Vectors in Java Collections

• Vector is like the dynamic array which can grow or shrink its size. 
• Vector is similar to ArrayList but threadsafe
• It is recommended to use the Vector class in the thread-safe implementation only else use ArrayList
• Iterator returned by Vector is fail-fast. Means any structural modification made to Vector like adding or removing elements during Iteration will throw java.util.ConcurrentModificationException.

It is similar to the ArrayList, but with two differences-

• Vector is synchronized.
• Java Vector contains many legacy methods that are not the part of a collections framework.

Example :

package java8;

import java.util.Vector;

public class VectorDemo {
	public static void main(String[] args) {
		 Vector<String> vec = new Vector<String>();  
         //Adding elements using add() method of List  
         vec.add("Tiger");  
         vec.add("Lion");  
         vec.add("Dog");  
         vec.add("Elephant");  
         //Adding elements using addElement() method of Vector  
         vec.addElement("Rat");  
         vec.addElement("Cat");  
         vec.addElement("Deer");  
           
         System.out.println("Elements are: "+vec);  
	}
}

Since it is similar to arraylist, the complexity of Vector is same

Complexity of Vector

Vector	Time Complexity	Space Complexity
Adding Element	O(1) – resize O(log(n))
Removing Element	O(n)
Iterating Elements	O(n)
Retreving Element at Position	O(1)

Reference :

https://www.interviewsansar.com/java-vector-time-complexity-and-how-vector-grows-in-java/