Vectors in Java are one of the most commonly used data structures in the programming world. We all know that Arrays are data structures that hold the data in a linear fashion. Vectors also store the data in a linear fashion, but unlike Arrays, they do not have a fixed size. Instead, their size can be increased on demand.

Vector class is a child class of AbstractList class and implements on List interface. To use Vectors, we first have to import Vector class from java.util package: import java.util.Vector

Vectors Constructors

Listed below are the multiple variations of vector constructors available to use:

1. Vector(int initialCapacity, int Increment)-Constructs a vector with given initialCapacity and its Increment in size.
2. Vector(int initialCapacity)-Constructs an empty vector with given initialCapacity. In this case, Increment is zero.
3. Vector()-Constructs a default vector of capacity 10.
4. Vector(Collection c)-Constructs a vector with a given collection, the order of the elements is same as returned by the collection’s iterator.

There are also three protected parameters in vectors

1. Int capacityIncrement()- It automatically increases the capacity of the vector when the size becomes greater than capacity.
2. Int elementCount()-tell number of elements in the vector
3. Object[] elementData()-array in which elements of vector are stored

Advantages of Vector in Java

• The property of having a dynamic size is very much useful as it avoids the memory wastage in case we do not know the size of the data-Structures at the time of declaration.
• When we want to change the size of our data structure in the middle of a program, vectors can prove to be very useful.

The property of having a dynamic size is not unique to Vectors in Java. Another data structure, known as ArrayList also shows the property of having a dynamic size. However, Vectors are different from ArrayLists due to a couple of reasons:

• First, Vectors are synchronized which gives it an advantage over ArrayList as compared to multi-threaded programs as there are risks of data corruption.
• Secondly, Vectors have some legacy functions which can be implemented only on vectors and not on ArrayLists.

Example: Initializing Vector Constructors

// Java code illustrating Vector Constructors

import java.util.*;

public class Main{

public static void main(String[] args)

{

// create default vector

Vector v1 = new Vector();

// create a vector of given Size

Vector v2 = new Vector(20);

// create a vector of given Size and Increment

Vector v3 = new Vector(30,10);

v2.add(100);

v2.add(100);

v2.add(100);

// create a vector with given collection

Vector v4 = new Vector(v2);

System.out.println("Vector v1 of capacity " + v1.capacity());

System.out.println("Vector v2 of capacity " + v2.capacity());

System.out.println("Vector v3 of capacity " + v3.capacity());

System.out.println("Vector v4 of capacity " + v4.capacity());

}

Methods in Vector

Let’s have a look at few very frequently used vector methods.

• Boolean add(Object o) — It appends an element at the end of the vector.
• Void add (int Index, E element) — It adds the given element at the specified index in the vector.
• Boolean Remove(object o) — It removes remove the element at the given index in the vector.
• Boolean removeElement(Object obj) — It deletes the element by its name obj (not by index number).
• Int size() — It returns the size of the vector.
• Int Capacity() — It returns the capacity of the vector.
• Object get(int index) — It returns the element at the given position in the vector.
• Object firstElement() — It returns the first element.
• Object lastElement() — It returns the last element.
• Boolean equals(Object o) — It compares the vector with the specified object for equality. It returns true if all elements are true at their corresponding places.
• Void trimtosize() — This method removes extra capacity and keeps the capacity just to hold the elements i.e. equal to the size.