🧭 Vectors in Java 

In Java, when we need to store a dynamic list of elements (that can grow or shrink during runtime), we use the Vector class.

Before modern collections like ArrayList were introduced, Vector was widely used to store dynamic data. Even today, it remains important for understanding the evolution of Java’s Collection Framework.

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🔹 What is a Vector?

A Vector in Java is a resizable array that can store elements of the same type.
Unlike regular arrays that have a fixed size, vectors automatically increase their capacity when more elements are added.

Vectors belong to the package:

java.util

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🔹 Key Features of Vectors

✅ Can grow or shrink dynamically
✅ Can store duplicate elements
✅ Maintains insertion order
✅ Synchronized — thread-safe (unlike ArrayList)
✅ Provides many useful built-in methods for easy manipulation

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🔹 Syntax to Create a Vector

Vector<Type> vectorName = new Vector<Type>();

Example:

import java.util.Vector;

public class Example {
    public static void main(String[] args) {
        Vector<Integer> numbers = new Vector<Integer>();
    }
}

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🔹 Adding Elements to a Vector

You can use the add() method to insert elements.

import java.util.Vector;

public class AddExample {
    public static void main(String[] args) {
        Vector<String> fruits = new Vector<String>();

        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        System.out.println("Fruits: " + fruits);
    }
}

Output:

Fruits: [Apple, Banana, Cherry]

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🔹 Accessing Elements in a Vector

You can access elements using the get(index) method or an iterator.

System.out.println(fruits.get(1)); // prints Banana

Or using a loop:

for (int i = 0; i < fruits.size(); i++) {
    System.out.println(fruits.get(i));
}

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🔹 Updating and Removing Elements

Update an element:

fruits.set(1, "Blueberry");
System.out.println(fruits);

Output:

[Apple, Blueberry, Cherry]

Remove an element:

fruits.remove(2);
System.out.println(fruits);

Output:

[Apple, Blueberry]

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🔹 Example 1: Basic Vector Operations

import java.util.Vector;

public class VectorExample {
    public static void main(String[] args) {
        Vector<Integer> numbers = new Vector<Integer>();

        // adding elements
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(40);

        System.out.println("Initial Vector: " + numbers);

        // accessing elements
        System.out.println("First element: " + numbers.get(0));

        // updating element
        numbers.set(2, 99);
        System.out.println("After update: " + numbers);

        // removing element
        numbers.remove(1);
        System.out.println("After removal: " + numbers);
    }
}

Output:

Initial Vector: [10, 20, 30, 40]
First element: 10
After update: [10, 20, 99, 40]
After removal: [10, 99, 40]

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🔹 Iterating Through a Vector

You can traverse a Vector using:

1️⃣ For Loop

for (int i = 0; i < numbers.size(); i++) {
    System.out.println(numbers.get(i));
}

2️⃣ Enhanced For Loop (For-Each)

for (int num : numbers) {
    System.out.println(num);
}

3️⃣ Iterator

import java.util.Iterator;

Iterator<Integer> it = numbers.iterator();
while (it.hasNext()) {
    System.out.println(it.next());
}

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🔹 Vector Methods at a Glance

Method	Description	Example
add(element)	Adds element at the end	v.add(10)
add(index, element)	Inserts element at specific position	v.add(1, 25)
get(index)	Returns element at index	v.get(2)
set(index, element)	Replaces element	v.set(0, 99)
remove(index)	Removes element at index	v.remove(1)
clear()	Removes all elements	v.clear()
size()	Returns number of elements	v.size()
contains(value)	Checks if element exists	v.contains(30)
isEmpty()	Checks if vector is empty	v.isEmpty()
firstElement()	Returns first element	v.firstElement()
lastElement()	Returns last element	v.lastElement()
capacity()	Returns current capacity	v.capacity()

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🔹 Example 2: Using Vector Methods

import java.util.Vector;

public class VectorMethods {
    public static void main(String[] args) {
        Vector<String> animals = new Vector<String>();

        animals.add("Dog");
        animals.add("Cat");
        animals.add("Elephant");
        animals.add("Tiger");

        System.out.println("Animals: " + animals);
        System.out.println("First: " + animals.firstElement());
        System.out.println("Last: " + animals.lastElement());
        System.out.println("Contains Cat? " + animals.contains("Cat"));
        System.out.println("Size: " + animals.size());
        System.out.println("Capacity: " + animals.capacity());
    }
}

Output:

Animals: [Dog, Cat, Elephant, Tiger]
First: Dog
Last: Tiger
Contains Cat? true
Size: 4
Capacity: 10

(By default, a Vector starts with a capacity of 10 and doubles when full.)

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🔹 Vector vs ArrayList

Feature	Vector	ArrayList
Synchronization	✅ Synchronized (Thread-safe)	❌ Not synchronized
Performance	⚙️ Slower (because of synchronization)	⚡ Faster
Growth	Doubles its size	Increases by 50%
Introduced in	JDK 1.0 (Legacy class)	JDK 1.2
Use Case	Multi-threaded programs	Single-threaded programs

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🔹 Example 3: Copy All Elements from One Vector to Another

import java.util.Vector;

public class CopyVector {
    public static void main(String[] args) {
        Vector<Integer> v1 = new Vector<Integer>();
        v1.add(1);
        v1.add(2);
        v1.add(3);

        Vector<Integer> v2 = new Vector<Integer>();
        v2.addAll(v1);

        System.out.println("Vector 1: " + v1);
        System.out.println("Vector 2: " + v2);
    }
}

Output:

Vector 1: [1, 2, 3]
Vector 2: [1, 2, 3]

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🔹 Example 4: Removing All Elements from a Vector

import java.util.Vector;

public class ClearVector {
    public static void main(String[] args) {
        Vector<String> colors = new Vector<String>();
        colors.add("Red");
        colors.add("Blue");
        colors.add("Green");

        System.out.println("Before clear: " + colors);

        colors.clear();

        System.out.println("After clear: " + colors);
    }
}

Output:

Before clear: [Red, Blue, Green]
After clear: []

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💡 Summary

Concept	Description
Vector	Dynamic array from java.util package
Resizable	Grows automatically as elements are added
Thread-safe	Synchronized, safe for multi-threading
Common methods	add(), get(), set(), remove(), size(), capacity()
Alternative	ArrayList — faster but not synchronized

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🧾 Key Takeaway

Vectors are an important part of Java’s legacy collection classes.
Even though ArrayList is more commonly used today, understanding Vector helps build a solid foundation for Java Collection Framework concepts like synchronization and dynamic storage.

Example Programs

 1️⃣ Program to Store and Print 5 Student Names using a Vector

import java.util.Vector;

public class StudentNames {
    public static void main(String[] args) {
        // Create a Vector to store student names
        Vector<String> students = new Vector<String>();

        // Add 5 student names
        students.add("Asha");
        students.add("Rahul");
        students.add("Neha");
        students.add("Vishal");
        students.add("Anu");

        // Display all student names
        System.out.println("List of Students:");
        for (String name : students) {
            System.out.println(name);
        }
    }
}

Output:

List of Students:
Asha
Rahul
Neha
Vishal
Anu

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 2️⃣ Program to Remove Duplicate Elements from a Vector

import java.util.Vector;

public class RemoveDuplicates {
    public static void main(String[] args) {
        Vector<Integer> numbers = new Vector<Integer>();

        // Adding elements (with duplicates)
        numbers.add(10);
        numbers.add(20);
        numbers.add(10);
        numbers.add(30);
        numbers.add(20);

        System.out.println("Original Vector: " + numbers);

        // Remove duplicates manually
        Vector<Integer> unique = new Vector<Integer>();
        for (Integer n : numbers) {
            if (!unique.contains(n)) {
                unique.add(n);
            }
        }

        System.out.println("After removing duplicates: " + unique);
    }
}

Output:

Original Vector: [10, 20, 10, 30, 20]
After removing duplicates: [10, 20, 30]

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3️⃣ Create a Vector of Integers and Find the Largest Element

import java.util.Vector;

public class LargestElement {
    public static void main(String[] args) {
        Vector<Integer> numbers = new Vector<Integer>();

        numbers.add(25);
        numbers.add(10);
        numbers.add(67);
        numbers.add(42);
        numbers.add(39);

        System.out.println("Vector elements: " + numbers);

        // Assume first element is largest initially
        int largest = numbers.get(0);

        for (int i = 1; i < numbers.size(); i++) {
            if (numbers.get(i) > largest) {
                largest = numbers.get(i);
            }
        }

        System.out.println("Largest element: " + largest);
    }
}

Output:

Vector elements: [25, 10, 67, 42, 39]
Largest element: 67

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 4️⃣ Program to Copy All Elements from One Vector to Another

import java.util.Vector;

public class CopyVector {
    public static void main(String[] args) {
        Vector<String> colors1 = new Vector<String>();

        colors1.add("Red");
        colors1.add("Green");
        colors1.add("Blue");

        // Create a new Vector and copy all elements
        Vector<String> colors2 = new Vector<String>();
        colors2.addAll(colors1);

        System.out.println("Original Vector: " + colors1);
        System.out.println("Copied Vector: " + colors2);
    }
}

Output:

Original Vector: [Red, Green, Blue]
Copied Vector: [Red, Green, Blue]

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5️⃣ Implement a Vector of Strings and Search for a Given Word

import java.util.Scanner;
import java.util.Vector;

public class SearchWord {
    public static void main(String[] args) {
        Vector<String> words = new Vector<String>();
        Scanner sc = new Scanner(System.in);

        // Add words to the vector
        words.add("apple");
        words.add("banana");
        words.add("cherry");
        words.add("grape");
        words.add("mango");

        System.out.println("Words in Vector: " + words);

        // Input word to search
        System.out.print("Enter a word to search: ");
        String searchWord = sc.nextLine();

        // Check if word exists
        if (words.contains(searchWord)) {
            System.out.println(searchWord + " is found in the Vector!");
        } else {
            System.out.println(searchWord + " is NOT found in the Vector!");
        }

        sc.close();
    }
}

Example Output:

Words in Vector: [apple, banana, cherry, grape, mango]
Enter a word to search: grape
grape is found in the Vector!

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