Lecture 74:-  Collection Heirarchy

The Java Collections Framework is organized as a hierarchy of interfaces and classes, which provides a unified and consistent way to work with different types of collections. The hierarchy is based on several key interfaces and their subinterfaces, and classes that implement these interfaces. Here's an overview of the collection hierarchy:

1. Collection Interface:
   • The root interface of the collection hierarchy is the Collection interface.
   • It extends the Iterable interface, which allows collections to be iterated using the enhanced for loop (for-each loop).
   • Subinterfaces of Collection include:
     • List: An ordered collection that allows duplicate elements.
     • Set: A collection that does not allow duplicate elements.
     • Queue: A collection used to hold elements before processing, following FIFO or priority-based order.
2. List Interface:
   • The List interface extends the Collection interface and introduces additional methods to access elements by index and perform positional operations (e.g., add, remove).
   • Implementing classes: ArrayList, LinkedList, Vector, etc.
3. Set Interface:
   • The Set interface extends the Collection interface and enforces uniqueness of elements. It does not allow duplicate elements.
   • Implementing classes: HashSet, TreeSet, LinkedHashSet, etc.
4. Queue Interface:
   • The Queue interface extends the Collection interface and represents a collection that supports operations based on the First-In-First-Out (FIFO) principle.
   • Implementing classes: LinkedList, PriorityQueue, etc.
5. Map Interface:
   • The Map interface is not a subtype of Collection, but it is an important part of the Java Collections Framework.
   • It represents a key-value pair collection, where each key is associated with a value, and keys are unique within the map.
   • Implementing classes: HashMap, TreeMap, LinkedHashMap, etc.
6. SortedSet and SortedMap Interfaces:
   • SortedSet: An extension of the Set interface that maintains elements in sorted order.
   • SortedMap: An extension of the Map interface that maintains keys in sorted order.
7. NavigableSet and NavigableMap Interfaces:
   • NavigableSet: An extension of the SortedSet interface that provides navigation methods to access elements based on their position in the set.
   • NavigableMap: An extension of the SortedMap interface that provides navigation methods to access entries based on their position in the map.

The Java Collections Framework provides various classes that implement these interfaces, offering different data structures and implementations to suit specific needs. Developers can choose the appropriate collection type based on their requirements and take advantage of the rich functionality provided by the interfaces and classes in the hierarchy.