Collections
Mr. Madar Bandu
The Collection in Java is a framework that provides an
architecture to store and manipulate the group of objects.
Java Collections can achieve all the operations that you
perform on a data such as searching, sorting, insertion,
Collections... manipulation, and deletion.
Java Collection means a single unit of objects. Java
Collection framework provides many interfaces (Set, List,
Queue, Deque) and classes (ArrayList,
Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet,
TreeSet).
List interface is the child interface
of Collection interface. It inhibits a
list type data structure in which we List interface is implemented by
can store the ordered collection of the classes ArrayList, LinkedList.
objects. It can have duplicate
values.
List Interface
List <data-type> list1= new ArrayList();
List <data-type> list2 = new LinkedList();
The ArrayList class implements the List
interface. It uses a dynamic array to store the
duplicate element of different data types.
The ArrayList class maintains the insertion
order and is non-synchronized.
ArrayList
The elements stored in the ArrayList class
can be randomly accessed
• boolean add(Object o)
• int size()
• void clear()
• Object get(int index)
• int indexOf(Object o)
ArrayList • int LastIndexOf(Object o)
Methods • Object remove(int index)
• Bolean remove(Object o)
ArrayList...
import java.util.*;
class TestJavaCollection1{
public static void main(String args[]){
ArrayList<String> list=new ArrayList<String>();
list.add("Ravi");//Adding object in arraylist
list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
//Traversing list through Iterator
Iterator itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
LinkedList implements the Collection
interface. It uses a doubly linked list
internally to store the elements.
It can store the duplicate elements. It
LinkedList maintains the insertion order and is
not synchronized.
In LinkedList, the manipulation is fast
because no shifting is required.
• boolean add(Object o)
• int size()
• void addFirst(Object o)
• void addLast(Object o)
• void clear()
• Object get(int index)
• Object getFirst()
LinkedList • Object getLast()
• int indexOf(Object o)
• int LastIndexOf(Object o)
• Object remove(int index)
• Bolean remove(Object o)
• Object removeFirst()
• Object removeLast()
LinkedList
import java.util.*;
public class TestJavaCollection2{
public static void main(String args[]){
LinkedList<String> al=new LinkedList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator<String> itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Queue interface maintains the first-in-first-out order. It
can be defined as an ordered list that is used to hold
the elements which are about to be processed.
There are various classes like PriorityQueue, Deque,
and ArrayDeque which implements the Queue
Queue interface.
Interface Queue<String> q1 = new PriorityQueue();
Queue<String> q2 = new ArrayDeque();
The PriorityQueue class implements
the Queue interface. It holds the
elements or objects which are to be
processed by their priorities.
PriorityQueue
PriorityQueue doesn't allow null
values to be stored in the queue.
PriorityQueue
import java.util.*;
public class TestJavaCollection5{
public static void main(String args[]){
PriorityQueue<String> queue=new PriorityQueue<String>();
queue.add("Amit Sharma");
queue.add("Vijay Raj");
queue.add("JaiShankar");
queue.add("Raj");
System.out.println("head:"+queue.element());
System.out.println("head:"+queue.peek());
System.out.println("iterating the queue elements:");
Iterator itr=queue.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
queue.remove();
queue.poll();
System.out.println("after removing two elements:");
Iterator<String> itr2=queue.iterator();
while(itr2.hasNext()){
System.out.println(itr2.next());
}
}
}
Set Interface in Java is present in java.util package. It extends
the Collection interface.
It represents the unordered set of elements which doesn't
allow us to store the duplicate items.
We can store at most one null value in Set. Set is
implemented by HashSet, LinkedHashSet, and TreeSet.
Set Interface
Set<data-type> s1 = new HashSet<data-type>();
Set<data-type> s2 = new LinkedHashSet<data-type>();
Set<data-type> s3 = new TreeSet<data-type>();
HashSet class implements Set
Interface. It represents the
collection that uses a hash
table for storage.
HashSet
Hashing is used to store the
elements in the HashSet. It
contains unique items.
HashSet...
import java.util.*;
public class TestJavaCollection7{
public static void main(String args[]){
//Creating HashSet and adding elements
HashSet<String> set=new HashSet<String>();
set.add("Ravi");
set.add("Vijay");
set.add("Ravi");
set.add("Ajay");
//Traversing elements
Iterator<String> itr=set.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
} }
}
LinkedHashSet class represents the
LinkedList implementation of Set
Interface.
It extends the HashSet class and
LinkedHashSet implements Set interface. Like HashSet,
It also contains unique elements.
It maintains the insertion order and
permits null elements.
LinkedHashSet...
import java.util.*;
public class TestJavaCollection8{
public static void main(String args[]){
LinkedHashSet<String> set=new LinkedHashSet<String>();
set.add("Ravi");
set.add("Vijay");
set.add("Ravi");
set.add("Ajay");
Iterator<String> itr=set.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
TreeSet class implements the Set
interface that uses a tree for
storage. Like HashSet, TreeSet
also contains unique elements.
TreeSet
However, the access and
retrieval time of TreeSet is quite
fast. The elements in TreeSet
stored in ascending order.
TreeSet...
import java.util.*;
public class TestJavaCollection9{
public static void main(String args[]){
//Creating and adding elements
TreeSet<String> set=new TreeSet<String>();
set.add("Ravi");
set.add("Vijay");
set.add("Ravi");
set.add("Ajay");
//traversing elements
Iterator<String> itr=set.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Any Queries?
