1. Define Java

Java is a general-purpose, Object-oriented programming and most widely used language which was developed by James gosling in 1990s. It’s system independent language where one can run the compiled byte code in any other system which contains JRE in it.

2. Explain Features of Java

The features of Java include

Platform Independent – The byte code generated on one computer can run on another system.

Robust – Can easily handle errors during execution.

Multithreaded – IT enables users to write programs that can perform many tasks at a time.

Object Oriented – As we know everything in java is an Object.

Performance – Inclusion of JIT Compilers in JRE increases their performance than other programming languages.

3. Define Variable in Java and their types.

Variables are the storage locations which are used to store different types of data. In java there are three types of variables based on their scope. They are

Local Variables – These are the variables that are declared inside a method

Static Variables – These are the variables when one want to initialize them when the execution of program starts. They are defined using static keyword.

Instance Variables – These are defined outside methods but inside class.

4. Difference between JDK, JRE and JVM.

JDK (Java Development Kit) is a Software Development Environment which is used for developing java programs. JRE (Java Runtime Environment) is a space which enables users to execute java programs and JVM (Java Virtual Machine) is responsible for providing the runtime environment in which java compiler generated byte code can be executed.

5. What is meant by JIT Compiler? Define its usage

JIT (Just In Time) Compiler is responsible for compiling code at runtime instead of compiling it during the compile time of the programs (also known as Ahead-Of-Time). It improves the performance of java programs by compiling the generated byte code into machine code at run time.

6. Wrapper classes in Java

The main objective of introducing wrapper classes is when one want to convert primitive data types to object types and vice versa. There are some cases where util package handles only objects then we need to convert the primitive types to objects using these wrapper classes. The wrapper class for int is Integer, char Character, double-Double etc.

7. What are various access specifiers in Java?

In general access specifiers when we want to restrict the usage of variables under scope. Mainly There are three access specifiers in java. They are

Public – These members can be accessible everywhere in the program.

Private – These members are accessible only inside the class.

Protected – These members can be accessible outside package only with the help of child class.

8. Why the main method in Java is declared as static?

In java the static method is the one which is going to created inside the memory even before initializing the instance(object) of it. So, as we all know that in java the execution starts from the main method, we need to make sure that the main methods is called first with the help of declaring it as static method.

9. Is it possible to execute a Java program without main method?

Yes, we can execute java program without main method up to JDK 6 by initializing the static block but from JDK version 7 it’s mandatory to include main method in java program because the JVM finds for main() method in the program first.

10. Method Overloading in Java?

The process of writing the same method in different ways in a single program is known as Method Overloading in Java. The method can be overloaded in two ways in java one is by changing the number of arguments we are going to pass to that functions and another way is to change the data type of the arguments.

11. Final keyword and it’s usage in Java?

Final keyword in java is used when we want to make sure that the state/value of the variable or object Shouldn’t be changes once it’s initialized. So, when final keyword is used in declaration of class then no inheritance is possible, if we declare a method using final keyword then that method cannot be overridden and finally the final variable cannot be changed once it was initialized.

12. Is Java pure object-oriented language?

No, the Java is not a pure object-oriented language. The existence of primitive data types in java language makes it as True Object-oriented language instead of Pure because the primitive data type literals are considered as values not as objects so to convert them to objects, they introduced wrapper classes.

13. Constructors and it’s types in Java.

Constructors are special methods in java which are invoked when an object is created instead of explicitly calling like general methods. There are three types of constructors in java

Default Constructor

No argument Constructor

Parameterized Constructor

14. Explain Singleton class in Java.

As the name indicates singleton class in java refers to a class that can have a maximum of only one instance (object). The main purpose of introducing them is to restrict the creation of objects.

15. Is Java object-oriented or object-based language? Justify your answer?

Java is an object-oriented language because it’s capable of implementing all OOPS concepts when it comes to object-based languages the objects are pre-defined in them instead of creating them explicitly we’ll simply use them. JavaScript is a good example of Object based language because even though it has the concept of object but can’t be able to implement OOPS concepts as Java.