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Interview Questions and Answers - Order By Newest

Q1771. Which tools have you used in your previous projects ?

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Q1772. What are your short and long terms goals ?

General

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Q1773. Write a Program to convert a binary to number ?

Core Java

Ans. int convert(int binaryInt) {
int sumValue=0;
int multiple = 1;
while(binaryInt > 0) {
binaryDigit = binaryInt;
binaryInt = binaryInt /10;
sumValue = sumValue (binaryDigit * multiple);
multiple = multiple * 2;
}

return sumValue;
}

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Q1774. What are protocol buffers ?

Markup Language

Ans. Protocol buffers are language-neutral, platform-neutral, mechanism for serializing structured data. It is developed by google.

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Q1775. Can we discover end points of Rest API without looking at the code ?

Rest

Ans. Generally Rest services don't have any registry like we have WSDL is SOAP and hence don't have a way to know the end points without looking at either the url mapping in controller or client code. Some restful service publish WADL (Web Application Description Language) and hence clients can locate the service end points.

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Q1776. Can we deploy an application to server using a jar file ?

Java EE

Ans. Conventionally we need a WAR file to be deployed to server. Though with Spring Boot we can even deploy using jar.

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Q1777. What is the use of Annotations in Java ?

Core Java

Ans. Annotations are used to specify meta information about the code.

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Q1778. Are Annotations better than using XML configs ?

Core Java

Ans. Yes , as both code and its meta information reside in the same file, it promotes better readability and maintenability.

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Q1779. Why is goto not used in Java?

Core Java

Ans. Goto statement results in unstructured jumps in control from one code location to another and hence makes the code very difficult
to read , maintain and debug. Moreover Goto can always be replaced using other statements like break / continue and hence results in structured movement of programming control.

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Q1780. What is "convention over configuration" ? Which framework uses this design paradigm ?

Design

Ans. Convention over configuration is a way of software design used by frameworks that attempt to decrease the number of decisions that a developer is required to make without necessarily losing flexibility. The objective is to reduce the unnecessary configurations and follow conventions to accomplish that. For example - DB Entity and DB Table name conventionally should be same and hence shouldn't require configuring mapping between the two.

"Spring Boot" and "Ruby on Rails" have adopted this design principle.

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Q1781. Are there any disadvantages of "Convention over configuration" Design paradigm ?

Design

Ans. Yes, It may result in some loss of flexibility as the application has to follow all conventions. Moreover it can contradict with other design paradigms or principles used in the application or framework.

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Q1782. Can you give an example of "Convention over configuration" Design principle ?

Design

Ans. Hibernate mapping configurations are used for mapping hibernate entities and corresponding DB Tables. Conventionally Entities and Table can share the same name and hence framework can provide implicit mapping instead of explicit mapping through configurations. Though it may result in little loss of flexibility in extreme cases but will work with all applications following the convention.

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Q1783. Explain Interceptor Design Pattern ?

Design

Ans. It is used for intercepting the request. It's primary use is to implement security policy. All or specific request types can be intercepted and hence forwarded to authentication / authorization module so as to facilitate authorized requests to application.

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Q1784. What are the changes in Java 9 ?

Core Java

Ans. JVM and JDK are getting smaller.

New command line tool called jshell that will add native support and popularize a Java way to REPL (Read-Eval-Print-Loop)

private methods in interfaces

Introduction of the module system or project Jigsaw

JavaDoc Search

Light version of JSON API

HTTP2 client

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Q1785. What are the disadvantages of Adapter Design Pattern ?

Design

Ans. It introduces a layer of adaptations before it reaches the final and desired interface.

Moreover sometimes all requests are forwarded to adapter class. Some of such requests doesn't even require any sort of adaptions as they are qualified to call the final interface directly and introducing overheads.

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Q1786. What could be the real world example of Adapter Design Pattern ?

Design

Ans. Voltage converters / Power Adapters

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Q1787. What is project Jigsaw in Java 9 ?

Core Java

Ans. The projects aims to organize the Java source code into independent modules and hence facilitate building them independently.So now we will have multiple core java jars instead of single one. This way of organizing the code would offer following advantages

1. Will make applications lighter as only required modules will be built with the application. Moreover there are some legacy packages currently which anyone hardly use.

2. Reuse same class whole identifiers across different modules.

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Q1788. What does the modularity in project jigsaw means ?

Core Java

Ans. It means that now individual modules will be built independently instead of complete jdk built in a single jar file. So we will have multiple jars instead of single jar. Moreover this organization would result in lighter applications as they can just built themselves with the required jars and hence ignoring the not required and legacy modules.

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Q1789. What is meant Java is "Write Once Run Anywhere" ?

Core Java

Ans. It means that Java is compiled to byte code that is platform independent and hence can be run anywhere or any machine.

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Q1790. What is the difference between Enumeration and Iterator ?

Core Java

Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.

Enumeration is less safer than Iterator

Enumeration is fail safe whereas Iterator is fail fast

Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.

Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2

Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove

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Q1791. What is "dynamic method dispatch" in java ?

Core Java

Ans. dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java.

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Q1792. Can we override the overloaded methods too ?

Core Java

Ans. Yes. Both concepts are independent of each other. Overriding depends on the methods with same name and signature whereas Overloading on same name but with different signatures. All definitions of an overloaded method can be individually overridden in the derived class.

For example -

Class A has overloaded methods "public void myMethod(String str)" and "public void myMethod(int x)"

We can have derived class ClassB extends ClassA and hence can override both methods myMethod(String str) and myMethod(int x) in ClassB

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Q1793. What are the four situations that are required for deadlock to happen ?

Operating System

Ans. mutual exclusion i.e the resource is not shareable and hence a process should have exclusive access to it at a particular time

Hold and Wait i.e the process doesn't release all existing resources held by it before requesting for another one.

No preemption i.e noone can forcefully release a resource held by another process and the process should voluntarily release the resource held by it.

Circular Wait - For ex, P1 is waiting on resource to be released by P2, P2 is waiting on resource to be released by P3 and P3 is waiting on the resource to be released by P1

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Q1794. What is Livelock in relation to deadlock ?

Operating System

Ans. Livelock is when two threads or processes get deadlocked because they try to perform the same action to come out of a potential deadlock.

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Q1795. How can we get an array out of ArrayList ?

Core Java

Ans. We can get an array out of ArrayList by using toArray() method of an array list.

String a[] = arrayList.toArray();

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Q1796. What are the trade offs between public constructor and static final method ?

Core Java

Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.

With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.

Sample Code for constructor

Sample Code for factory

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Q1797. What will be the output of following code

Integer x = 1;
Integer y = 2;
System.out.println(x == y);

What if you change 1 to "1" and Integer to String?

Core Java

Ans. It will print "true" with integers as well as strings. The reason is "Integer constant pool" and "String pool"

String pool maintains pool of string literals. When a string literal is used for the first time, a new string object is created and is added to the pool. Upon it's subsequent usage , the reference for the same object is returned. Similarly java uses integer constant pool.

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Q1798. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?

Core Java

Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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Q1799. What is the difference between CountingSemaphore and a CountDownLatch?

Operating System

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Q1800. What is the trade off between using Collections.synchronizedList() on an ArrayList and a CopyOnWriteArrayList?

Core Java

Ans. Synchronized List locks the whole list to provide synchronization and thread safety during the read or write operation, while, CopyOnWriteArrayList doesn’t lock the whole list during these operations.
The CopyOnWriteArrayList class works according to its name i.e. copy-on-write which performs different actions for reading and write operations. For every write operation (add, set, remove, etc), it makes a new copy of the elements in the list. and for the read operations (get, iterator, listIterator, etc), it works on a different copy. So there is no additional overhead during a read operation and its read operation is faster than Collections.SynchronizedList(). Thus, COWAL is better for reading operation than Synchronized List.

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