Java Vector class

The java.util.Vector class is a legacy class in the Collections framework. It basically implements a growable array of objects. Vector extends AbstractList class and implements List Interface.

It is similar to ArrayList class, but with two differences −

1. It is rarely used in non-threaded environment as it is synchronized and due to which it gives poor performance in terms of search, addition, deletion and updation operations on its elements.

2. It contains many legacy methods that are not part of the Java Collections Framework.

Vector proves to be very useful if we don’t know the size of the array in advance or we just need one collection that can change its size dynamically over the lifespan of a program.

Vector Class Constructors

Following is the list of constructors provided by the Java Vector class.

Vector Class Methods

Apart from the methods inherited from its super classes and super interfaces, Vector defines the following methods −

Besides these, Vector class defines three protected data members:

• int capacityIncreament: It indicates the amount by which the capacity of the Vector is automatically incremented when its size becomes greater than its capacity.
• int elementCount: It denotes the number number of valid components in this Vector object.
• Object elementData[ ]: It indicates the array buffer into which the components of the Vector are stored.

Example 1

The following example shows the use of different constructors of Vector class. It also demonstrates that if increment is specified, Vector will expand according to it in each allocation cycle but if increment is not specified then vector’s capacity get doubled in each allocation cycle. Methods like size(), capacity() and add() are also used here.

VectorDemo1.java

import java.util.Vector;

public class VectorDemo1 {

    public static void main(String[] args) {
        // Use of constructor 1        
        Vector v1 = new Vector(); 
        for (int i = 10; i <= 90; i = i + 10) {
            v1.add(new Integer(i));
        }
        System.out.println("Vector1 = " + v1);
        System.out.println("Size = " + v1.size());
        System.out.println("Capacity = " + v1.capacity());
        System.out.println();
        
        // Use of constructor 2 
        Vector v2 = new Vector(8); 
        for (double i = 11.11; i <= 99.99; i = i + 11.11) {
            v2.add(i); //autoboxing: "add(i)" is equivalent to "new Double(i)"
        }
        System.out.println("Vector2 = " + v2);
        System.out.println("Size = " + v2.size());
        System.out.println("Capacity = " + v2.capacity());
        System.out.println();
        
        // Use of constructor 3 
        Vector v3 = new Vector(5, 3); 
        for (int i = 11; i <= 99; i = i + 11) {
            v3.add(i); //autoboxing: "add(i)" is equivalent to "new Integer(i)"
        }
        System.out.println("Vector3 = " + v3);
        System.out.println("Size = " + v3.size());
        System.out.println("Capacity = " + v3.capacity());
        System.out.println();
        
        // Vector object created using Generics concept
        Vector<String> list = new Vector<String>();
        list.add("hello");
        list.add("hi");
        list.add("bye");
        
        // Use of constructor 4
        Vector v4 = new Vector(list);
        System.out.println("Vector4 = " + v4);
        System.out.println("Size = " + v4.size());
        System.out.println("Capacity = " + v4.capacity());
        v4.add("thanks");
        v4.add("welcome");
        System.out.println("Vector4 modified = " + v4);
        System.out.println("Size = " + v4.size());
        System.out.println("Capacity = " + v4.capacity());
        System.out.println();
    }
}

Output:

Vector1 = [10, 20, 30, 40, 50, 60, 70, 80, 90]
Size = 9
Capacity = 10

Vector2 = [11.11, 22.22, 33.33, 44.44, 55.55, 66.66, 77.77, 88.88, 99.99]
Size = 9
Capacity = 16

Vector3 = [11, 22, 33, 44, 55, 66, 77, 88, 99]
Size = 9
Capacity = 11

Vector4 = [hello, hi, bye]
Size = 3
Capacity = 3
Vector4 modified = [hello, hi, bye, thanks, welcome]
Size = 5
Capacity = 6

Example 2

The following example demonstrates the use of different methods of Vector class mainly for addition or insertion operations. It also shows how to enumerate and iterate through the different elements of Vector.

VectorDemo2.java

import java.util.Enumeration;
import java.util.Iterator;
import java.util.Vector;

public class VectorDemo2 {

    public static void main(String[] args) {
        // Creating a Vector of diffrent data types
        Vector v = new Vector();
        System.out.println("Vector = " + v);
        System.out.println("Size = " + v.size());
        System.out.println("Capacity = " + v.capacity());

        for (int i = 1; i < 10; i++) {
            v.add(new Integer(i * 11)); //same as v.add(i*11)
        }
        v.add("ASIA");
        System.out.println("\nVector = " + v);
        System.out.println("Size = " + v.size());
        System.out.println("Capacity = " + v.capacity());

        v.add(0, new Double(99.99)); //same as v.add(0, 99.99)
        v.addElement("AUSTRALIA");
        v.insertElementAt("EUROPE", 11);
        System.out.println("\nVector = " + v);
        System.out.println("Size = " + v.size());
        System.out.println("Capacity = " + v.capacity());

        Object arr[] = v.toArray();
        // Accessing elements of the Object array
        System.out.println("\nObject array elements are : ");
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println("\n");

        System.out.println("Vector = " + v);
        System.out.println("Size = " + v.size());
        System.out.println("Capacity = " + v.capacity());

        // Accessing elements of Vector using get() method
        System.out.println("\nVector elements are : ");
        for (int i = 0; i < v.size(); i++) {
            System.out.print(v.get(i) + " ");
        }
        System.out.println();

        System.out.println("\nVector elements are : ");
        // Iterate through the elements of Vector
        Iterator it = v.iterator();
        while (it.hasNext()) {
            System.out.print(it.next() + " ");
        }
        System.out.println();

        System.out.println("\nVector elements are : ");
        // Enumerate through the elements of Vector
        Enumeration e = v.elements();
        while (e.hasMoreElements()) {
            System.out.print(e.nextElement() + " ");
        }
        System.out.println();

        // Remove all elements of Vector
        v.removeAll(v);
        System.out.println("\nVector = " + v);
        System.out.println("Size = " + v.size());
        System.out.println("Capacity = " + v.capacity());
    }
}

Output:

Vector = []
Size = 0
Capacity = 10

Vector = [11, 22, 33, 44, 55, 66, 77, 88, 99, ASIA]
Size = 10
Capacity = 10

Vector = [99.99, 11, 22, 33, 44, 55, 66, 77, 88, 99, ASIA, EUROPE, AUSTRALIA]
Size = 13
Capacity = 20

Object array elements are : 
99.99 11 22 33 44 55 66 77 88 99 ASIA EUROPE AUSTRALIA

Vector = [99.99, 11, 22, 33, 44, 55, 66, 77, 88, 99, ASIA, EUROPE, AUSTRALIA]
Size = 13
Capacity = 20

Vector elements are : 
99.99 11 22 33 44 55 66 77 88 99 ASIA EUROPE AUSTRALIA

Vector elements are : 
99.99 11 22 33 44 55 66 77 88 99 ASIA EUROPE AUSTRALIA

Vector elements are : 
99.99 11 22 33 44 55 66 77 88 99 ASIA EUROPE AUSTRALIA

Vector = []
Size = 0
Capacity = 20

Example 3

The following example demonstrates the use of different methods of Vector class mainly for deletion or removal operations. It also shows how to use the ensureCapacity() method of Vector.

VectorDemo3.java

import java.util.Vector;

public class VectorDemo3 {

    public static void main(String[] args) {
        // Creating a Vector of type String using Java SE 8 style
        Vector<String> list = new Vector<>();
        
        // Adding elements to the Vector
        list.add("JAVA");
        list.add("IS");
        list.add("THE");
        list.add("BEST");
        list.add("LANGUAGE");
        list.add(4, "PROGRAMMING");
        System.out.println("Vector = " + list);
        System.out.println("Size = " + list.size());
        System.out.println("Capacity = " + list.capacity());
        
        // Ensuring capacity 
        list.ensureCapacity(25); 
        System.out.println("\nNew Capacity = " + list.capacity());

        // Copying Vector elements using copyInto() method
        Object obj[] = new Object[list.size()];
        list.copyInto(obj);
        System.out.println("\nElements from Object array: ");
        System.out.println("==========================");
        for (int i = 0; i < obj.length; i++) {
            System.out.print(obj[i] + " ");
        }
        System.out.println();
        
        // Copying Vector elements using toArray() method
        String[] strObj = new String[list.size()]; 
        strObj = (String[])list.toArray(strObj); 
        System.out.println("\nElements from String array: ");
        System.out.println("==========================");
        list.forEach(System.out::println);
        
        if (list.contains("BEST")) {
            System.out.println("\nBEST is present at the index " + list.indexOf("BEST"));
        } 
        else {
            System.out.println("\nBEST is not present in the list.");
        }
        
        // Get the first element  
        System.out.println("\nThe first elementl of vector is = " + list.firstElement());
        // Get the last element  
        System.out.println("\nThe last lement of vector is = " + list.lastElement());
        
        // Using remove()
        String element = list.remove(4);
        System.out.println("\nRemoved Element: " + element);
        System.out.println("Vector after remove(): " + list);
        
        // Remove an element 
        list.removeElement("IS"); 
        System.out.println("\nVector after removeElement(): " + list);
        
        // Using clear()
        list.clear();
        System.out.println("\nVector after clear(): " + list);
    }
}

Output:

Vector = [JAVA, IS, THE, BEST, PROGRAMMING, LANGUAGE]
Size = 6
Capacity = 10

New Capacity = 25

Elements from Object array: 
==========================
JAVA IS THE BEST PROGRAMMING LANGUAGE

Elements from String array: 
==========================
JAVA
IS
THE
BEST
PROGRAMMING
LANGUAGE

BEST is present at the index 3

The first elementl of vector is = JAVA

The last lement of vector is = LANGUAGE

Removed Element: PROGRAMMING
Vector after remove(): [JAVA, IS, THE, BEST, LANGUAGE]

Vector after removeElement(): [JAVA, THE, BEST, LANGUAGE]

Vector after clear(): []