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.
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.
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.
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()
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());
}
}
