What is the difference between size and capacity of a Vector in Java?

The size of a vector represents the number of components in the vector. The capacity of a vector represents the maximum number of elements the vector can hold.

Example:

import java.util.*;

public class VectorDemo {
   public static void main(String args[]) {
      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.");
      Enumeration vEnum = v.elements();
      System.out.println("\nElements in vector:");
      while(vEnum.hasMoreElements())
      System.out.print(vEnum.nextElement() + " ");
      System.out.println();
   }
}

Output:

Initial size: 0
Initial capacity: 3
Capacity after four additions: 5
Current capacity: 5
Current capacity: 7
Current capacity: 9
First element: 1
Last element: 12
Vector contains 3.
Elements in vector:
1 2 3 4 5.45 6.08 7 9.4 10 11 12