Java Developer Realtime Interview Questions & Answers

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Table of Contents

No.	Questions
	Core
1	Write an implementation for this funtional interface?
2	Difference between map and flatmap in Java 8?
	Logical
1	Reverse this array without new array.

Core

1. Write an implementation for this funtional interface?

   public interface functionalInterface {
      void read(int a);
   }

   public class FunctionalInterfaceImpl {
       public static void main(String[] args) {
           functionalInterface f = (a) -> System.out.println("Value is: " + a);
           f.read(10);
       }
   }

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2. Difference between map and flatmap in Java 8?

   In Java 8, map and flatMap are both methods in the Stream interface used for transforming elements.

   • map: The map method transforms each element of a stream into another object using the provided function. It applies the function to each element of the stream independently and returns a new stream containing the transformed elements.

     List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
     List<Integer> mapResult = list.stream().map(x -> x * 2).collect(Collectors.toList());
     System.out.println(mapResult); // prints [2, 4, 6, 8, 10]

   • flatMap: The flatMap method transforms each element of a stream into a stream of objects and then combines all the streams into a single stream. It is useful when we want to flatten a stream of collections or arrays into a single stream of elements.

     List<List<Integer>> list = Arrays.asList(Arrays.asList(1, 2), Arrays.asList(3, 4), Arrays.asList(5, 6));
     List<Integer> flatMapResult = list.stream().flatMap(Collection::stream).collect(Collectors.toList());
     System.out.println(flatMapResult); // prints [1, 2, 3, 4, 5, 6]

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Logical

1. Reverse this array without new array.

   Input: { 2,9,4,7,1,6 }

   public class ReverseArray {
       public static void main(String[] args) {
           int[] arr = { 2, 9, 4, 7, 1, 6 };
           System.out.println("Before: " + Arrays.toString(arr));
           for (int i = 0; i < arr.length / 2; i++) {
               int temp = arr[i];
               arr[i] = arr[arr.length - 1 - i];
               arr[arr.length - 1 - i] = temp;
           }
           System.out.println("After: " + Arrays.toString(arr));
       }
   }

   Output:

   Before: [2, 9, 4, 7, 1, 6]
   After: [6, 1, 7, 4, 9, 2]
   

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