Difference between Vector and Arraylist is the most common  Core Java Interview question you will come across in Collection .  This question is mostly used as a start up question by the Interviewers before testing deep  roots of  the Collection  .
Vector , ArrayList classes are implemented using dynamically resizable  array providing fast random access and fast list traversal very much like using an ordinary array . ArrayList  support dynamic arrays that can grow as needed that is ArrayList can be dynamically increased or decreased in size .

Read Also :    Difference between  HashMap and ConcurrentHashMap

Arraylist vs Vector in Java

1.  Synchronization and Thread-Safe

Vector is  synchronized while ArrayList is not synchronized  . Synchronization and thread safe means at a time only one thread can access the code .In Vector class all the methods are synchronized .Thats why the Vector object is already synchronized when it is created .

2.  Performance

Vector is slow as it is thread safe . In comparison ArrayList is fast as it is non synchronized . Thus     in ArrayList two or more threads  can access the code at the same time  , while Vector is limited to one thread at a time.

3. Automatic Increase in Capacity

A Vector defaults to doubling size of its array . While when you insert an element into the ArrayList ,      it increases
its Array size by 50%  .

By default ArrayList size is 10 . It checks whether it reaches the       last  element then it will create the new array ,copy the new data of last array to new array ,then old array     is garbage collected by the Java Virtual Machine (JVM) .

4. Set Increment Size

ArrayList does not define the increment size . Vector defines the increment size .

You can find the following method in Vector Class

public synchronized void setSize(int i) { //some code  }

There is no setSize() method or any other method in ArrayList which can manually set the increment size.

5. Enumerator

Other than Hashtable ,Vector is the only other class which uses both Enumeration and Iterator .While ArrayList can only use Iterator for traversing an ArrayList .

6.  Introduction in Java 

java.util.Vector  class was there in java since the very first version of the java development kit (jdk).
java.util.ArrayList  was introduced in java version 1.2 , as part of Java Collections framework . In java version 1.2 , Vector class has been refactored to implement the List Inteface .

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