Java Collection Framework Overview

Java Collections II

Java's collection framework is a set of interfaces and classes that provide various data structures and algorithms. It offers a set of operations common to all collection classes. The framework is divided into two main interfaces: the Collection interface and the Map interface. The Collection interface, in turn, has subinterfaces such as List, Set, and Queue.

Collection Interface

The Collection interface is the root interface in the collection hierarchy. It extends the Iterable interface and provides methods for basic collection operations like adding and removing elements and checking the emptiness of the collection. However, it does not provide a specific implementation for these operations. Instead, it leaves these operations to be implemented by the classes that extend the Collection interface.

List Interface

The List interface is a child interface of the Collection interface and is dedicated to ordered collections of objects. It allows duplicate elements to be present in the collection. Some classes that implement the List interface are ArrayList, Vector, and Stack.

Set Interface

The Set interface allows for the storage of elements in an unordered manner, ensuring that there are no duplicate elements in the collection. Some classes that implement the Set interface are HashSet and TreeSet.

Queue Interface

The Queue interface is used when elements are to be stored and accessed in a first-in, first-out (FIFO) manner. Some classes that implement the Queue interface are LinkedList and PriorityQueue.

HashMap, TreeMap, LinkedHashMap

These are all implementations of the Map interface, which allows elements to be stored in key-value pairs. The key is unique and can be used to access the corresponding value. The main differences between these classes are their specific implementations of the Map interface.

HashMap

HashMap is a hash table implementation of the Map interface. It provides faster access to elements than TreeMap and LinkedHashMap.

TreeMap

TreeMap is a sorted variant of HashMap, which maintains the elements in sorted order based on the natural ordering of their keys. It provides faster access to elements in sorted order than HashMap.

LinkedHashMap

LinkedHashMap is a hash table implementation of the Map interface with a linked list for iterating over the entries. It is useful when we need to iterate over the elements in the order they were added to the map.

LinkedHashSet, HashSet

These are implementations of the Set interface. The main difference between them is their implementation of the Set interface.

LinkedHashSet

LinkedHashSet is a hash set implementation with a linked list for iterating over the elements. It maintains the elements in the order they were added to the set.

HashSet

HashSet is a simple hash set implementation of the Set interface. It provides faster access to elements than LinkedHashSet and does not offer any specific order for iterating over the elements.

Collection Framework

The collection framework in Java provides a set of interfaces and classes to implement various data structures and algorithms. It allows users to choose a specific data structure for a particular type of data. The framework is highly optimized and provides methods for performing operations like adding, removing, and accessing elements in collections.