The Java Collections Framework is a comprehensive framework defined in JDK 1.2, which includes all the collection classes and interfaces. A collection is a group of individual objects that are represented as a single unit. The Collection interface (java.util.Collection) and Map interface (java.util.Map) are the two main “root” interfaces of Java collection classes.
The Collection Framework offers several advantages that reduce programming effort and increase program speed and quality. Programmers can focus on using collections in their programs instead of worrying about designing them, thanks to the framework's abstraction concept, which implements Object-oriented programming. Additionally, the framework provides high-performance implementations of useful data structures and algorithms, which increases program performance. Moreover, the API has a basic set of interfaces such as Collection, Set, List, or Map, which have a common set of methods.
The Collection Framework has several implementations of data structures, including Lists, Sets, Queues, Deques, and Maps. The List interface defines an ordered collection of elements that allows duplicate entries. The ArrayList provides dynamic arrays in Java, and its size is automatically increased or decreased based on the collection's growth. The LinkedList class is an implementation of the DoublyLinkedList data structure. The Vector class provides dynamic arrays, but it is not recommended to be used in a single-threaded environment as it might cause extra overheads.
The Set interface represents a collection of unique elements. The HashSet class implements the hash table data structure, and the TreeSet class implements the Self-balancing binary tree like red-black tree. The LinkedHashSet is similar to HashSet but retains the ordering of the elements.
The Queue interface maintains the First In First Out (FIFO) order similar to a real-world queue line. The LinkedList class implements Queue data-structure, and the ArrayDeque class provides a way to apply resizable-array. The PriorityQueue class is used when the objects are supposed to be processed based on priority.
The Deque interface, also known as a double-ended queue, is a data structure where we can add and remove elements from both ends of the queue. This interface extends the queue interface. The LinkedList class implements this interface using a linked list implementation, and the ArrayDeque class uses an array implementation.
The Map interface is a data structure that supports the key-value pair mapping for the data. The HashMap uses a technique called Hashing, which provides the basic implementation of the Map interface of Java. The LinkedHashMap is similar to HashSet, but it uses a doubly linked list to store the data and retains the ordering of the elements.
Finally, the Collections class provides implementation of basic algorithms like binarySearch(), sort(), max(), min(), reverse(), fill(), etc. These algorithms are implemented on the above mentioned collection frameworks, providing consistency and reducing programming effort.