Vector in Java

The Vector in Java is a class that implements a dynamic array. This means we can increase or decrease the size of the array dynamically. It is same like ArrayList in Java but has few differences. In this tutorial, we will understand in detail the Java Vector class, its implementation, and different methods.

Java Vector

The Java Vector class implements the List interface and is part of the legacy classes which means it has its own methods that are not present in the Collection framework. The Java vector class is present in the java.util package. Hence to use the vector class, we need to import the java.util.Vector package.

Java Vector is used to create an array of dynamic size. This means we can increment the size of the array we add the elements after it reaches a specific size. We will understand in detail about this in the next section.

Another feature of the vector is that we can store values of different data types to the same vector object. Suppose we have created a vector object, we can add an integer value first, then a string value, then again an integer, and so on.

Java Vector Constructors

We can declare vector in the below different ways:

Java Vector Methods

We can use the below methods or operations for a vector class:

Example: Different ways to create a vector

Below is an example that shows the different ways of creating a vector using its constructors.

import java.util.Vector;

public class VectorDemo {

  public static void main(String[] args) {
    Vector<Integer> v1 = new Vector<Integer>();
    
    //Adding elements
    v1.add(2);
    v1.add(3);
    
    Vector<String> v2 = new Vector<String>(3);
    Vector<String> v3 = new Vector<String>(4,2);
    Vector<Integer> v4 = new Vector<Integer>(v1);
    
    //Capacity of each vector
    System.out.println("Capacity of v1: " + v1.capacity());
    System.out.println("Capacity of v2: " + v2.capacity());
    System.out.println("Capacity of v3: " + v3.capacity());
    System.out.println("Capacity of v4: " + v4.capacity());

    v3.add("Java");
    v3.add("C");
    v3.add("C++");
    v3.add("Python");
    v3.add("Ruby");
    System.out.println("Capacity of v3 after adding elements: " + v3.capacity());
  }

}

Capacity of v1: 10
Capacity of v2: 3
Capacity of v3: 4
Capacity of v4: 2
Capacity of v3 after adding elements: 6

Example: Add different data types to a vector

Below is an example to show how a vector can contain different data type values. Here we store data types of both Integer and String in the same vector object.

import java.util.Vector;

public class VectorDemo {

  public static void main(String[] args) {
    Vector v = new Vector();
    v.add("Java");
    v.add(100);
    v.add("Language");
    System.out.println(v);
  }

}

[Java, 100, Language]

Example: Add Elements to Vector

The below example shows different ways to add elements to a vector in Java. Using the add() method, we can individual elements in sequential order. The add(element, index) method adds the element at the specified index. The addElement() method adds the element at the end. We can use the addAll(c) method to add a collection of elements.

import java.util.Vector;

public class VectorAddElements {

  public static void main(String[] args) {
    Vector<Integer> num = new Vector<Integer>();
    num.add(10);
    num.add(20);
    System.out.println("List of elements: " + num);
    
    //Add element at specified index
    num.add(1, 15);
    System.out.println("List of elements: " + num);
    
    //Add an element
    num.addElement(25);
    System.out.println("List of elements: " + num);
    
    Vector<Integer> n = new Vector<Integer>();
    n.add(30);
    n.add(35);
    
    //Add a collection to the vector
    num.addAll(3, n);

    System.out.println("List of elements: " + num);
  }

}

List of elements: [10, 20]
List of elements: [10, 15, 20]
List of elements: [10, 15, 20, 25]
List of elements: [10, 15, 20, 30, 35, 25]

Example: Remove elements from the vector

The below example shows different ways to remove elements from the vector. The remove(index) and removeElementAt(index) removes the element at the specified index. We use remove(element) and removeElement(element) to remove the specified element. The removeAllElements() removes all the elements from the vector and empties the vector.

import java.util.Vector;
public class VectorRemoveElements {

  public static void main(String[] args) {
    Vector<String> names = new Vector<String>();
    names.add("Ramya");
    names.add("Kavitha");
    names.add("Sunitha");
    names.add("Devika");
    names.add("Radhika");
    
    System.out.println("Vector elements: " + names);
    
    names.remove(1);
    System.out.println("Elements after removing element at index 1: " + names);
    names.remove("Sunitha");
    System.out.println("Elements after removing the specified element: " + names);
    
    Vector<String> n = new Vector<String>();
    n.add("Ram");
    n.add("Dev");
    n.add("Das");
    n.add("Jay");
    
    names.addAll(n);
    System.out.println("Elements after adding collection: " + names);
    names.removeElement("Dev");
    System.out.println("Elements after removing specified element: " + names);
    names.removeAll(n);
    System.out.println("Elements after removing the collection: " + names);
    names.removeElementAt(1);
    System.out.println("Elements after removing the element at the specified index: " + names);
    names.removeAllElements();
    System.out.println("Elements after removing all elements: " + names);
    System.out.println("Is vector empty: " + names.isEmpty());

  }

}

Vector elements: [Ramya, Kavitha, Sunitha, Devika, Radhika]
Elements after removing element at index 1: [Ramya, Sunitha, Devika, Radhika]
Elements after removing the specified element: [Ramya, Devika, Radhika]
Elements after adding collection: [Ramya, Devika, Radhika, Ram, Dev, Das, Jay]
Elements after removing specified element: [Ramya, Devika, Radhika, Ram, Das, Jay]
Elements after removing the collection: [Ramya, Devika, Radhika]
Elements after removing the element at the specified index: [Ramya, Radhika]
Elements after removing all elements: []
Is vector empty: true

Example: Update and Retrieve elements from a vector

There are different ways to retrieve elements from a vector in Java and its corresponding index. The below example shows how to update the value and retrieve various elements from the vector. We can update the element using the set() method or setElementAt() method.

The elementAt() and get() is used to retrieve the element at the specified index. We use firstElement() to get the first element and lastElement() to get the last element in the vector.

import java.util.Vector;
public class RetrieveVectorElements {

  public static void main(String[] args) {
    Vector v = new Vector();
    v.add("Welcome");
    v.add("to");
    v.add("Java");
    v.add("programming");
    v.add(100);
    
    System.out.println("Vector content:" + v);
    System.out.println("Element at index 2: " + v.elementAt(2));
    System.out.println("First element: " + v.firstElement());
    System.out.println("Element at index 3: " + v.get(3));
    System.out.println("Index of the specified element: " + v.indexOf("Java"));
    System.out.println("Index of the element from the specified index: " + v.indexOf(100, 1));
    System.out.println("Last element: " + v.lastElement());
    System.out.println("Last index of the element: " + v.lastIndexOf("programming"));
    System.out.println("Last index of the element from the specified index: " + v.lastIndexOf("to", 3));
 
    v.set(4,"language");
    v.setElementAt("Python", 2);
    System.out.println("Elements after using set method: " + v);
    
  }

}

Vector content:[Welcome, to, Java, programming, 100]
Element at index 2: Java
First element: Welcome
Element at index 3: programming
Index of the specified element: 2
Index of the element from the specified index: 4
Last element: 100
Last index of the element: 3
Last index of the element from the specified index: 1
Elements after using set method: [Welcome, to, Python, programming, language]

Example: Iterate through elements in a vector

We can iterate through elements in the vector using below different ways:

• For loop
• Enhanced for loop
• Iterator
• List Iterator

Below example shows how to traverse through the vector using all the above methods.

import java.util.Iterator;
import java.util.ListIterator;
import java.util.Vector;
public class IterateVectorElements {

  public static void main(String[] args) {
    Vector<String> cities = new Vector<String>();
    cities.add("Chennai");
    cities.add("Delhi");
    cities.add("Bangalore");
    cities.add("Hyderabad");
    
    //For loop
    System.out.println("Iteration through for loop");
    for(int i=0;i<cities.size();i++)
      System.out.println(cities.get(i));
    
    //Enhance for loop
    System.out.println("Iteration through enhanced for loop");
    for(String c: cities)
      System.out.println(c);
    
    //Iterator
    System.out.println("Iteration through iterator");
    Iterator<String> it = cities.iterator();
    it.forEachRemaining(System.out::println);
    
    //ListIterator
    System.out.println("Iteration through List Iterator");
    ListIterator<String> lit = cities.listIterator();
    lit.forEachRemaining(System.out::println);

  }

}

Iteration through for loop
Chennai
Delhi
Bangalore
Hyderabad
Iteration through enhanced for loop
Chennai
Delhi
Bangalore
Hyderabad
Iteration through iterator
Chennai
Delhi
Bangalore
Hyderabad
Iteration through List Iterator
Chennai
Delhi
Bangalore
Hyderabad

Example: Empty elements in Vector

In the below example, we can see how to empty the vector using the clear() method. We can also use removeAllElements() method as we saw in the previous example.

import java.util.Iterator;
import java.util.ListIterator;
import java.util.Vector;
public class IterateVectorElements {

  public static void main(String[] args) {
    Vector<String> cities = new Vector<String>();
    cities.add("Chennai");
    cities.add("Delhi");
    cities.add("Bangalore");
    cities.add("Hyderabad");
    
    cities.clear();
    System.out.println("Is vector empty: " + cities.isEmpty());

  }

}

Is vector empty: true

Reference