Vector

The Vector Class in Java

The Vector class is one of the oldest implementations of the List interface in the Java Collection Framework. It was introduced in Java 1.0 and represents a dynamic array similar to ArrayList. However, unlike ArrayList, Vector is synchronized, making it thread-safe.

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Key Characteristics of Vector

• Synchronized (thread-safe)
• Dynamic resizing
• Legacy collection
• Slower than ArrayList due to synchronization

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Common Use Cases

• Legacy systems
• Situations requiring built‑in synchronization
• When explicit thread safety is needed without wrappers

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Important Methods

Method	Description
addElement(E obj)	Adds element to vector
elementAt(int index)	Returns element at index
insertElementAt(E obj, int index)	Inserts element at index
removeElementAt(int index)	Removes element at index
removeAllElements()	Clears vector
capacity()	Returns internal capacity
setSize(int newSize)	Changes size

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Example 1: Basic Vector Operations

import java.util.Vector;

public class VectorExample {

    public static void main(String[] args) {

        Vector<String> fruits = new Vector<>();

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

        System.out.println(fruits);

        System.out.println("First fruit: " + fruits.elementAt(0));

        fruits.set(1,"Mango");

        System.out.println("After replace: " + fruits);

        fruits.remove("Cherry");

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

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Example 2: Capacity Growth

import java.util.Vector;

public class VectorCapacityExample {

    public static void main(String[] args) {

        Vector<Integer> numbers = new Vector<>(2);

        numbers.add(10);
        numbers.add(20);
        numbers.add(30);

        System.out.println(numbers);

        System.out.println("Capacity: " + numbers.capacity());
    }
}

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Example 3: Thread‑Safe Iteration

import java.util.Vector;

public class VectorThreadSafetyExample {

    public static void main(String[] args) {

        Vector<String> tasks = new Vector<>();

        tasks.add("Task 1");
        tasks.add("Task 2");

        synchronized(tasks) {
            for(String task : tasks) {
                System.out.println(task);
            }
        }
    }
}

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Performance Characteristics

Operation	Complexity
get()	O(1)
set()	O(1)
add()	O(1) amortized
remove()	O(n)

Synchronization overhead makes operations slower than ArrayList.

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When to Use Vector

Use Vector when:

• Legacy APIs require it
• Built‑in synchronization is necessary

Prefer alternatives:

• ArrayList
• Collections.synchronizedList()
• CopyOnWriteArrayList

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Vector vs ArrayList

Feature	Vector	ArrayList
Thread Safety	Synchronized	Not synchronized
Performance	Slower	Faster
Resizing	Doubles capacity	Grows by ~50%
Introduced	Java 1.0	Java 1.2