1. The Collection Framework

2. Collections Framework
 A collection is a group of objects.
 The Collection Framework Standardizes the way in
which group of objects are handled by your program.
What c++ calls a Container,Java calls a Collection

3. The Collection interfaces
 Collection- enable you to work with groups of
objects.
 List- extends collection to handle sequences.
 Set- extends collection to handle sets, which must
contain unique elements.

4. The Collection Classes
 ArrayList – implements a dynamic array.
 LinkedList – implements a linked list.
 HashSet – uses hash table.
 linkedHashSet – allow insertion-order iterations.
 TreeSet – implements a set stored in a tree.

5. ArrayList class
 ArrayList class implements the List interface.
 ArrayList supports dynamic arrays that can grow as needed.
 It is a Variable length array of object references.
 ArrayLists are created with an initial size. When this size is
enlarged, the collection is automatically enlarged. And when the
objects are removed, the array may be shrunk.

6. Using constructor
 ArrayList()
 ArrayList(Collection c)
 ArrayList(int capacity)

7. Methods and Examples
 Create an array list
ArrayList a1 = new ArrayList();
 Add elements to the array list
a1.add(“c”);
a1.add(1,“A2”);

8.  Display the array list
System.out.println(a1);
 Remove elements from the array list
a1.remove(“F”);
a1.remove(2);
 For finding the size of arrayList
a1.size();

9. Obtaining an Array from an ArrayList
 Add elements to the array list
a1.add(new Integer(1));
 Get array
object ia[ ] = a1.toArray();

10. LinkedList Class
 LinkedList class extends AbstractSequentialList and
implements the List interface.
 It provides a linked list data structure.

11. Constructor
 LinkedList()
 LinkedList(collection c)

12. Methods
 To add elements at the first /last position.
addFirst();
addLast();
 To retrieve the elements at first /last position.
getFirst();
getLast();
 To remove the elements at first /last position.
removeFirst();
removeLast();

13. TreeSet class
 TreeSet provides an implementations of the Set
interface that uses a tree for storage.
 Objects are stored in sorted order i.e ascending
order.
 Access and retrieval times are quite fast.

14. Constructors
 TreeSet()
 TreeSet(collection c)
 TreeSet(comparator comp)
 TreeSet(SortedSet ss)

15. Example
Import java.util.*;
Class TreeSetDemo
{
Public static void main(String args[])
{
TreeSet ts=new TreeSet();
ts.add(“C”);
ts.add(“A”);
ts.add(“B”);
System.out.println(ts);
}
}
Output- [A,B,C]

16. HashSet class
 HashSet extends AbstractSet and implements the Set
interface.
 It creates a collection that uses a hash table for storage.
 Basic operations:
add()
contains()
remove()
size()

17. Using constructor
 HashSet()
 HashSet(collection c)
 HashSet(int capacity)
 HashSet(int capacity, float fillRatio)

18. Methods
 boolean add(Object o)
 void clear()
 Object clone()
 boolean contains(Object o)
 boolean isEmpty()
 Iterator iterator()
 boolean remove(Object o)
 int size()

19. Example
import java.util.*;
class hashset
{
public static void main(String args[])
{
HashSet hs = new HashSet();
hs.add("B");
hs.add("A");
hs.add("D");
hs.add("E");
hs.add("C");
hs.add("F");
System.out.println(hs);
hs.remove("C");
System.out.println("elements after removing C"+hs);
}
}

20. LinkedHashSet class
 LinkedHashSet extends HashSet, but adds no
members of its own.
 LinkedHashSet maintains a linked list of the entries
in the set.

21. Using constructor
 LinkedHashSet( )
 LinkedHashSet(Collection c)
 LinkedHashSet(int capacity)
 LinkedHashSet(int capacity, float fillRatio)

22. Remove all elements from LinkedHashSet
import java.util.LinkedHashSet;
public class linkedhashset
{
public static void main(String[] args)
{
LinkedHashSet lhashSet = new LinkedHashSet();
lhashSet.add(new Integer("1"));
lhashSet.add(new Integer("2"));
lhashSet.add(new Integer("3"));
System.out.println("LinkedHashSet before removal : " + lhashSet);
lhashSet.clear();
System.out.println("LinkedHashSet after removal : " + lhashSet);
System.out.println("Is LinkedHashSet empty ? " + lhashSet.isEmpty());
}
}

23. House Is Open For Queries