Core Java - Interview Questions and Answers for 'Basic' | Search Interview Question

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Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS)

Q211. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

Core Java

Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

Sample Code for String

Sample Code for StringBuffer

Sample Code for StringBuilder

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Frequently asked to fresh graduates.

Q212. Is JVM, a compiler or interpretor ?

Ans. Its an interpretor.

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Recently asked in Infoview Technologies.

Q213. What is a Default Constructor ?

Core Java

Ans. The no argument constructor provided by Java Compiler if no constructor is specified.

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Q214. Can we overload constructors ?

Ans. Yes.

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Q215. What will happen if we make the constructor private ?

Core Java

Ans. We can't create the objects directly by invoking new operator.

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Q216. Is it necessary that each try block to be followed by catch block ?

Core Java

Ans. It should be followed by either catch or finally block.

Sample Code for Retry in case of exception

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Q217. Difference between nested and inner classes ?

Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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Q218. What is reflection ?

Ans. It is the process of examining / modifying the behaviour of an object at runtime.

Sample Code for reflection

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Q219. What is suspend() method used for ?

Ans. suspend() method is used to suspend the execution of a thread for a period of time. We can then restart the thread by using resume() method.

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Usually asked only to fresh graduates.

Q220. Difference between suspend() and stop() ?

Ans. Suspend method is used to suspend thread which can be restarted by using resume() method. stop() is used to stop the thread, it cannot be restarted again.

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Q221. What are the benefits of using Spring Framework ?

Spring

Ans. Spring enables developers to develop enterprise-class applications using POJOs. The benefit of using only POJOs is that you do not need an EJB container product.

Spring is organized in a modular fashion. Even though the number of packages and classes are substantial, you have to worry only about ones you need and ignore the rest.

Spring does not reinvent the wheel instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies.

Testing an application written with Spring is simple because environment-dependent code is moved into this framework. Furthermore, by using JavaBean-style POJOs, it becomes easier to use dependency injection for injecting test data.

Spring is web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks.

Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.

Lightweight IoC containers tend to be lightweight, especially when compared to EJB containers, for example. This is beneficial for developing and deploying applications on computers with limited memory and CPU resources.

Spring provides a consistent transaction management interface that can scale down to a local transaction

Sample Code for spring

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Q222. what is the difference between collections class vs collections interface ?

Core Java

Ans. Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection.

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Q223. What is Scanner class used for ? when was it introduced in Java ?

Core Java

Ans. Scanner class introduced in Java 1.5 for reading Data Stream from the imput device. Previously we used to write code to read a input using DataInputStream. After reading the stream , we can convert into respective data type using in.next() as String ,in.nextInt() as integer, in.nextDouble() as Double etc

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Q224. Whats the purpose of marker interfaces ?

Ans. They just tell the compiler that the objects of the classes implementing the interfaces with no defined methods need to be treated differently.

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. Frequently asked in HCL Technologies, TCS and Accenture.

Q225. What is the difference between final, finally and finalize() ?

Core Java

Ans. final - constant variable, objects cannot be de-referenced, restricting method overriding, restricting class sub classing.

finally - handles exception. The finally block is optional and provides a mechanism to clean up regardless of what happens within the try block. Use the finally block to close files or to release other system resources like database connections, statements etc.

finalize() - method helps in garbage collection. A method that is invoked before an object is discarded by the garbage collector, allowing it to clean up its state.

Sample Code for final

Sample Code for finally

Sample Code for finalize

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Frequently asked to fresh graduates.

Q226. Explain Thread States ?

Operating System

Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities.

Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn.

Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish.

Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method.

Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes.

Blocked on synchronization - Will move to Runnable when a lock is acquired.

Dead - The thread is finished working.

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Q227. What is XML ?

Xml

Ans. XML or eXtensible Markup Language is a markup languages for describing data and its metadata.

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Q228. Which load testing tools have you used ?

Ans. Rational Robot, JMeter, LoadRunner

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Frequently asked in CTS ( Based on 2 feedback )

Q229. What is the difference between comparable and comparator in java.util pkg?

Core Java

Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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Recently asked in TCS , Tech Mahindra, HCL , Accenture and Fidelity.

Q230. Explain Flow of Spring MVC ?

Spring

Ans. The DispatcherServlet configured in web.xml file receives the request.

The DispatcherServlet finds the appropriate Controller with the help of HandlerMapping and then invokes associated Controller.

Then the Controller executes the logic business logic and then returns ModeAndView object to the DispatcherServlet.

The DispatcherServlet determines the view from the ModelAndView object.

Then the DispatcherServlet passes the model object to the View.

The View is rendered and the Dispatcher Servlet sends the output to the Servlet container.

Finally Servlet Container sends the result back to the user.

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Very frequently asked.Usually among first few questions.

Q231. What is MVC ?

Design

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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Q232. Explain Inner Classes ?

Core Java

Ans. The accessibility (public, protected, etc.) of the inner class is defined by the outer class.

Just like top-level classes, an inner class can extend a class or can implement interfaces.

Similarly, an inner class can be extended by other classes, and an inner interface can be implemented or extended by other classes or interfaces.

An inner class can be declared final or abstract.Inner classes can have inner classes, but you will have a hard time reading or understanding such complex nesting of classes.

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Q233. What is the advantage of using arrays over variables ?

Ans. Arrays provide a structure wherein multiple values can be accessed using single reference and index. This helps in iterating over the values using loops.

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Q234. When you will synchronize a piece of your code?

Ans. When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.

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Q235. What is connection pooling?

Database

Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.

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Q236. Advantage of Collection classes over Arrays ?

Core Java

Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment.
Collections can hold both homogeneous and heterogeneous data's.
Every collection follows some standard data structures.
Collection provides many useful built in methods for traversing,sorting and search.

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Q237. What is the difference between float and double?

Ans. Float can represent up to 7 digits accurately after decimal point, where as double can represent up to 15 digits accurately after decimal point.

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Q238. What is the difference between System.out ,System.err and System.in?

Ans. System.out and System.err both represent the monitor by default and hence can be used to send data or results to the monitor. But System.out is used to display normal messages and results whereas System.err is used to display error messages and System.in represents InputStream object, which by default represents standard input device, i.e., keyboard.

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Q239. Why is Java considered Portable Language ?

Core Java

Ans. Java is a portable-language because without any modification we can use Java byte-code in any platform(which supports Java). So this byte-code is portable and we can use in any other major platforms.

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Q240. Difference between throw and throws ?

Core Java

Ans. throw is used to explicitly throw an exception especially custom exceptions, whereas throws is used to declare that the method can throw an exception.

We cannot throw multiple exceptions using throw statement but we can declare that a method can throw multiple exceptions using throws and comma separator.

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