Collections in java is a framework that provides an architecture to store and manipulate the group of objects.
Collection framework is a set of classes and interfaces which provide unified model (combine model) of working with different types of Collections. At the core of collection framework is an interface names Collection. This interface defines common functionality of all Collections. Java.util package contain classes and interfaces of collection framework. Classes like ArrayList, Vector,LinkedList, HashSet, TreeSet, LinkedHashSet, HashMap etc. use to add, reterive, remove, find and iterate the objects
Collection represents a single unit of objects i.e. a group.
The java.util package contains all the classes and interfaces for Collection framework.
There are many methods declared in the Collection interface. They are as follows:
|1||public boolean add(Object element)||is used to insert an element in this collection.|
|2||public boolean addAll(collection c)||is used to insert the specified collection elements in the invoking collection.|
|3||public boolean remove(Object element)||is used to delete an element from this collection.|
|4||public boolean removeAll(Collection c)||is used to delete all the elements of specified collection from the invoking collection|
|5||public public boolean retainAll(Collection c)||is used to delete all the elements of invoking collection except the specified collection.|
|6||public int size()||return the total number of elements in the collection|
|7||public void clear()||removes the total no of element from the collection.|
|8||public boolean contains(object element)||is used to search an element.|
|9||public boolean containsAll(Collection c)||is used to search the specified collection in this collection.|
|10||public Iterator iterator()||returns an iterator.|
|11||public Object toArray()||converts collection into array.|
|12||public boolean isEmpty()||checks if collection is empty.|
|13||public boolean equals(Object element)||matches two collection.|
|14||public int hashCode()||returns the hashcode number for collection.|
Iterator interface provides the facility of iterating the elements in forward direction only. Methods of Iterator interface There are only three methods in the Iterator interface. They are: