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Java Vector Class

Java Data Structures

The Vector class implements a dynamic array. It is similar to ArrayList, but with two differences:

Vector is primarily used when you do not know the size of the array in advance or you just need an array that can change size.

The Vector class supports 4 types of constructors.

The first constructor creates a default vector with an initial size of 10:

Vector()

The second constructor creates a vector of the specified size:

Vector(int size)

The third constructor creates a vector of the specified size and increment. The increment specifies the number of elements to increase the vector by:

Vector(int size, int incr)

The fourth constructor creates a vector containing the elements of collection c:

Vector(Collection c)

In addition to the methods inherited from its parent class, Vector defines the following methods:

Number Method Description
1 void add(int index, Object element) <br>Inserts the specified element at the specified position in this vector.
2 boolean add(Object o) <br>Appends the specified element to the end of this vector.
3 boolean addAll(Collection c) <br>Appends all of the elements in the specified Collection to the end of this vector, in the order that they are returned by the specified collection's iterator.
4 boolean addAll(int index, Collection c) <br>Inserts all of the elements in the specified Collection into this vector at the specified position.
5 void addElement(Object obj) <br>Adds the specified component to the end of this vector, increasing its size by one.
6 int capacity() <br>Returns the current capacity of this vector.
7 void clear() <br>Removes all of the elements from this vector.
8 Object clone() <br>Returns a clone of this vector.
9 boolean contains(Object elem) <br>Returns true if this vector contains the specified element.
10 boolean containsAll(Collection c) <br>Returns true if this vector contains all of the elements in the specified Collection.
11 void copyInto(Object[] anArray) <br>Copies the components of this vector into the specified array.
12 Object elementAt(int index) <br>Returns the component at the specified index.
13 Enumeration elements() <br>Returns an enumeration of the components of this vector.
14 void ensureCapacity(int minCapacity) <br>Increases the capacity of this vector, if necessary, to ensure that it can hold at least the number of components specified by the minimum capacity argument.
15 boolean equals(Object o) <br>Compares the specified Object with this vector for equality.
16 Object firstElement() <br>Returns the first component (the item at index 0) of this vector.
17 Object get(int index) <br>Returns the element at the specified position in this vector.
18 int hashCode() <br>Returns the hash code value for this vector.
19 int indexOf(Object elem) <br>Returns the index of the first occurrence of the specified element in this vector, or -1 if this vector does not contain the element.
20 int indexOf(Object elem, int index) <br>Returns the index of the first occurrence of the specified element in this vector, searching forwards from index, or returns -1 if the element is not found.
21 void insertElementAt(Object obj, int index) <br>Inserts the specified object as a component in this vector at the specified index.
22 boolean isEmpty() <br>Tests if this vector has no components.
23 Object lastElement() <br>Returns the last component of the vector.
24 int lastIndexOf(Object elem) <br>Returns the index of the last occurrence of the specified element in this vector, or -1 if this vector does not contain the element.
25 int lastIndexOf(Object elem, int index) <br>Returns the index of the last occurrence of the specified element in this vector, searching backwards from index, or returns -1 if the element is not found.
26 Object remove(int index) <br>Removes the element at the specified position in this vector.
27 boolean remove(Object o) <br>Removes the first occurrence of the specified element in this vector, if it is present. If the vector does not contain the element, it is unchanged.
28 boolean removeAll(Collection c) <br>Removes from this vector all of its elements that are contained in the specified Collection.
29 void removeAllElements() <br>Removes all components from this vector and sets its size to zero.
30 boolean removeElement(Object obj) <br>Removes the first (lowest-indexed) occurrence of the argument from this vector.
31 void removeElementAt(int index) <br>Deletes the component at the specified index.
32 protected void removeRange(int fromIndex, int toIndex) <br>Removes from this List all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
33 boolean retainAll(Collection c) <br>Retains only the elements in this vector that are contained in the specified Collection.
34 Object set(int index, Object element) <br>Replaces the element at the specified position in this vector with the specified element.
35 void setElementAt(Object obj, int index) <br>Sets the component at the specified index of this vector to be the specified object.
36 void setSize(int newSize) <br>Sets the size of this vector.
37 int size() <br>Returns the number of components in this vector.
38 List subList(int fromIndex, int toIndex) <br>Returns a view of the portion of this List between fromIndex, inclusive, and toIndex, exclusive.
39 Object[] toArray() <br>Returns an array containing all of the elements in this vector in the correct order.
40 Object[] toArray(Object[] a) <br>Returns an array containing all of the elements in this vector in the correct order; the runtime type of the returned array is that of the specified array.
41 String toString() <br>Returns a string representation of this vector, containing the String representation of each element.
42 void trimToSize() <br>Trims the capacity of this vector to be the vector's current size.

Example

The following program illustrates several of the methods supported by this collection:

import java.util.*;

public 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();
   }
}
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();
}
}

The above example compiles and runs with the following results:

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

Java Data Structures

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