In this chapter you will learn:

1. What is ArrayDeque?
2. Declaration of ArrayDeque
3. Programming Example

ArrayDeque is a resizable array implementation in Deque. Some fact about ArrayDeque are as follow:

• It is a resizable array implementation in Deque.
• It has no capacity restriction so it grows as necessary.
• It is not thread safe
• It doesn’t allow null element
• It is faster than stack when used as stack and faster than linked list when used as linked list.

Constructors

Methods

Methods Inherited From Class

Declaration:

ArrayDeque aq=new ArrayDeque();

Programming Example

import java.util.*;
class ArrayDeque_Example
{
  public static void main(String[] args)
  {
    ArrayDeque aq=new ArrayDeque();
    aq.push("C#");
    aq.push("Java");
    aq.push("HTML");
    aq.push("ASP.Net");
    
    //Printing ArrayDeque
    Iterator itr=aq.iterator();
    while(itr.hasNext())
    {
      System.out.print(itr.next()+ " ");
    }
    
    //Removing one Item
    System.out.println("\nItem Removed : " + aq.pop());
    
    //Printing ArrayDeque Again
    System.out.println(aq);
    
    //Adding Element at First Position
    aq.addFirst("PHP");
    //Adding Element at Last Position
    aq.addLast("JavaScript");
    
    //Printing ArrayDeque
    System.out.println(aq);
    
    //Finding Element
    if(aq.contains("Java"))
    {
      System.out.println("Java is found in this list");
    }
  }
}

Output

Summary

In this chapter you have learned ArrayDeque in Java. It is very easy to learn collection using complete programming example. In the next chapter you will learn Set Interface in Java.

In this chapter you will learn:

1. What is Deque in Java?
2. Declaration of Deque
3. Programming Example

Keyword Deque stands for “Double Ended Queue” which allows insertion and removal of both sides. You can add and remove element both sides as head and tail. However Deque has not size limit but using interface you can restrict its size limit. There are some special methods which allow element’s insertion and removal in both sides. Deque can also be used as Stack. It can behave like LIFO and FIFO both.

Methods

Compare Methods (Queue Vs. Deque)

Deque d=new LinkedList();

Programming Example

import java.util.*;
class DeQue_Example
{
  public static void main(String[] args)
  {
    Deque d=new LinkedList();
    
    d.addLast("Tail1");
    d.addLast("Tail2");
    d.addFirst("Head1");
    d.addFirst("Head2");
    
    //Print Deque using Iterator
    Iterator itr=d.iterator();
    while(itr.hasNext())
    {
      System.out.print(itr.next() + " ");
    }
    System.out.println("\nPeek Last Value : "+d.peekLast());
    System.out.println("Remove Last Value : "+d.pollLast());
    //Adding new value to last
    d.addLast("Hello");
    System.out.println("printing : "+d);
  }
}

Output

Summary

In this program you can clearly see that Deque allows insertion and removal of elements both sides. It has some special methods that allows programmer to use deque as stack. In the next chapter you will learn about ArrayDeque Class.

In this chapter you will learn:

1. What is PriorityQueue?
2. Programming Example

Java PriorityQueue are unbounded queue based on priority heap. It store element according to their natural ordering and doesn’t allow null insertion. It is likely as random listing of element in a queue. Important points of PriorityQueue are as follow:

• It is unbounded and based on Priority heap.
• However it is unbounded still it has internal capacity to manage size of queue. Size of queue grows automatically if it reaches as maximum elements.
• Order of elements gets defined based on constructors.
• Methods, property and iterator are same as queue interface.

Constructors and Methods

Methods and Descriptions

Methods Inherited From Class

Declaration:

PriorityQueue p=new PriorityQueue();

Programming Example

import java.util.*;
class PriorityQueue_Example
{
  public static void main(String[] args)
  {
    PriorityQueue p=new PriorityQueue();
    //Adding Element in PriorityQueue
    p.add("C#");
    p.add("Java");
    p.add("C++");    
    p.add("HTML");
    p.add("VB.Net");
    
    //Printing PriorityQueue
    Iterator itr=p.iterator();
    while(itr.hasNext())
    {
     System.out.print(itr.next()+" "); 
    }
    
    //Adding Elements
    p.add("PHP");
    System.out.println("\n" + p);
    
    //Accessing Top Element
    System.out.println("Top Element is "+ p.element());
    
    //Removing Top Element
    System.out.println("Item Removed : " + p.remove());
    
    //Prining PriorityQueue
    System.out.println(p);
    
  }
}

Output

Summary

In this chapter you have learned about PriorityQueue in Java. It organizes their element order after removing each item. It is mostly used for random listing of elements in a queue. In the next chapter you will learn about Deque Class in Java.

In this chapter you will learn:

1. What is queue interface?
2. Queue Structure
3. Programming Example

Queue is a part of java collection that follows FIFO structure for holding elements. FIFO is based on First In First Out that means the first inserted element will be processed first. There are various real life examples of Queues are:

• Ticket Counter Queue – The First person in the line gets chance to buy ticket first.
• Bus Queue – First position bus will start first.
• Billing Counter – First customer in the line will pay the bill first.

More about Queue

1. Queue has additional insertion, removal and inspection operations besides on basic collection operations.
2. Each Queue operation gets terminated by two methods either by throwing exception or by returning special value as null or false.
3. Each queue has two parts head and tail. Items inserted in queue through tail side and remove item through head side.
4. Bounded queue holds only specified number of elements.
5. Add() method is used for inserting element in a queue and remove() or poll() method is used for removing items from queue.
6. Queue doesn’t allow the insertion of null.

Declaration

Queue queue = new LinkedList();

Programming Example

import java.util.*;
class Queue_Example
{
  public static void main(String[] args)
  {
    Queue q=new LinkedList();
    //Adding Item in a queue
    q.add("Java");
    q.add("C#");
    q.add("VB.Net");
    q.add("C++");
    q.add("PHP");
    //Size of Queue
    System.out.println("Size of queue : "+q.size());
    //Displaying Queue
    Iterator itr=q.iterator();
    while(itr.hasNext())
    {
      System.out.print((String)itr.next()+ " ");
    }
   //Retrieving Queue Element
    System.out.println("\nTop Item is "+q.peek());
    //Remove Top Element
    System.out.println("Items Removed "+q.remove());
    //Again printing queue
    System.out.println(q);
    //Size of Queue
    System.out.println("Size of queue : "+q.size());
    //Adding an Item
    q.add("HTML");
    //Printing Queue
    System.out.println(q);
  }
}

Output

Summary

In this chapter you learned what the queue interface is in java and their methods and implementation with programming example. In the next chapter you will learn PriorityQueue class.

In this chapter you will learn:

1. What is stack class in java?
2. How to initialize stack?
3. Methods of stack class
4. Programming Example

Stack is based on Last-in-First-Out (LIFO) module. It is a subclass of vector class. In the stack the item which is added first in the list can be accessed last and the item which is added last can be accessed first.
For example:

• Wearing bangles.
• Stack of CD.
• Stack of Book etc

How to declare stack?

 public class Stack
   extends Vector

Constructors and methods

It includes all the methods of vector class and it also defines several other methods.

Programming Example

import java.util.*;
public class Stack_Example
{
  public static void main(String[] args)
  {
    //Create Empty Stack
    Stack stk=new Stack();
    System.out.println("Items on Stack : " + stk);
    
    //Adding items to Stack
    stk.push("A");
    stk.push("B");
    stk.push("C");
    try
    {
    //Retrieving Stack
    System.out.println("Removing Top Items : " + stk.pop());
    System.out.println("Now items are : " + stk);
    
    System.out.println("Removing Top Items : " + stk.pop());
    System.out.println("Now items are : " + stk);
    
    System.out.println("Removing Top Items : " + stk.pop());
    System.out.println("Now items are : " + stk);
    
    System.out.println("Removing Top Items : " + stk.pop());
    System.out.println("Now items are : " + stk);
    }
    catch(EmptyStackException e)
    {
      System.out.println("Stack Empty");
    }
    
  }
}

Output

Explanation

In the above example we push() method is used for adding items on the stack and pop()method is used for removing items from the top.

Summary

In this chapter you have learned stack class in java collection and their methods with complete programming example. In the next chapter you will learn Queue Interface in Java.

In this chapter you will learn:

1. What is Vector Class in Java?
2. Difference between ArrayList and Vector
3. Initialization of Vector Cass
4. Methods of Vector Class in Java
5. Programming Example

Vector is like an array but the difference is that it can grow and shrink dynamically and doubly. Like an array the element of vector can also be accessed through its index position. It optimizes storage management by maintaining capacity and capacityIncrement. It means if you remove an element the size of vector automatically decreases. Vector Class has synchronized behavior so it gives weak performance in searching, adding, delete and update of its elements.

How to Initialize Vector?

There are three way to initialize vector.

1. Vector V=new Vector();

It is the default way to create vector. It creates an empty vector with the size of 10. The size of vector will grow when it needs 11th items.

2. Vector object= new Vector(int initialCapacity)
Vector vc=new Vector(5);

It will create vector with initial size 5.

3. Vector object= new vector(int initialcapacity, capacityIncrement)
Vector vec= new Vector(4, 6)

It will create vector with size 4 and increment capacity is 6. It means when you add 5th element in the list the size of vector will be increased by 6 and capacity of vector will be 10.

Different Between ArrayList and Vector

Constructors of Vector class

Methods of Vector Class

Programming Example

import java.util.*;
class Vector_Class
{
  public static void main(String[] args)
  {
    //Initial size is 2
    Vector v=new Vector(2);
    v.addElement("Laptop");
    v.addElement("Desktop");
    v.addElement("iPhone");
    System.out.println(v);
    System.out.println("Vector Size is "+v.size());
    System.out.println("Default Capacity Increment is "+v.capacity());
    System.out.println("If Contains iPhone : "+v.contains("iPhone"));
    System.out.println("First Element is : "+v.firstElement());
    System.out.println("Last Element is : "+v.lastElement());
    System.out.println("Index Position of Desktop : "+v.indexOf("Desktop"));
    System.out.println("Is Vector Empty ? : " +v.isEmpty());
    //Adding Mobile at index position 2
    v.add(2,"Mobile");
    System.out.println("New List is after adding Mobile : "+v);
    //Removing Desktop
    v.remove("Desktop");
    System.out.println("New List is after removing Desktop : "+v);
    
    //Iterate through Iterator Interface
    System.out.println("Elements are : ");
    Iterator itr=v.iterator();    
    while(itr.hasNext())
    {
      System.out.print(itr.next() + " , ");
    }
    
    //Traverse using Enumertion
    System.out.println("\nElements are : ");
    Enumeration en=v.elements();
    while(en.hasMoreElements())
    {
      System.out.print(en.nextElement() + " , ");
    }    
  }
}

Output

Summary

In this chapter you have learned all about Vector class in Java. Vector is like an array list but the difference is that is synchronized and exceeds its capacity size doubly. In the next chapter you will learn Stack Class in Java.

In this chapter you will learn:

1. What is LinkedList Class in Java?
2. Methods of Linked List Class
3. Programming Example

Java LinkedList class uses doubly linked list structure to store element in the list. It extends the abstract class and implements List and Deque Interface. Java LinkedList class can contains null value or duplicate value. LinkedList class doesn’t support synchronization. It means if more than one thread is accessing Linked List simultaneously and one thread makes some changes the Linked List must be externally synchronized. Manipulation of Linked List is faster than ArrayList because no shifting needs to be occurred.

Initialization

You can define LinkedList class as follow. You must include java.util.*; in your program.

LinkedList list=new LinkedList();

Constructors of LinkedList class

Methods of ArrayList Class

Programming Example

import java.util.*;

class Linked_List
{
  public static void main(String[] args)
  {
    LinkedList<String> list=new LinkedList<String>();
    list.add("Computer");
    list.add("Mobile");
    list.add("Tablet");
    list.add("iPhone");
    
    //Adding an item at the begining of the list
    list.addFirst("iPad");
    System.out.println(list);
    
    //Adding an item at the last position of the list
    list.addLast("Laptop");
    System.out.println(list);
   
    //Making clone
    Object obj=new Object();
    obj=list.clone();
    System.out.println("Clone : "+obj);
    
    //Remove item at index position 2
    System.out.println("Items Removed : "+list.remove(2));
    
    //Printing Using Iterator
    Iterator<String> itr=list.iterator();
    while(itr.hasNext())
    {
      System.out.print(itr.next()+" , ");
    }
  }
}

Output

Summary

In this chapter you have learned what is LInkedList class and their methods in Java with complete programming example. In the next chapter you will learn about Vector Class in Java.

In this chapter you will learn:

1. What is ArrayList class?
2. Methods of ArrayList class
3. Programming Example

ArrayList is such type of storage array which is dynamic in size and can grow and shrink at runtime. It is actually a resizable array. It implements the list interface and has almost same operations as lists but it doesn’t allow null value.

Initialization

You can define ArrayList class as follow. You must include java.util.*; in your program.

ArrayList alist=new ArrayList();

Constructors of ArrayList class

Programming Example

import java.util.*;

class Array_List
{
  public static void main(String[] args)
  {
    ArrayList alist=new ArrayList();
    alist.add("Table");
    alist.add("Chair");
    alist.add("Speaker");
    alist.add("Guitar");
    alist.add("Fan");
    
    //Printing arraylist item
    System.out.print("All Array List Items are ");
    System.out.println(alist);
    
    //Adding new item at index position 2
    alist.add(2, "Calculator");
    System.out.println("Adding Calculator : "+alist);
    
    //Removing item Calculator
    alist.remove("Calculator");
    System.out.println("Removing Calculator : "+alist);
    
    //Get element name at specified index position
    System.out.println("Element at Index Position 2 : " + alist.get(2));
    
    //Get total size of arraylist
    System.out.println("ArrayList Size are : " + alist.size());
    
    //Clear the arraylist
    alist.clear();
    System.out.println("After clearing arraylist " + alist);
  }
}

Output

Summary

ArrayList is very useful when you don’t know how many items have to be added in the list. It can be shrink and grow dynamically at runtime. This chapter also explains all the methods or ArrayList class with programming example. It is very easy to learn this keyword in this chapter. The next chapter is explaining one more List item LinkedList.

In this chapter you will learn:

1. What is List Interface in Java Collection?
2. List Interface methods
3. Iterator and ListIterator Interface

A list is an order collection which stores item at exact position where it is added. It doesn’t change items position so it is also known as sequence object. List allows duplicate entry so it may have duplicate element. There are 2 general purpose list implementations ArrayList andLinkedList. List interface provides following operations on elements.

• Positional Access: Each element can be accessed by their index position or numerical position so based on their numerical position it manipulates elements in the list. It includes method such as get(), set(), add(), addall() and remove().
• Search: Using IndexOf and lastIndexOf method it searches for specified elements in the list and return their numerical position or index number.
• Iteration: Using listIterator() method traverse lists in a sequential way.
• Range-view: The sublist() method performs arbitrary range operations on the list.

Initialization

A list can be initialized as follow:

List booklist=new ArrayList();

Methods

Programming Example

import java.util.*;
class List_Example
{
 public static void main(String[] args)
 {
   //Creating ArrayList
   List booklist=new ArrayList();
   
   //Adding Item to list
   booklist.add("Java");
   booklist.add("C#");
   booklist.add("C++");
   booklist.add("SQL");
   booklist.add("Python");
   
   //Printing List
   System.out.println(booklist);
   
   //Adding new item at index position 3
   booklist.add(3, "PHP");
   //Printing List
   System.out.println(booklist);
   
   //Getting index position of object SQL
   System.out.println(booklist.indexOf("SQL"));
   
   //Removing Object stored at index position 2
   System.out.println(booklist.remove(2));
   
   //Getting a sublist of object ranging from 2 to 4
   System.out.println(booklist.subList(2,4));
 }
}

Output

Iterator

iterator is an object that implements either Iterator or ListIterator Interface. IteratorInterface allows you to traverse through collections obtaining or removing elements. TheListIterator Interface extends the Iterator and allows you to traverse collection in both direction forward and backward.

Methods and Description of ListIterator

Above is the list of methods that is used while traversing lists using iterators. You can understand its working style more clearly using following programming example.

Programming Example

import java.util.*;
class List_Iterator
{
 public static void main(String[] args)
 {
   //Creating ArrayList
   List booklist=new ArrayList();
   
   //Adding Item to list
   booklist.add("Java");
   booklist.add("C#");
   booklist.add("C++");
   booklist.add("SQL");
   booklist.add("Python");
   
   //Printing List
   System.out.println(booklist);
   
   //Using ListIterator
   //hasNext() Method
   System.out.print("Printing Forward Direction : ");
   ListIterator Ltr=booklist.listIterator();
   while(Ltr.hasNext())
   {
     Object element=Ltr.next();     
     System.out.print(element + " , ");
   }
   System.out.println();
   
   //hasPrevious() Method
   System.out.print("Printing Backward Direction : ");
   while(Ltr.hasPrevious())
   {
     Object element=Ltr.previous();
     System.out.print(element + " , ");
   }
   System.out.println();
 }
}

Output

Summary

In this chapter you have learned how to use List Interface in java collection. You have also learned how to use Iterator and ListIterator Interface to traverse through list. Programming examples help you to understand topic more clearly. In the next chapter you will learn ArrayList class in Java.

In this chapter you will learn:

1. What is Collection in Java?
2. Java Collection Structure
3. List Interface
4. Queue Interface
5. Set Interface
6. Map Interface

Before starting this tutorial you must need to know what Collection in Java is and how to use it in programming. You also need to know the benefit of collection. A collection is like an array which stores collection of data but there is huge difference between them. An array size is fixed and it is defined while initialized array but the size of collection objects is dynamic and can be grow or shrink at run time. There is also various usage of Collection object that is mentioned below:

1. Collection support more flexible data structure than array.
2. The complexity of Collection framework is encapsulated and you are provided several methods and properties to work with them. For example for adding any new element there is add() method. So, it simplifies your code and gives better access to collection element than array.
3. It reduces your development effort by providing rich set of classes.
4. It gives you robust code quality because it is tested by several high qualified programmers.

Structure of Collection

You will learn all the classes and interfaces of collections in next few chapters. All the classes are explained with complete programming examples.

List Interface

A list is an order collections or sequence of items. You can insert, delete or search items based on index position. It also allows duplicate entry in the list collections.

1. ArrayList
2. LinkedList
3. Vector
4. Stack

Queue Interface

A Queue is based on First in First Out formulae. This collection is designed for holding elements prior to processing. Apart from basic collection operations it provides additional insertion, extraction and inspection operations.

1. PriorityQueue
2. Deque
3. ArrayDeque

Set Interface

Unlike List Interface Set doesn’t allow adding duplicate values in collection. It contains method only inherited from collections and prohibited duplicate entries.

1. HashSet
2. LinkedHashSet
3. SortedSet
4. TreeSet

Map Interface

A Map is an object that maps keys to values. It contains unique keys for all the elements and that elements can be accessed later using keys value. A map cannot contain duplicate keys.

1. Hashtable
2. LinkedHashMap
3. HashMap
4. TreeMap

Iterator and ListIterator

Iterator and ListIterator both are used for traversing collections still there are some differences between Iterator and ListIterator. Iterator and listiterator is very useful and we will use it widely in collection programming.

Summary

It is only overview of collections framework. We have kept this topic short and useful but all the interfaces are explained in details in separate chapter. So, let’s start with List Interface