Vectors & Wrapper Classes

Vectors

Vectors class can be used to create a generic dynamic array known as vector that can hold objects of any type and any number. Vector class contained in the java.util.package. The objects do not have to be homogenous. Vectors are created like arrays as follows:

            Vector vect=new vector();       //declaring without size

            Vector vect=new vect(3);                     //declaring with size.

 Vectors possess a number of advantages over arrays:-

1. It is convenient to use vectors to store objects
2. A vector can be used to store a list of objects that may vary in size.
3. We can add and delete objects from the list as and when required.

Vectors can hold only Objects and not primitive types (eg, 5).

Common Vector Methods

There are many useful methods in the Vector class and its parent classes. Here are some of the most useful. v is a Vector, i is an int index, o is an Object.

Method	Description
v.add(o)	adds Object o to Vector v
v.add(i, o)	Inserts Object o at index i, shifting elements up as necessary.
v.clear()	removes all elements from Vector v
v.contains(o)	Returns true if Vector v contains Object o
v.firstElement(i)	Returns the first element.
v.get(i)	Returns the object at int index i.
v.lastElement(i)	Returns the last element.
v.listIterator()	Returns a ListIterator that can be used to go over the Vector. This is a useful alternative to the for loop.
v.remove(i)	Removes the element at position i, and shifts all following elements down.
v.set(i,o)	Sets the element at index i to o.
v.size()	Returns the number of elements in Vector v.
v.toArray(Object[])	The array parameter can be any Object subclass (eg, String). This returns the vector values in that array (or a larger array if necessary). This is useful when you need the generality of a Vector for input, but need the speed of arrays when processing the data.
v.addElement(item)	Adds the item specified to the list at the end
v.elementAt(10)	Gives the name of the 10th object
v.size()	Gives the number of objects present
v.removeElement(item)	Removes the specified item from the list
v.removeElementAt(n)	Removes the item stored in the nth position of the list
v.removeAllElements( )	Removes all the elements in the list
v.copyInto(array)	Copies all items from list to array
v.insertElementAt(item,n)	Inserts the item at nth position

Example Program:

import java.io.*;

import java.util.*;

class VectorDemo1

{

public static void main(String args[]) throws IOException

{

Vector v = new Vector( );

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

while(true)

{

System.out.println("1.Creation");

System.out.println("2.Insertion");

System.out.println("3.Deletion");

System.out.println("4.Display");

System.out.println("5.exit");

System.out.println("Enter Ur Choice:");

int n=Integer.parseInt(br.readLine());

switch(n)

{

            case 1:            

                        System.out.println("Enter the Element:");

                        v.addElement(new Integer(br.readLine()));

                        break;

            case 2: System.out.println("Enter the position to be inserted:");

                        int x=Integer.parseInt(br.readLine());

                        v.insertElementAt(new Integer(br.readLine()),x);

                        break;

            case 3:System.out.println("Enter the position to be deleted:");

                        int y=Integer.parseInt(br.readLine());

                        v.removeElementAt(y);

                        break;

            case 4: System.out.println("Elements are:");

                        for(int i=0;i<v.size();i++)

                        System.out.println(v.get(i)+" ");                      

                        break;

            case 5:System.exit(0);

}

}

}

}

Wrapper Classes

Vectors cannot handle primitive data types like int,float,long,char and double. Primitive data types may be converted into object types by using the wrapper classes contained in Java.lang package.

Following table lists the primitive types and the corresponding wrapper classes:

Primitive	Wrapper
boolean	java.lang.Boolean
byte	java.lang.Byte
char	java.lang.Character
double	java.lang.Double
float	java.lang.Float
int	java.lang.Integer
long	java.lang.Long
short	java.lang.Short