[Solixious]

Java vectors have a big advantage over the array data structure since it is very flexible and its size can be increased or decreased very easily.

Importing Vector
Vectors are a part of java.util package so you need to import it before using it.

Code:

import java.util.Vector;

Creating a new Vector
One following constructors are to be used to create a Vector.

Code:

public Vector()
public Vector(int size)
public Vector(int size,int incr)
public Vector(Collection c)

Example :

Code:

Vector v=new Vector(5,3);

This will create a new Vector that has a size of 5 i.e. it can store 5 pieces of information. If you try to store a sixth piece, it will automatically re-size to 8 (5+3). If you add nine, it'll re-size to 12, and so on.

Adding Elements to a Vector

The two basic ways of adding elements to a vector is by using the following methods

Code:

public boolean add (Object o)
public void add (int index, Object o)

The first function appends the element to the end of the vector while the second element adds the element at specific position while resizing the Vector and shifting the remaining elements.
Example :

Code:

v.add("Hack Community");
v.add(2,"HC");

Removing Elements from a Vector

Removing element(s) from a Vector is very simple. The methods to be used are as follows :

Code:

public Object remove(int index)

The above method will remove the element from the specified index and return the value of the element that was removed. After removing the element, it will shift the remaining elements to fill up the voids.

Code:

public void remove(Object element)

The above method will search the entire vector for the element passed as argument, remove its first occurrence, and shift the remaining elements to fill the void created in Vector.

Code:

void removeRange(int lowerbound,int upperbound)

It will remove all the elements within the given lower bound and upper bound indexes and shift the remaining values respectively.
Example :

Code:

String s=v.remove(2);
v.remove("Hack Community");
v.remove(3,10);

Reading the Elements in a Vector
Use the following methods to get the elements stored in a Vector

Code:

Object firstElement()
Object lastElement()
Object get(int index)

Use the first method to get the element stored at index 0. The second method is used to return the last object of the vector. The other method can be used to retrieve elements from any index in the Vector.
Example :

Code:

String first=v.firstElement();
String fourth=v,get(3);

Check if a Vector is empty or not
Following is the method to check if the Vector is empty or not.

Code:

boolean isEmpty()

Example :

Code:

if(v.isEmpty())
  {
  System.out.println("The Vector is empty.");
  }
else
  {
  System.out.println("The Vector is not empty");
  }

Some more useful methods of Vector class

Code:

int indexOf(Object element)

The above function returns the index of first occurrence of the element passed as parameter.

Code:

int indexOf(Object element,int index)

The above function returns the index of first occurrence of the element passed as parameter beginning the search from the index passed as second parameter.

Code:

int lastIndexOf(Object element)

The above function returns the index of last occurrence of the element passed as parameter. That means the search starts at the end point of the vector and goes backward.

Code:

int lastIndexOf(Object element,int index)

The above function searches backwards for the specified object, starting from the specified index, and returns an index to it.

Code:

void setSize(int newSize)

It re-sizes the vector to a new size passed as its parameter.

Code:

String toString()

Returns a string representation of this Vector, containing the String representation of each element.

Code:

void clear()

Removes all of the elements from this Vector.

A Sample Program

Code:

import java.util.*;
class VectorDemo {
   public static void main(String args[]) {
      // initial size is 3, increment is 2
      Vector v = new Vector(3, 2);
      System.out.println("Initial size: " + v.size());
      System.out.println("Initial capacity: " +
      v.capacity());
      v.addElement(new Integer(1));
      v.addElement(new Integer(2));
      v.addElement(new Integer(3));
      v.addElement(new Integer(4));
      System.out.println("Capacity after four additions: " +
          v.capacity());

      v.addElement(new Double(5.45));
      System.out.println("Current capacity: " +
      v.capacity());
      v.addElement(new Double(6.08));
      v.addElement(new Integer(7));
      System.out.println("Current capacity: " +
      v.capacity());
      v.addElement(new Float(9.4));
      v.addElement(new Integer(10));
      System.out.println("Current capacity: " +
      v.capacity());
      v.addElement(new Integer(11));
      v.addElement(new Integer(12));
      System.out.println("First element: " +
         (Integer)v.firstElement());
      System.out.println("Last element: " +
         (Integer)v.lastElement());
      if(v.contains(new Integer(3)))
         System.out.println("Vector contains 3.");
      // enumerate the elements in the vector.
      Enumeration vEnum = v.elements();
      System.out.println("\nElements in vector:");
      while(vEnum.hasMoreElements())
         System.out.print(vEnum.nextElement() + " ");
      System.out.println();
   }
}
//Source : Java Examples

That brings an end to this tutorial of using Vectors in Java.

[Deque]

The real value here lies in the example code, because the information about the methods you get by reading the API (which every programmer should do).

Some additional information: Most of the time the ArrayList will be more suitable, unless you need synchronization. Expecially beginners won't deal with threads. The ArrayList is almost the same, just that it is not synchronized (therefor faster) and the ArrayList increases its size by 50%, whereas the Vectors default doubles its size when the underlying array is full.

[Shining White]

i remember i had a exam call SCJP / OCJP