Core Java - Interview Questions and Answers for 'Core java' | Search Interview Question

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Q871. Can an enum extend another enum ?

Core Java

Ans. No

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Q872. Can we have a sub enum within an enum ?

Core Java

Ans. Yes

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Q873. If a Map needs to be accessed simultaneously by multiple threads, which collection class should be used ?

Core Java

Ans. ConcurrentHashMap

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Q874. Given a collection of Employee objects, how can we get the customers with name starting with 'A' using lambda expression.

Core Java

Ans. List emp = Arrays.asList("American", "Indian", "Finn");
emp.stream().filter(em -> em.startsWith("A")).forEach(System.out.println);

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Q875. What is the difference between stream and parallel stream ?

Core Java

Ans. streams are used for sequential processing of data and parallel streams are used for parallel processing of data (only if the underlying processor is multicore).

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Q876. What are the advantage of Abstract classes over interfaces with respect to Java 7 ? and What changed in Java 8 to help facilitate that in Java 8 ?

Core Java

Ans. Abstract Classes provide default implementations of methods that are inherited by the classes that extend them, which was not the case for Interfaces. This changed in Java 8, where default implementations are provided for methods.

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Q877. Why do we use Thread Class as well as Runnable Interface for creating threads in Java ?

Core Java

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Q878. Why can we have a static inner class but not a static Top level class in Java ?

Core Java

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Q879. Write a Program to print fibonacci series using recursion.

Core Java

Ans. public class FibonacciUsingRecursion {
   public static void main(String[] args) throws IOException{
      getNextFibanocci(1,1);
   }

   static int getNextFibanocci(int a,int b){
      if(a+b >= 100){
         return 0;
      } else {
         System.out.println(a+b);
         getNextFibanocci(b,a+b);
      }

      return 0;
   }
}

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Q880. Can we use primitive types with Collection classes ?

Core Java

Ans. No, As collection classes involve use of Generics, they cannot accept primitive types.

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Q881. Is immutability an advantage with Wrapper classes over primitive types ?

Core Java

Ans. There is no concept of de referencing with primitive types and hence they are implicitly immutable. Having wrapper classes as mutable offers disadvantages compared to primitive types. Wrapper classes being immutable offer similar advantage as primitive types.It actually overshadows the disadvantage wrapper class could have if they are immutable.

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Q882. Do we have Integer constant pool of primitive int or Integer objects ?

Core Java

Ans. It's of Integer objects and not primitive int.

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Q883. Which objects are eligible for garbage collection ?

Core Java

Ans. Objects that have lost their reference i.e. they cannot be accessed/used by the program anymore.

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Q884. Do we have sorted collection for List ?

Core Java

Ans. Not in java.util

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Q885. What is a BlockingQueue ?

Core Java

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Q886. Which immutable classes have you worked with ? Can you name some immutable Collections ? How to make an immutable collection ?

Core Java

Ans. string and wrapper class objects

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Q887. What are the benefits of immutability or Immutable classes ?

Core Java

Ans. Immutable objects are thread-safe so you will not have any synchronization issues.Immutable objects are good for Map keys and Set elements, since these typically do not change once created.Immutability makes it easier to write, use and reason about the code (class invariant is established once and then unchanged)Immutability makes it easier to parallelize your program as there are no conflicts among objects.The internal state of your program will be consistent even if you have exceptions.References to immutable objects can be cached as they are not going to change.

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Q888. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

Core Java

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Q889. How ConcurrentHashMap provides better performance compared to HashTable ?

Core Java

Ans. ConcurrentHashMap uses multiple buckets to store Data and hence avoid read locks which facilitates better performance.

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Q890. What are annotations and what are it's advantages ?

Core Java

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Q891. Suppose we have a string "Java is object oriented language" and we have to reverse every alternate word in string. How would we do that using Java program.

Core Java

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Q892. How to convert array to list in Java ?

Core Java

Ans. We can use Arrays.asList

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Q893. How much by default filling ratio in HashMap ?

Core Java

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Q894. Can we override wait() or notify() ?

Core Java

Ans. No, because these are final.

public final void wait() throws InterruptedException

public final void notify()

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Q895. What is a double ended queue?

Core Java

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Q896. A Kid can go up 1, 2 or 3 stairs in one step. Write a method that takes number of steps in a stair will print all possible ways he can take.

For example , printAllCombinations(3) should print

111
12
21
3

Similarly , printAllCombinations(4) should print

1111
121
13
211
22
31
4

Core Java

Ans. public static String findStep(int n) {
if (n == 1 || n == 0)
return 1;
else if (n == 2)
return 2;
else
return findStep(n - 3) + findStep(n - 2) + findStep(n - 1);
}

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Q897. Write a method that takes an integer and verifies if the number is power of 10.

Core Java

Ans. public static boolean isPowerOfTen(long input) {

if (input % 10 != 0 || input == 0) {
return false;
}

if (input == 10) {
return true;
}

return isPowerOfTen(input/10);
}

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Q898. What is the default data type of state variables in Clonable interface and Serializable interface ?

Core Java

Ans. Cloneable and Serializable are Marker Interfaces, So these are empty interfaces with no variables.

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Q899. How can i split a linked list in two parts in java 8?

Core Java

Ans. This can be done using a Spliterator.

LinkedList list = Arrays.asList("names","numbs","birds","animals");
Spliterator split1 = list.Spliterator();
Spliterator split2 = split1.Spliterator();

Now, the LinkedList is split into split1 and split2.
use split2 first then split1 to check the output.

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Q900. how does abstraction help your application ?

Core Java

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