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The most popular programming language used today in the IT sector is Java. A Java Support Engineer, also known as a Java Technical Support Engineer, is responsible for understanding code and being able to design technical solutions. They provide optimal solutions for basic problems, code fixes, and data modifications and diagnose and fix operational problems.

As a Java Support Engineer, you must work closely with the support and operations teams to assist them and increase customer satisfaction. In this role, you will need to deeply understand the organization's products and architecture to deliver application enhancements.
In order to succeed in this position, you will also need to contact with executives and clients, so a candidate with strong communication skills is preferred.

Most Java support profile questions are from Core Java, Database, Networking, JDBC, and other related concepts. The same goal is served by this essay. Here is a comprehensive resource to assist you in answering the most typical Core Java Interview questions.

Java Interview Questions


1. Why is the Java language, platform independent?


The Java language was developed to be hardware and software-independent, as the compiler compiles the code and then converts it into platform-independent bytecode that can be run on multiple systems.
The only requirement for running this bytecode is that it has a runtime environment (JRE) installed.

2. Why is Java not purely an Object Oriented language?


Java offers byte, boolean, char, short, int, float, long, and double as primitive data types. As a result, it is not purely object-oriented.

3. Java's heap and stack memory differ from one another. and how Java employs it.


The area of memory that has been set aside for each distinct programme is known as stack memory. And it was fixed. On the other hand, heap memory is the part that has not been allocated to the java program but will be available for use when required, usually during the program's runtime.
Java uses this memory as -

" When we write a java program, all the variables, methods, etc., are stored in the stack memory.
" And when we create any object in the java program, that object is created in heap memory. And was referenced from stack memory.

4. How is Java different from C++?


" C++ is the only compiled language, while Java is compiled and interpreted language.
" Java programs are machine independent, while a c++ program can only run on the machine it is compiled on.
" C++ allows users to use pointers in a program. While Java does not allow this. Java uses pointers internally.
" C++ supports the concept of multiple inheritances, while Java does not. And it's because we avoid the complexity of the name ambiguity that causes the diamond problem.

5. Pointers are used in C/C++. Why doesn't Java use pointers?


Pointers are quite complex and dangerous for novice programmers. Java focuses on code simplicity, and using pointers can be challenging. Using a pointer can also cause potential errors. In addition, security is also compromised if pointers are used because users can directly access memory using pointers.

So a certain level of abstraction is provided by not including pointers in Java. Additionally, pointers can make the garbage collection process quite slow and error-prone. Java uses references because, unlike pointers, they cannot be manipulated.

6. What do you mean by an instance variable and a local variable?


Instance variables are those variables that are accessible by all methods in a class. They are declared outside the methods and inside the class. These variables describe the object's properties and remain bound to it at all costs.
All class objects will have their own copy of the variables to use. Suppose any modification is made to these variables. In that case, only this instance will be affected, and all other class instances will remain unaffected.

7. What is an abstraction in Java?


Abstraction refers to the quality of dealing with ideas rather than events. It basically deals with hiding the details and showing the essentials to the user. So it can be said that abstraction in Java hides implementation details from the user and exposes only the functionality. Abstraction can be achieved in two ways:

1. Abstract classes (0-100% abstraction can be achieved)
2. Interface (100% abstraction can be achieved)

8. What do you mean by the interface in Java?


An interface in Java is a class blueprint, or you can say it is a collection of abstract methods and static constants. Each method is public and abstract in an interface but contains no constructor. So an interface is essentially a group of related methods with empty bodies. Example:
public interface Animal {
 public void eat();
 public void sleep();
 public void run();
}

9. What is polymorphism?


Polymorphism is succinctly described as "one interface, many implementations". The capacity to give anything distinct meanings or uses in various contextsspecifically, allowing an entity like as a variable, function, or object to take on multiple formsis known as polymorphism. There are two types of polymorphism:
" Compile time polymorphism
" Runtime polymorphism
Compile-time polymorphism is method overloading, while runtime polymorphism uses inheritance and interfaces.

10. What are the different types of inheritance in Java?


Java allows the following three types of inheritance:
1. Single Inheritance: There is only one parent class and one child class in simple inheritance, meaning that one class simply inherits the properties of another.
2. Multilevel Inheritance: Multilevel inheritance is the process of deriving a class from another class that itself was descended from another class, i.e., a class with more than one parent class but descended from them at various levels.
3. Hierarchical Inheritance: A class is said to be hierarchical when it has more than one subclass, or more than one child class shares the same parent class, in other words.

11. What are method overloading and method overriding?


Method Overloading:
" Methods of the same class have the same name when using method overloading. Still, each method must have a different number of parameters or parameters with different types and order.
" Overloading a method means "adding" or "extending" more to the method's behavior.
" It's compile-time polymorphism.
" Methods must have a different signature.
" It may or may not require inheritance in method overloading.
Method Override:
" When a subclass overrides a method, it does so with the same name, number, and type of parameters as the superclass, as well as the same return type.
" Overriding a method means "Changing" the existing behavior of the method.
" It's runtime polymorphism.
" The methods must have the same signature.
" It always requires inheritance in the Overriding method.

12. What do you mean by aggregation?


An aggregation is a specialized association where each object has its own life cycle. Still, there is ownership, and a child object cannot belong to another parent object. Let's take the example of a department and a teacher. One teacher cannot belong to multiple departments. Still, if we delete the department teacher object, it will not be destroyed.

13. What is a composition in Java?


Again, the composition is a specialized form of aggregation, and we can call it a "death" relation. It is a powerful type of aggregation. A child object does not have its own life cycle; if the parent object is deleted, all the child objects will also be deleted. Let's take the example of the relationship between the house and the rooms again. A house can contain multiple rooms, no independent life of a room, and no room can belong to two different houses. If we delete a house, the room is automatically deleted.

14. What is Session Management in Java?


A session is a dynamic state of the random conversation between a client and a server. A virtual communication channel contains a chain of responses and requests from both sides. A popular way to implement session management is to create a session ID in the client-server communication discourse.

15. Briefly explain the term Spring Framework.


In essence, Spring is an inversion of control container and application framework for Java. The Spring framework uses Java to build enterprise applications. It's especially helpful to keep in mind that the Spring framework's key functionalities are essentially appropriate for any Java application.

16. How to handle exceptions in Spring MVC Framework?


Spring MVC has two approaches to handling exceptions:
" Exception handler method: The user receives the @ExceptionHandler annotation type, which is used to annotate the exception handling method in this style of exception handling.
" XML configuration: To map the exception, the user can use the SimpleMappingExceptionResolver object in the Spring application file.

17. What is JCA in Java?


The Java Cryptography Architecture provides a platform, architecture, and application programming interface that enables decryption and encryption.
Java Cryptography Architecture is used by developers to integrate security solutions into their applications. The Java Cryptography Architecture helps implement third-party security rules and regulations.
The Java Cryptography Architecture uses a hash table, message digest, etc., to implement security.

18. Explain JPA in Java.


The Java Persistence API allows us to create a persistence layer for desktop and web applications. Java Persistence deals with the following:
" Java Persistence API
" Query language
" Java Persistence Criteria API
" Object mapping metadata

19. What is the difference between systems.out, System.err, and System.in?


System.out and System.err represent the monitor by default and can therefore be used to send data or results to the monitor. System.out is used to display normal messages and results. System.err is used to display error messages. System.in represents an InputStream object, which by default represents a standard input device, i.e., a keyboard.

20. When can you use the keyword "super"?


The super keyword is basically used to denote a superclass. If the same fields are in both the parent and child classes, the super keyword can be used to access the data members of the parent class.

Conclusion


So this brings us to the end of the Java Questions blog. The topics you have learned in this Core Java Interview Questions blog are the most in-demand skill sets recruiters are looking for in a Java Professional. This set of Java Interview Questions will help you ace your job interview.