:

Implements the Deque interface, a resizable array-based double-ended queue.

Efficient for adding or removing elements from both ends.

Map Hierarchy:

Map Interface

Remember, the Map interface in Java is not directly a part of the collection hierarchy; instead, it is a separate interface that extends the java.util.Collection interface indirectly.

    - Represents a collection of key-value pairs.

    - Key implementations include HashMap and TreeMap.

    - Allows mapping unique keys to values, facilitating efficient data retrieval.

HashMap:

  - Implements the Map interface and uses hash table for storage.

  - Provides constant-time performance for basic operations on average.

  - Allows null values and one null key.

LinkedHashMap:

Extends HashMap, preserving the order of key insertion.

Useful when iterating over entries requires a predictable order.

TreeMap:

  - Also implements the Map interface but maintains key-value pairs in sorted order.

  - Utilizes a red-black tree for storage.

  - Suitable when a sorted map based on the natural order of keys is required.