Interview Questions and Answers for 'C' | Search Interview Question

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Q451. Why can't we create an instance of abstract class ? Why is it restricted by compiler ?

Core Java

Ans. Because Abstract class is incomplete i.e there are abstract methods that needs to be defined by extending classes.

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Q452. Why do we need polymorphism in Java ?

Core Java

Ans. Frankly saying I dont see much use of method overloading as its just little design convenience as you can use the same name but still have binding to different methods depending on the need.

Method overriding is really important and is much more useful than method overloading. Along with other programming concepts like interfaces and dependency injection , it facilitates the development of software as libraries and plug-gable components.

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Q453. What is the difference between a keyword and a modifier ?

Core Java

Ans. Keywords are the reserved words that have a pre defined meaning for a compiler whereas modifiers are the type of keywords that modifies the state or definition of a programming construct.

for, while are keywords but not modifiers.
private , public , final , abstract etc are keywords as well as modifiers.

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Q454. In which cases using SOAP is preferred over REST ?

Web Service

Ans. SOAP services are better in case we need to establish a formal and detail contract with the client or callers and hence suitable for

1. Services published for much wider unknown audience
2. Require large input payload
3. Requiring different level for authentication

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Q455. What is the difference between keywords, identifiers and literals in java ?

Core Java

Ans. Keywords are the reserved words that have a pre defined meaning for the compiler and hence are restricted to be used as identifiers.

Identifiers are the name assigned to different programming constructs like classes, interfaces, methods , variables etc.

Literals are the values that are assigned to Identifiers.

For example

int count = 0;

in the above statement "int" is a keyword, "count" is an identifier and "0" is a literal

Sample Code for keywords

Sample Code for identifiers

Sample Code for literals

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Q456. How does java identifies which method to be called in method overriding or runtime polymorphism, when both methods share the same name and signature ?

Core Java

Ans. Java identifies the method to be called at runtime by the object that is being referenced.

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Q457. What are some uses of interceptors ?

Java EE

Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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Q458. What is Eclipse vert.x ?

Ans. Eclipse Vert.x is a tool kit for building reactive applications on the JVM. Vert.x is event driven and non blocking. This means the application can handle lot of concurrency using a small number of kernel threads. Vert.x lets the application scale with minimal hardware.

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Q459. What is the difference between following two segments of code

Code 1

int x = 4 * 3;
int y = x * 5;

Code 2

int y = 4 * 3 * 5;

Core Java

Ans. Both will produce the same output but 1st will consume more resources in terms of memory ( for maintaining intermediate value ) and computing power ( as single mathematical calculation with more operands is more effective than multiple calculations with broken down operands )

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Q460. Java doesn't provide exclusive access to memory like C/C++ and other lower level languages ? What are the advantanges and disadvantages ?

Core Java

Ans. Yes, doesn't provide exclusive access as we cannot allocate and deallocate memory exclusively as Java internally manages it. The advantage of this is that it relieves the coder for such tasks and helps protect from many bugs that may get introduced with imperfect coding. Moreover as java garbage collector collects all unclaimed memory or objects, it helps the application from memory leaks.

On the flip side , as coder doesn't have extensive excess to memory , it is upto java to decide on the state for programming construct and data storage and hence may introduce some security risks. For example - Java keeps string literals in string pool and there is no exclusive way to remove it and hence may stay and sensitive data in string pool may introduce security issues. Moreover when we overwrite a value or object for a variable / reference, it is upto java to purge those values and hence it may stay in memory for a while till java decide that it is no longer referenced and hence should be removed and hence makes it vulnerable for inappropriate access.

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Q461. Is it ok to use optional everywhere just to get over nullpointerexception ?

Core Java

Ans. Optional is to be used for arguments / atrributes which are indeed optional i.e the request should continue even if they aren't provided. It should not be used for mandatory attributes or arguments as we would like application to shout out ( with error message / exception trace ) to signify a problem.

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Q462. Do you prefer using var args ?

Core Java

Ans. Though var args are used rarely but they are pretty useful if a method is expected to receive variable number of arguments. For example - it's pretty useful for the main method as the caller has the flexibility to provide arguments in infinite ways.It provides a convenience and flexibility to the caller.

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Q463. What are the types of applications we can create using Elastic Beanstalk ?

Amazon Web Services (AWS)

Ans. Web Server and Worker

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Q464. What is meant by "Vector is synchronized and ArrayList isn't " ?

Core Java

Ans. It means that only 1 thread can access have access to Vector at a time and no parallel access is allowed whereas Array List allows parallel access by multiple threads.

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Q465. Can a class be declared "protected" ?

Core Java

Ans. No, only methods can be declared protected.

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Q466. Is String final in Java ?

Core Java

Ans. Strings are immutable in Java and not final.

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Q467. Write a program for LinkedList, with method to append node and traversing the list ?

Algorithm

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }

   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();

   }
}

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Q468. Write method to delete Node from a LinkedList.

Data Structure

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }

   private void deleteNode(Integer value) {
      head = start;
      while (head.nextNode != null) {
         if(head.nextNode.body == value){
            head.nextNode = head.nextNode.nextNode;
         }

         head = head.nextNode;
      }
   }



   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();

      ll.deleteNode(10);

      ll.traverse();

   }
}

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Q469. What are ascii values for capital and lower case alphabets ?

Core Java

Ans. 65 to 90 for capital case alphabets

97 to 122 for lower case alphabets

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Q470. What is the difference between pop and peek function of stack ?

Data Structure

Ans. pop method pulls the top element from the stack and then move the top to the next element whereas peek only get the top element but doesn't move the top.

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Q471. How can we ensure thread safety in static method ?

Core Java

Ans. By using synchronized static method or synchronized block

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Q472. Write a method it will return reverse of the string(with out using reverse method of String or StringBuffer)

Core Java

Ans. String s1 = "akhilesh";
char[] ch = s1.toCharArray();
for (int i = ch.length-1 ; i >=0 ; i--) {
System.out.print(ch[i]);
}

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Q473. What is abstraction ?

Design

Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user.

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Q474. Which collection stores element in insertion order ?

Core Java

Ans. LinkedList maintains the insertion order in collection.

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Q475. What are the reasons to choose between reserved and on demand instances ?

Server

Ans. In terms of compute options and configurations, Reserved Instances and On Demand instances are the same. The only difference between the two is that a Reserved Instance is one you rent (reserved) for a fixed duration, and in return you receive a discount on the base price of an On Demand instance.

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Q476. Find different combination of given String and trace the output

Core Java

Ans. private void permutation(String prefix, String sufix)
{
int ln = sufix.length();
if(ln == 0) {
System.out.println(prefix);
} else {
IntStream.range(0, ln).forEach(i->permutation(prefix sufix.charAt(i), sufix.substring(0,i) sufix.substring(i 1, ln)));
}
}

call:permutation("", "abcdef");

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Q477. Can you explain the integration between API Gateway and Lambda if we wish to develop services using these tools.

Amazon Web Services (AWS)

Ans. We can create API gateway and give the name of lambda function in order to be linked with lambda function, deploy the API and whenever request will be made from API it will directly be linked to lambda function to perform further process.

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Q478. Why do we need to specify import statement ? Don't you think Java could have been designed in such a way to automatically import everything that's in the class path ?

Core Java

Ans. Java could design it in such a manner but would result in ambiguity if there are multiple files with the same name. The only way to get over it to show the message when you use any such class to provide explicit import with the package prefix. The other problem could be that Java might have to change the early import to Late import and check what's being used to decide what needs to be imported as otherwise you will see errors regarding the ambiguous imports with duplicate file name.

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Q479. Which of the OOP's feature is most important ?

Core Java

Ans. Encapsulation facilitate hiding and restricted access and hence more of a security feature. Encapsulation is definitely a great feature as when applications expand criss cross communication between objects / modules could lead to blunders.

Inheritance facilitates code reuse.

Polymorphism comprise of method overloaded ( which to me is negligible usage ) and method overriding. Method overriding is of great usage as it facilitates concept of interfaces and plugin development.

So it’s Security / Organization vs

Code Reuse / Support for other features like overriding vs

Contracts / Plugin Development facilitating the creation of frameworks / libraries.

Which is more important may vary from application to application , its scale , its use , its sensitivity etc.

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Q480. Can we have a private default method ?

Core Java

Ans. No. The whole idea of default method is to provide a default definition in case the implementing class intend to provide definition for only some of the methods. Making any of the interface method private would restrict it from being implemented by the implementing class. So default method is an option to provide implementation and not restricting a new definition.

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