Collection Framework

Collection is kind of a container which is simply an object or groups of multiple object into a single package. Collections are used to store, manipulate and retrieve data. The real world example, such as a pack of cards , telephone directory and vegetable basket with vegetables. Collection was introduced in-JDK 1.2 versions of the Java platform. Before JDK 1.2, Some standard methods for grouping Java objects via array, Vector Hashtable classes.

Collections framework is unified architecture for representing and manipulating collections. It is contains a set of classes and interfaces that achieve to implementation of data structures.

Collections frameworks contain the following:

• Interfaces: These are abstract data types that represent collections.
• Implementations: These are the concrete implementations of the collection interfaces for reusable data structures.
• Algorithms: These are some methods that perform useful computations, such as searching,sorting, on objects that implement collection interfaces.

Advantages

• Reduces effort of programming
• Increases performance and quality
• Reduces effort to learn and design new APIs:

core collection interfaces

Core collection interfaces are the foundation of the Java Collections Framework. you can see below figure, the core collection interfaces form a hierarchy.

The following list describes the core collection interfaces:

• Iterable : This interface allows an object to be the target of the "for-each loop" statement.
• Collection : The root of the collection hierarchy. A collection represents a group of objects. Collection interface is the interface which is implemented by all the classes in the collection framework. This interface builds the foundation on which the collection framework .
• Set : A collection that cannot contain duplicate elements
• SortedSet : Set is maintain ascending order of elements.
• List : A collection that can contain duplicate elements and specific ordered. its allow, elements can be placed in a specific position.
• Queue : A collection used to hold multiple elements prior to processing. Besides basic Collection operations, a Queue provides additional insertion, extraction. Typically, queues stores elements in the order in which they are inserted. New additions go to the end of the line, and elements are removed from the front. It creates a first-in first-out (FIFO) system. but do not necessarily. priority queues is exceptions. Every Queue implementation must specify its ordering properties.
• Deque : A collection creates a double-ended queue. While a regular queue only allows insertions at the rear and removals at the front, but deque allows insertions or removals to take place both at the front and the back. It is used both as FIFO (first-in, first-out) and LIFO system.
• Map: Object that contain keys to values pair. it cannot contain duplicate keys. each key can map to at most one value.
• SortedMap : Map is maintains ascending key order mapping.

The java.util package contains all the classes and interfaces for the Collection framework.

Iterable

Interface Iterable<T> : This interface is an object to be target of the "for-each loop" statement.

Abstract method.

Iterator<T> iterator(); //It returns the iterator elements T type  

Default method

1) forEach(Consumer<? super T> action)

2) spliterator()

Iterator

Interface Iterator<E> : Iterator interface represents an object capable of iterating through a collection of objects, one object at a time. Iterator takes the place of Enumeration in the Java Collections Framework. Iterator is differ from enumeration in two ways:

• Iterator allow to caller for remove elements from the specific collection during the iteration of elements
• Method names have been refined.

Abstract method.

1) hasNext() //Returns true if the iteration has more elements.

2) next()    //Returns the next element in the iteration.

Collection

Interface Collection<E> :