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Interview Questions and Answers - Order By Rating

Q3391. Find the repeating number using O(n) time and constant space.

Algorithm

Ans. http://www.geeksforgeeks.org/find-duplicates-in-on-time-and-constant-extra-space/

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Q3392. Write a method to convert all elements of a set to lower case.

Core Java

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+convert+all+elements+of+a+collection&category=code

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Q3393. Write java code to Get all words from a String and display them

Core Java

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=+Get+all+words+from+a+String&category=code

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Recently asked in Sophos

Q3394. Write a Method to get a map of words and their count by passing in the string

Core Java

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+get+a+map+of+words&category=code

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Q3395. Write code for singleton class

Design

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=singleton+class&category=code

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Q3396. Have you ever looked into internal implementation of Java Collections ?

Ans. Yeah, I once looked into implementation of TreeSet and TreeMap just for learning.

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Q3397. What will happen if we don't have termination statement in recursion ?

Ans. Function call allocates a stackframe in stack. Every stackframe will use some memory to store local variables, parameters and to remember return address. Without terminating condition stackframes will keep consuming memory from stack and eventually program will result in stackoverflow error.

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Q3398. How is static and dynamic polymorphism achieved in Java ?

Core Java

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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Q3399. Why can't we declare a class abstract as well as final ?

Core Java

Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.

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Q3400. What are different types of classes ?

Core Java

Ans. There are different verticals in which Java Classes can be classified.

1. Access - Public , Private , default or Protected.

2. Packaging - System, library or User Defined

3. Structure - Outer or Inner

4. Object Derivation - Abstract Class or Concrete Class.

5. Object Creation - Normal, Singleton , Doubleton , Immutable or Enum.

6. Functionality - String , Util , Stream etc.

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Q3401. Write a program / method to input few numbers and then print the sum.

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=946

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Very frequently asked to fresh graduates. Frequently asked in NSEiT and Accenture India

Q3402. Write a program to Generate prime numbers till a given number

Core Java

Ans. public class Main {
public static void main(String args[]) {
int number = 2;
int count = 0;
long sum = 0;
int givenNumber = 1000;
while (count < givenNumber) {
if (isPrimeNumber(number)) {
sum = number;
count;
}
number;
}
System.out.println(sum);
}
private static boolean isPrimeNumber(int number) {
for (int i = 2; i <= number / 2; i) {
if (number % i == 0) {
return false;
}
}
return true;
}
}

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Q3403. Write a program to calculate factorial of a number using recursion

Core Java

Ans.

public class Factorial {
   public static void main(String[] args){
      int x = 5;

      System.out.println(calculateFactorial(x));

   }

   private static int calculateFactorial(int x){
      if(x==1){
         return 1;
      }
      return x * calculateFactorial(x-1);
   }
}

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Q3404. Write code for the usage of Builder Design Pattern

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=964

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Q3405. Write code for constructor overloading

Core Java

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=965

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Q3406. Write code to check if an integer is odd or even using ternary operator

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=963

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Q3407. Write code to sort elements of a set

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=952

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Q3408. In the following code , how many methods needs to be implemented in Class B ?

public interface A{
   public void method1();
   public void method2();
   public void method3();
}

abstract class B implements A{
}

Core Java

Ans. As Class B has been declared abstract , we can either implement any of these methods and just declare rest of them abstract.

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Q3409. What will the following code print ?

Integer a = 100, b =100;
Integer c = 1000, d = 1000;
System.out.println(a == b);
System.out.println(c ==d);

Core Java

Ans. false
false

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Recently asked in Capital One.

Q3410. What will happen if we call perform(null) ?

public void perform(Object obj) {
System.out.println("Object");
}

public void perform(Integer int) {
System.out.println("Integer");
}

Core Java

Ans. compiler will throws error as ambiguous methods

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Q3411. 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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Q3412. In which cases , moving methods to utility class could be useful ?

Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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Q3413. Write a program for Coin Changer application ?

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=979

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Q3414. What will be the output of following code ?

System.out.println((int)'a');

Ans. The ascii value of a i.e 97

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Q3415. What will be the output of

System.out.println((Integer)'a');

Ans. It will result in compilation error as primitive char cannot be casted to Integer object, alternatively we can cast it to primitive int like following

System.out.println((int)'a');

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Q3416. What are the new classes in JDK 1.9 ( Java 9 ) ?

Ans. http://www.buggybread.com/2015/05/java-9-new-classes-and-interfaces-in.html

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Q3417. What is unmodifiable set / unmodifiable map ? How can we create one ?

Ans. It is an unmodifiable / read only view of the underlying collection. We can use

Collections.unmodifiableSet(Set set)
Collections.unmodifiableMap(Map map)
Collections.unmodifiableCollection(Collection collection)

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Q3418. What is the use of MethodHandle ?

Ans. MethodHandle is a modern, more flexible, more typesafe way of doing reflection.

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Q3419. 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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Q3420. What are JSP Scriptlets?

Ans. Scriptlet allow to write Java code inside JSP like following

<% Java Code %>

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