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

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Q851. How different is it when final applied to variables and object references ?

Ans. final when assigned to object references doesn't make them immutable. It means that the references cannot be de-referenced.

final when applied to variables means that the value cannot be changed.

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Q852. Why the following code produced this output ?

int x = 5;
int y = x;
y = 10;

System.out.println(x); // prints 5 and not 10

Core Java

Ans. Because when we say y = x, the value of x is copied to another memory location and then y points to that new memory location.

Unlike object references that once assigned point to same object in memory, value is copied in case of variable assignment.

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Q853. In which memory segment - heap or stack, the following stored by JVM

1. static members
2. objects
3. object references
4. local or method variables

Core Java

Ans. static members are stored in method area of heap

objects are stored on heap

object references are stored on stack

local or method variables are stored on stack

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Q854. How can we convert String into Char array and vice versa ?

Core Java

Ans. There is a method toCharArray() within String class that can be used to convert string to char array.

string.toCharArray();

String class has an argument constructor that takes a char array and create a string

new String(charArray);

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Q855. How can we convert a character or a character array into a String ?

Core Java

Ans. String has an argument constructor that take char array as argument and creates a string.

There is no constructor available with String that takes in a character and creates a String. We can use StringBuilder which has a char argument constructor.

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Q856. Explain Generics in Java ?

Core Java

Ans. Generics are a facility of generic programming that were added to the Java programming language in 2004 within J2SE5.0. They allow "a type or method to operate on objects of various types while providing compile-time type safety.

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Q857. What are the uses of Abstraction ?

Core Java

Ans. Loose Coupling
Facilitates designing complex applications by making them modular.

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Q858. Why is JVM called Virtual machine ?

Core Java

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Q859. Lets say we have a set "set1" with objects of Class A, Class has a non static string called element1, Write a code ( using lambda expression ) to see if there is any object in the set with element1 = "Hello".

Core Java

Ans. set1.stream().filter(p->p.element1.equals("Hello")).findAny().isPreent();

or

set1.stream().map(A::getElement1).anyMatch("Hello"::equals)

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Q860. Is Runtime Polymorphism possible without Inheritance ?

Core Java

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q861. Why is Java such an important Programming language ?

Core Java

Ans. Because of following features

Object Oriented and hence helps build maintainable and easily enhanceable code.
Platform Independence and hence can be executed anywhere
Fast due to JIT compiler

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Q862. Why Java is considered more purer object oriented language than C++ ?

Core Java

Ans. Because of

lack of use of pointers,
Lack of structural programming and
Lack of Multiple Inheritance

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Q863. Does Wrapper classes produces immutable objects ?

Core Java

Ans. Yes

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Q864. 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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Q865. 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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Q866. 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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Q867. 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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Q868. In case of generic class declared like following , What can T hold

class MyClass<T>{
T element;
}

Core Java

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Q869. What features would you like to see in Java 10 ?

Core Java

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Q870. Can we instantiate the object of derived class if parent constructor is private ?

Core Java

Ans. No

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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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