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- Collections in java is a framework that provides an architecture to store and manipulate the group of objects.
- All the operations that you perform on a data such as searching, sorting, insertion, manipulation, deletion etc. can be performed by Java Collections.
- Java Collection simply means a single unit of objects. Java Collection framework provides many interfaces (Set, List, Queue, Deque etc.) and classes (ArrayList, Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet, TreeSet etc).
What is Collection in java
- Collection represents a single unit of objects i.e. a group.
What is framework in java
- provides readymade architecture.
- represents set of classes and interface.
- is optional.
What is Collection framework
Collection framework represents a unified architecture for storing and manipulating group of objects. It has:
- Interfaces and its implementations i.e. classes
Hierarchy of Collection Framework
Let us see the hierarchy of collection framework.The java.util package contains all the classes and interfaces for Collection framework.
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Methods of Collection interface
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 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:
|1||public boolean hasNext()||It returns true if iterator has more elements.|
|2||public Object next()||It returns the element and moves the cursor pointer to the next element.|
|3||public void remove()||It removes the last elements returned by the iterator. It is rarely used.|