Java Interview Questions and Answers

What is the Vector class?
The Vector class provides the capability to implement a growable array of objects.
What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection .
Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.
What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars
What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region .
What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar .
What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
What is the highest-level event class of the event-delegation model?
The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
What is the Collection interface?
The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements. .
What is the difference between the size and capacity of a Vector?
The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.
Can a vector contain heterogenous objects?
Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
Can a ArrayList contain heterogenous objects?
Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.
What is an enumeration?
An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection. Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList? The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.
Can a vector contain heterogenous objects?
Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
Describe synchronization in respect to multi-threading?

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors. 

Latest Updates


A person is to count 4500 currency notes. Let an denote the number of notes he counts in the nth minute. If a1 = a2 = .... = a10 = 150 and a10 , a11 ,... are in an AP with common difference – 2, then the time taken by him to count all notes is ?

The value of product 6 1/2 * 6 1/4 * 6 1/8 * 6 1/16 * -----∞ upto infinite terms?


What is nohup command in unix?

How do display the 10th, 11th and 12th line of a file in Unix?


The mean of 100 students marks was found to be 40. it was found later that a mark 53 was read as 83. the correct mean is?


The geometric mean of three observations 40, 50 and X is 10, then the value of X is ?

Indian Politics

Who appoints the members of National human rights commission?

The President of India can resign by writing under his hand addressed to?

Under which article of the constitution of India can the President of India refer a matter to the Supreme Court for its opinion?

General Computer Knowledge

The term VPN stands for ?

The transmission control protocol(TCP) is a............ layer protocol ?

Oracle PL/SQL

What is the difference between Procedure and Function?

Define exception and How will you raise an exception in PL/SQL procedure?

What is the advantage of using packages for storing PL/SQL objects?

Fill in the blank

I ________ station before the train arrived.

If I ______ a king, I would help everyone.

Radha___________her daughter for an hour.

Errors Identification

Find out which part of the sentence below has an error and mark the option accourdingly -
Sohan was married in 1990 and have three children.