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. 

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General Computer Knowledge

What kind of material does ‘IC’ in computers made of?


The force required to produce an acceleration of 4 m/s2 in an object of mass 9 kg is?


Some seeds have hooks and spines. It helps the seeds to__________?


Which of the following modes of heat transfer is faster?


Which of the following reproduces from underground stem?


Lichens are a symbiotic association of?


The unit of relative density is?

Problems on Ages

The ages of Gyanendra and Jitendra are in the ratio of 12:7 respectively. After 6 years, the ratio of their ages will be 3:2 respectively . find the difference in their ages?

Time and Work

X can do a piece of work in 20 days, while Y can do in 10 days. If Y worked at it for 8 days,then X can finish the remaining work in______.?


In a certain code, BELIEF is written as AFKKDI. How is SELDOM written in that code?

Ratio and Proportion

Find the mean proportional between 8 and 32 ?


A certain company has 120 employees who are engineers. Here, engineers constitute 30% of its work force. How many people are employed in the company?


From a well-shuffled deck of 52 cards, one card is drawn at random. Find the probability of getting a face card?

Profit and Loss

What percent profit is made by selling an article at a certain price if by selling at 2/3rd of that price, there would be a loss of 30%?


Among five people with monthly income of Rs. 14000, Rs. 25000, Rs. 15000, Rs. 18000 and Rs.49000, how many will have income less than the mean income of the five people?

Problems on Trains

A train 100 meters long moving at a speed of 40 km/hr crosses a train 130 meters long coming from the opposite direction in 6 seconds. Find the speed of the second train?

Permutation and Combination

In how many different ways can the letters of the word ‘DESIGN’ be arranged so that the vowels are at the two ends?


If sinA= 8/17 and cosA=15/17, then cotA=?