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

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Q461. What are annotations and what are it's advantages ?

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Q462. 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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Q463. What is the use of Object class ?

Core Java

Ans. 1. Default definition for some of the methods , like equals, hashcode etc that gets carried to all objects even if you don't define anything. But that default definition is kind of like assigning 0 to integer, it just provide a safe state , nothing much for comparison.

2. Places where you have no idea about what object you may receive and just want to perform out of 8 basic methods of object class, something like printing their string representation ( defined by their toString method ), or equality ( using their equals method )

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Q464. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

Core Java

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Q465. 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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Q466. 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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Q467. What is a BlockingQueue ?

Core Java

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Q468. Do we have sorted collection for List ?

Core Java

Ans. Not in java.util

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Q469. How can we ensure thread safety in static method ?

Core Java

Ans. By using synchronized static method or synchronized block

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Q470. 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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Q471. 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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Q472. What is the difference between uninitialized values for primitive types and Wrapper classes ?

Core Java

Ans. When we create reference for primitive type, it's memory is allocated. So even if we don't assign any value to it, the default value is initialized.

int x; // default value 0 initialized

But for object references, it's different as references hold nothing till an object is assigned.

Object obj; // contains null

So all primitive types when declared , contains their respective default values on the basis of their type whereas all wrapper class References contains null irrespective of their types.

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Q473. 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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Q474. What are the benefits of using Wrapper classes over primitive types ?

Core Java

Ans. With Collection classes , we cannot use primitive types. Moreover for any class using generic types, we cannot use primitive types.

They add more functionality by means of additional methods.

As their reference can be null , they offer consistent check for uninitialized state.

They facilitate caching and reuse by means of constant Pools.

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Q475. 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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Q476. Why can we have a static inner class but not a static Top level class in Java ?

Core Java

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Q477. Why do we use Thread Class as well as Runnable Interface for creating threads in Java ?

Core Java

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Q478. 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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Q479. 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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Q480. 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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Q481. 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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Q482. Can we have a sub enum within an enum ?

Core Java

Ans. Yes

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Q483. Can an enum extend another enum ?

Core Java

Ans. No

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Q484. Can we instantiate the object of derived class if parent constructor is private ?

Core Java

Ans. No

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Q485. What features would you like to see in Java 10 ?

Core Java

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Q486. In case of generic class declared like following , What can T hold

class MyClass<T>{
T element;
}

Core Java

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Q487. Which of the two - iteration or recursion - is slower ?

Core Java

Ans. Any function call is slower than the code in the same method as Java has to maintain stack of meta and function call information. So recursion is slower.

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Q488. In the following code, which text will get printed immediately after Hello

for(int countx=0;countx<10;count++){
System.out.println("World");
for(int countx=0;countx<10;count++){
System.out.println("Friend");
for(int countx=0;countx<10;count++){
System.out.println("Hello");
break;
}
System.out.println("Buddy");
}
}

Core Java

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Q489. What do we mean by a Data Type ?

Core Java

Ans. if you have similar type of data or objects or entities, then we can give them a type with unique name. And this name will be our Data type.

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Q490. Why shouldn't we use string concatenation extensively or in a loop ?

Core Java

Ans. Because String being an immutable object creates a new object upon each concatenation cycle. If there is any such need , we should use String Builder whose objects are mutable.

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