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Category Archives: Interview Questions


How is HashSet implemented internally in Java?

September 27, 2017
Posted by Pumpkin

In our previous article, we have seen internal implementation of SynchronizedMap and the difference between HashMap, Hashtable, SynchronizedMap and ConcurrentMap.  In this article, we will understand how does HashSet work internally? How JDK implementers have reused HashMap effectively for HashSet implementation.   The best way to understand internal implementation of any built-in Java class is by looking into its […]

Hashtable vs SynchronizedMap vs ConcurrentHashMap

Java Collection classes are heart of Java API.  It is essential to use built-in java collections like HashMap, ArrayList or LinkedList for accessing, storing and processing data in java applications. For Example, we have extensively used HashMap to transfer data between two layers of our MVC framework.   In all core java interviews, you will definitely face questions on […]

View vs Materialized View | Oracle SQL

September 10, 2017
Posted by Pumpkin

Every Java Developer is expected to have basic knowledge of database like SQL Queries, joins, having clause, group by, views, stored procedures, cursors, triggers, etc. If you are preparing for Java / J2EE interview, you should also prepare basic SQL interview questions. In our previous article on SQL interview Questions, we have seen differences between UNION and UNION […]

Program to find nth digit of the series 3, 5, 6, 9, 10, 12, …

August 20, 2017
Posted by Pumpkin

Bit Manipulation programming questions are integral part of any online coding challenges or programming rounds of 3-4 year exp Java/C/Python developer interviews. So, why are we talking about bit manipulation in this series problem? Lets look at the binary representation of all the numbers in this series. Decimal Digit Binary Representation 3 0011 5 0101 6 […]

Program to check if a given number is power of two or not?

August 20, 2017
Posted by Pumpkin

In this post, we will discuss about one of the easiest and commonly asked Bit Manipulation Interview Question i.e. Write a program to check if a given number is power of two or not?   This post is continuation of our previuos article Program To Find Number Of Set Bits In The Number.  Both of the approach […]

Program to find number of set bits in the Binary number

August 20, 2017
Posted by Pumpkin

In this post, we will discuss about one of the easiest and commonly asked Bit Manipulation Interview Question i.e. Find total number of set bits in the given number?  There are many approach to solve this problem. Here, we will discuss about below two approaches: & and >> Approach (Naive Approach) Brian Kernighan's Approach 1) & and >> Approach […]

Class Loader SubSystem | JVM Internals

August 5, 2017
Posted by Pumpkin

​In our previous article of JVM internals series, we learned about what is JVM, basic architecture of JVM and briefly understood its components. In this article we will discuss in detail about Class Loader SubSystem component of JVM architecture . Class Loader SubSystem Java’s dynamic class loading functionality is handled by the Class Loader SubSystem. […]

Program to find Unique Array Element

July 30, 2017
Posted by Pumpkin

Programming and coding interview questions are an integral part of any Java, Python or C++ application developer interview. No matter on which language you have expertise, good problem solving skills shows how efficient you are in solving any problem.  In this post, we will discuss one of the very commonly asked programming question. .!! Problem Statement: In […]

What is the use of private constructor in java?

In Java, we can use any access modifier (i.e. public, protected or private) with constructor.  So, what are the uses of making constructor private? First thing that strikes your mind is Singleton Design Pattern which is also one of the most asked Core Java Interview Question to the 3-4 yr exp Java developers.  Apart from creating singleton class, private constructor […]

Interface vs Abstract class in Java

July 7, 2017
Posted by Pumpkin

Interface has been evolved a lot in last two releases of java. Refer interface evolution in java for the same. However, there are still many differences between interface and abstract class. It is one of the most asked interview questions for entry level java developer interviews. Even though both are used to achieve abstraction in java, there are significant differences […]

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