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

Interview Questions and Answers - Order By Newest

Q1161. Is JDK required on each machine where a Java application needs to be run ?

Core Java

Ans. No, to run application, machine needs just a JRE (Java Runtime Environment)

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Q1162. What is the purpose of re throwing the exception when we can provide the handling at the first catch itself ?

Core Java

Ans. Sometimes the calls move across layers of classes and functions and hence each layer needs to perform some function like cleaning if something goes wrong deep inside.

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Q1163. What is the problem we could face if we be very liberal with importing classes even if we are not using them ? For example

import java.util.*;
import java.io.*;

Core Java

Ans. It makes application little heavy as we are importing classes that aren't required.

It creates class name conflicts as similar name classes might be available across different packages. In case of such conflicts, we will have to specify the package name with the class name at the time of it's usage.

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Q1164. Which java package is loaded by default and hence doesn't require an explicit import statement ?

Core Java

Ans. java.lang

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Q1165. How do we define constant variables in Java ?

Core Java

Ans. By using static and final modifiers.

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Q1166. Can a source file contain more than one class declaration ?

Core Java

Ans. Yes, but only one of them can be declared public.

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Q1167. Can an interface be defined inside a class just like we can have inner classes inside a class ?

Core Java

Ans. Yes , we can have an interface that is part of a class.

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Q1168. Can an interface implements another interface ?

Core Java

Ans. No. No interface provides any implementation and hence the declaration isn't viable.

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Q1169. Why doesn't java support operator overloading ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

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Q1170. What is the use of upcasting in Java ?

Core Java

Ans. Interfacing

Car extends Vehicle

Car car = new Car();

// now you need to call an API changeTires() which can change tires for all Vehicle Types and accepts argument of type Vehicle and hence you will have to upcast it

changeTires((Vehicle)car);

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Q1171. Why do we pass an array of strings to main method ?

Core Java

Ans. Array of strings in the main method are the list of arguments or parameters which are sent to the application / program.

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Q1172. In Java, what is the closest thing to pointers?

Core Java

Ans. References.

Unlike pointers in C , Java references are strongly typed and we cannot do pointer arithmetics with them.

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Q1173. In Java, would you like to see an explicit destructor?

Core Java

Ans. Yes , a gc method to explicitly call garbage collection immediately on the object. It will provide better flexibility over application that require optimal usage of memory.

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Q1174. How to calculate lcm of two numbers ?

Core Java

^{This question was recently asked at 'HCL Tech'.This question is still unanswered. Can you please provide an answer.}

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Q1175. Write a Program to find age by birth date ?

Core Java

Ans. LocalDate today = LocalDate.now();
LocalDate birthday = LocalDate.of(1960, Month.JANUARY, 1);
Period p = Period.between(birthday, today); //Now access the values as below
System.out.println(period.getDays());
System.out.println(period.getMonths());
System.out.println(period.getYears());

Sample Code for LocalDate

Sample Code for Period

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Q1176. What is a session bean ?

Java EE

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Q1177. Explain Inheritance and Polymorphism.

Core Java

Ans. Getting parent class object properties into child class is called Inheritance.

The process of representing one form into multiple forms is called polymorphism.

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Q1178. What will be the output of following code

class TestMain {
public static void main(String[] args) {
String s1 = "ravi";
String s2 = new String("ravi");
Integer i = 10;
Integer a1 = new Integer("10");
System.out.println(s1 == s1);
System.out.println(i == a1);
}
}

Core Java

Ans. false
false

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Q1179. Will the following code compile ?

final HashMap hm = new HashMap();
hm.put("Ravi", 221);

Core Java

Ans. Yes, it will compile without error. final in this context means that the reference hm cannot be assigned to a new hash map but didn't restrict from changing the state of collection already held by hm.

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Q1180. Explain Java 8 concurrency mechanism.

Core Java

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Q1181. What is the difference between being final and being immutable ? Are string final or immutable in Java ?

Core Java

Ans. Being final in the sense of objects or object reference means that the reference cannot be reassigned to a different object whereas being immutable means that the object contents cannot be changed.

Strings in Java are immutable.

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Q1182. What does the following initialization mean ?

ArrayList<LinkedList> traversalPaths = new ArrayList<LinkedList>();

What could be the use of such a collection.

Core Java

Ans. Initialize an ArrayList that will hold LinkedLists i.e every element of the arraylist will be a linked list.

Such collection could be used in algorithms that require first random access and then sequential traversal. For example - Storing traversal paths for a graph wherein we can start from any vertex. Implementing dictionary with each arraylist element holding staring with character and then linked list holding duplicate words.

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Q1183. What will be the output upon executing main method

public class Graph {
   private static Multimap<Integer,Integer> adjacentDirectedNodesMap = ArrayListMultimap.create();

   Graph(){
      adjacentDirectedNodesMap.put(1, 2);
      adjacentDirectedNodesMap.put(1, 3);
      adjacentDirectedNodesMap.put(1, 4);
      adjacentDirectedNodesMap.put(3, 5);
      adjacentDirectedNodesMap.put(4, 5);
   }

   public static void main(String[] args){
      ArrayList visited = new ArrayList();

      Integer startNode = 1;

      for(Integer adjacentNodes: adjacentDirectedNodesMap.get(startNode)){
            System.out.println(adjacentNodes);
      }
   }
}

Core Java

Ans. Nothing as we haven't yet created an instance and hence adjacentDirectedNodesMap won't be initialized with any value and hence is empty.

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Q1184. What is the difference between return and continue statement ?

Core Java

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

continue statement is used within a loop to start next iteration without executing the remaining statements in the loop.

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Q1185. What is the difference between return and break statement ?

Core Java

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

break statement is used within a loop to move control out of the loop.

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Q1186. What is the difference between Java SE Map and Apache Commons MultiMap ? How can we implement functionality similar to multimap using Java SE map ?

Core Java

Ans. We can have duplicate keys within MultiMap whereas we cannot have duplicate keys within Java Util Map.

We can have a Map with value as a "collection of values" instead of single value to have a similar function as Multimap.

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Q1187. What is the difference between hasNextInt and nextInt method of scanner class ?

Core Java

Ans. The hasNextInt() is used to check if there are any more elements left and the nextInt() is used to access that element.

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Q1188. Is it a bad practice to initialize object reference to Null ?

Core Java

Ans. never initialise local to null,yes it is bad pratice

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Q1189. What will be the output of following code and Why ?

int x = 5;
int y = 7;
float f = 5f;
float z = y / x * f;
System.out.println(z);

Core Java

Ans. 5.0

operation between two ints generate int only. so 7/5 generates 1 and not 1.4. Multiplication between int and float generates float and hence

1 * 5.0 = 5.0

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Q1190. How do you know if a method is a constructor ?

Core Java

Ans. Is the method name same as class Name - Yes

Does the method have any return type ( even void ) - No

It's a constructor

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