Collections Framework

Collections Framework Package: java.util

• The Java collections framework provides a set of interfaces and classes to implement various data structures and algorithms.
• Java Collections can achieve all the operations that you perform on a data such as searching, sorting, insertion, manipulation, and deletion.
• Java Collection framework provides
• interfaces (Set, List, Queue, Deque)
• classes (ArrayList, Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet, TreeSet).
• Advantages
• Reduces programming effort
• Increases program speed.
• Reduces effort to learn and to use new APIs

Hierarchy of Collection Framework

Collection Interface

• The Collection interface is the root interface of the Java collections framework.
• There are three interface implement List, set and Queue.
• Collection is group of objects.
• This interface defines the standard which must be followed by all collection type of objects.

• public boolean add(Object obj)
• to add an element.
• public boolean addAll(Collection c)
• to add all elements of collection.
• public boolean remove(Object element)
• to delete an element.
• public int size()
• It returns the total number of elements.
• public void clear()
• removes all elements.
• public boolean removeAll(Collection c)
• to delete all the elements present in specified collection.
• public boolean retainAll(Collection c)
• to delete all the elements except the specified collection.
• public boolean contains(Object element)
• It is used to search an element.
• public Iterator iterator()
• It returns an iterator.
• public Object[ ] toArray()
• It converts collection into array.
• public boolean isEmpty()
• It checks if collection is empty.

List Interface

• It defines Standard for ordered collection.
• List Interface is implemented by ArrayList, LinkedList, Vector and Stack classes.

• void add(int index, Object obj)
• Inserts obj into the list at the index.
• boolean addAll(int index, Collection c)
• Inserts all elements of c into the list at the index.
• Object remove(int index)
• Removes the element at position index list and returns the deleted element.
• Object set(int index, Object obj)
• Sets object at the location.
• It returns the replaced element.
• Object get(int index)
• Returns the object stored at the specified index.
• int indexOf(Object obj)
• Returns the index of the first instance of obj.
• If obj is not in list, -1 is returned.
• int lastIndexOf(Object obj)
• Returns the index of the last instance of obj.
• If obj is not in list, -1 is returned.
• ListIterator listIterator( )
• Returns an iterator to the start of the list.
• ListIterator listIterator(int index)
• Returns an iterator to the list that begins at the specified index.
• List subList(int start, int end)
• Returns a list that includes elements from start to end-1 in the list.