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

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Q211. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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Q212. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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Q213. Difference between jar , war and ear ?

Java EE

Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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Q214. Do you know the way to remove unused imports automatically in eclipse ?

Eclipse

Ans. Select the package -> Right Click -> Source -> Organize Imports.

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.

Q215. Differences between abstract class and interface ?

Core Java

Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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Q216. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));

Core Java

Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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Q217. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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Q218. If we add Enum constants to a sorted collection ( Treemap , TreeSet ), What will be the order in which they will be maintained ?

a. Sorted Collection wont maintain them in any order.
b. Insertion Order
c. Order in which constants are declared.
d. Natural Sorting Order.

Ans. Order in which constants are declared.

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Q219. What is RI or Reference Implementation ?

Ans. RI or Reference Implementation is a sample implementation provided for the API's / Specs, usually by their developers. This is usually a part of API documentation.

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Q220. How is multiple inheritance implemented in Java ?

Core Java

Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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Q221. What is a Destructor ? Do we have Destructors in Java ?

Core Java

Ans. Destructor is used to de-allocate memory allocated by objects.

There are no destructors in Java. Alternatively, Java provides Automatic garbage collection i.e automatically releasing the un-referenced memory.

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Q222. What is use of Revert in SVN?

Tools

Ans. Revert your local changes.

There are 2 types of reverts -

1) Local Revert: It will delete all changes from files which you made after updates and before commit.
2) Repo Revert: Upload the changes to previous Repo.

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Q223. What is a compilation unit in Java ?

Ans. Java Source Code File

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Q224. What is a package and what are its advantages ?

Core Java

Ans. Package is a namespace that organizes a set of related classes.

Advantages of Packages

1. Better Organization of classes.
2. Saves from the problem of duplicate names as duplicate class names are allowed across different packages.

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Q225. Which method needs to be implemented if a class is implementing comparable interface ?

Core Java

a. comp

b. compare

c. compareTo

d. compareEquals

Ans.c. compareTo

Q226. What is the relationship between Vehicle and Engine in this example ?

public class Vehicle {
   Enginer engine;
   public void move(){
      engine = new Engine();
      engine.start();
   }
}

Core Java

a. Composition ( Vehicle has a Engine )

b. Composition ( Engine has a Vehicle )

c. Inheritance ( Vehicle is a Engine )

d. Inheritance ( Engine is a Vehicle )

Ans.a. Composition ( Vehicle has a Engine )

Q227. What is the relationship between Car and Vehicle in the following code ?

public class Car extends Vehicle{
   Engine engine;

   public static void main(String[] args){
      Vehicle vehicle = new Car();
      car.move();
   }

   public void move(){
      engine = new Engine();
      engine.start();
   }
}

Core Java

a. Composition ( Vehicle has a Car )

b. Composition ( Car has a Vehicle )

c. Inheritance ( Vehicle is a Car )

d. Inheritance ( Car is a Vehicle )

Ans.d. Inheritance ( Car is a Vehicle )

Q228. What is the problem with the following code ?

public class Car extends Vehicle{
   Vehicle vehicle;

   Car(){
      super();
      this.vehicle = new Vehicle();
   }
}

Core Java

a. There is an Inheritance as well as Composition relationship between Vehicle and Car which is not permitted

b. We cannot initialize the parent class instance within the constructor

c. Call to super is illegal

d. There is no problem

Ans.d. There is no problem

Q229. Which of the following wildcard is used to import multiple packages at once ?

Core Java

a. .

b. ?

c. *

d. &