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Category Archives: Core Java Interview Questions

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Sapient Global Markets Interview Questions – Set 3

Hey everyone, I am writing this article for the people who wants to appear for Sapient Global Markets. I appeared for Senior Application Developer I in Sapient Global Markets Bangalore on August 2017. I would Like to share my experience with you guys. I will cover Technical round question and some brief intro of Sapient GM process. […]

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 […]

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. […]

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

The difference between interface and abstract class 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 between them. With support of default methods (introduced in Java8) and private methods (introduced in Java9) in interface, the gap between […]

How does HashMap work internally in Java?

How does HashMap work internally in java is one of the most asked core java interview questions. Most of the candidates do not give the satisfactory explanation. This question shows that candidate has good knowledge of Collection. So this question should be in your TO-DO list before appearing for the interview. There are four things we should […]

How to create Immutable Class in Java

Immutable class is a class which once created, it's contents can not be changed. Immutable objects are the objects whose state can not be changed once constructed.  In Java, String  and all the wrapper classes e.g. Boolean, Integer, Long, etc are immutable classes. We can create our own immutable class as well. Joshua Bloch's Effective Java has a very good explanation about why you […]

Wrapper Classes | Interview Questions

April 22, 2017
Posted by Pumpkin

In this post, we will discuss some of the most asked interview questions on wrapper classes. Java is an object-oriented language and can view everything as an object. A simple file can be treated as an object (with java.io.File), an address of a system can be seen as an object (with java.util.URL) and an image can be treated as an […]

Singleton Design Pattern

In Design Pattern article we have seen different types of design pattern available. In this article we will take one of the simplest design pattern from the Creational Design Pattern. Singleton Design Pattern is part of the creational design pattern. In Singleton design pattern restricts the instantiation of a class and ensures that only one instance of the class […]


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