Java Interview Question & Answers
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Frequently Asked Java Interview Questions & Answers

Java is the most famous programming language in the IT enterprise nowadays. The main motive for a massive range of beginners and professionals inside the field of programming is the capability of professional opportunities for Java knowledge and java interview questions plays very crucial role . This text is dedicated to the identical purpose. This is a complete manual on how to clear up the most regularly requested Java interview questions and answers.

Java Interview Questions

1. What is Java ?

Java is an object-orientated programming language that creates software programs for more than one platform. while a programmer creates a Java utility, the compiled code (known as byte code) runs on maximum working systems (OS) consisting of windows, Linux, and Mac OS. Java derives a whole lot of its syntax from the C and C ++ programming languages. 

 Java was developed in the mid-1990s by former Sun Microsystems computer scientists James A. Gosling, Mike Sheridan, and Patrick Naughton.

2. Tell us about the top 5 features of Java ?

The pinnacle 5 features of the Java programming language might be: 

Easy: Java is straightforward to examine. The Java syntax is based on C ++, which makes it less difficult to put in writing applications in Java. 

Object-orientated: Java follows an object-orientated paradigm. This allows you to manage your code as a combination of different object sorts, which include both facts and behavior.

Transportable: Java supports the read-as soon as-write-everywhere technique. Java applications may be run on any system. Java applications (.java) are transformed to bytecode (.class) that runs smoothly on any gadget. 

Platform-unbiased: Java is a platform-impartial programming language. that is unlike other programming languages together with C and C ++ that require a platform to run. Java comes with a platform for executing code. Java is unbiased of the operating system it runs on. 

 Secured: Java is blanketed because it does not use express hints. Java additionally gives the idea of Bytecode and exception handling, making it comfier.

3. Tell me how Java is different from C++ ?

C++ is derived from C and has the capabilities of each procedural and object-orientated programming language. C++ turned into designed for utility and System development.

Java is built on a virtual machine. This is very safe to see nature and very visible. Grouping is grouped with a comprehensive library to support existing platform abstraction. 

Java is mainly developed for application programming and has an interpreter function for printing systems and was later developed on a network computer.

4. Why Java does not use any pointers like C++?

Pointers are very complex and unsafe to use by novice programmers. Java focuses on the simplicity of the code, and using pointers can make it difficult. Using pointers can also lead to potential bugs. In addition, pointers allow users to access memory directly, which reduces security. 

 Therefore, not including pointers in Java provides some abstraction. In addition, using pointers can significantly slow down the garbage collection process and cause bugs. Java uses references. This is because, unlike pointers, you can’t manipulate references.

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5. Tell us about the common applications of Java Programming Languages ?

Java’s popularity is due to its platform independence. Whether Java is installed on a Windows, Linux, or Unix desktop PC, Macintosh computer, smartphone, or mainframe computer, only the Java Runtime Environment (JRE) installation works. 

Here are some common places where Java is displayed.

Android applications: 

Maximum Android applications use the Java API or are written in Java, so Java is often considered the authentic programming language for mobile app development. 

Laptop GUI packages: 

Many computing device applications are developed in Java. Swing, the Abstract Windowing Toolkit (AWT), and JavaFX are the key equipment for facilitating GUI development. 

Internet-based packages: 

Java is extensively used to develop an extensive range of interactive websites and web-based programs located in the areas of coverage, social security, training, and health. 

Economic and Retail services: 

Java is used to create transaction control and billing applications in addition to server-aspect applications. Science and research: Java is the desired language of the clinical network for a spread of mathematical calculations and different medical operations. Utilized by MATLAB and the Hadoop MapReduce framework, it can take care of huge datasets and huge statistics technologies.

6. Tell us about the Java Virtual Machine?

A Java virtual machine is a virtual machine that allows a computer to run Java programs. The JVM acts like a run-time engine that calls the main method that exists in Java code. The JVM is a specification that needs to be implemented in a computer system. The Java code is compiled by the JVM into machine-independent bytecode that is close to native code.

7. Tell us about the JIT Compiler?

Used to enhance overall performance. JIT compiles bytecode with comparable capability at an equal time, reducing the time required to collect. Here, the term “compiler” refers to a translator from the Java virtual machine (JVM) training set to a selected CPU instructing set.

8. How Java is different than the other platforms?

The primary differences between the Java platform and other platforms are: 

  • Java is a software-based platform, but other platforms can be hardware 
  • or software-based platforms
  • Java runs on other hardware platforms, but other platforms can only have hardware components

9. What do you know about Instance variables and Local Variables?

Instance variables are variables that can be accessed by all methods in the class. They are declared outside the method and inside the class. These variables describe the properties of the object and remain bound to the object at all costs. 

Every object in the class has a copy of the variables it uses. Any changes to these variables will affect only this instance, not all other class instances.

A local variable is a variable that resides in a block, function, or constructor and can only be accessed from within that variable. The use of variables is limited to the block area. Whenever a local variable is declared within a method, other class methods are unaware of the local variable.

Java Interview Questions for Experienced Candidates

10. How do you use the Final Keyword?

In Java, the final keyword is used to define something like a constant/final and represents an inaccessible modifier. 

Final variable: 

 If the variable is declared as final in Java, you cannot change the value after the assignment. If this variable has no value assigned, it can only be assigned by the class’s constructor. 

Final method: 

Methods declared as final cannot be overridden by their child classes. You cannot mark a constructor as final because the constructor is not inherited whenever the class is inherited.

Therefore, it makes no sense to mark it as final. Java throws a compile error indicating that the last modifier is not allowed here 

Final class: 

You cannot inherit a class from a category declared as very last. But, this final magnificence can be prolonged to other classes.

11. Are you aware of the super keyword?

The super keyword is used to get admission to hidden fields and overridden strategies or attributes of super classes.  Access to the data members of the parent class when the class and its child subclasses have the same member name. 

 To call the default parameterized constructor of the parent class from within the child class. 

Access to the methods of the parent class if the child class overrides them.

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12. Is it possible to override the static methods in Java?

No, it is not. The declarations of static methods with the same signature can be executed in subclasses, but in such cases, run-time polymorphism cannot be performed. 

 Overrides or dynamic polymorphism occur at run time, but static methods are loaded and statically looked up at compile time. Therefore, you cannot override these methods.

13. What do you know about the “Garbage Collection”?

The main goal of this process is to free up memory occupied by unwanted and unreachable objects by removing these unreachable objects while the Java program is running. 

 This guarantees efficient use of memory resources but does not guarantee that you have enough memory to run your program.

14. Tell me the difference between Staring, StringBuffer, and StringBuilder ?

Storage Capacity: 

For strings, the string pool acts as a memory area. For StringBuilder and StringBuffer, heap memory is a memory area. Variability: The string is immutable, but both StringBuilder and StringBuffer are variable. 


Manipulating strings is fairly slow. However, StringBuilder is the fastest to perform operations. StringBuffer is faster than String and slower than StringBuilder. (For example, adding a character is the fastest in StringBuilder and very slow in String, because the new string to which the character is added requires new memory.) 


For threaded environments, StringBuilder and StringBuffer are used, but String is not. However, StringBuilder is suitable for single-threaded environments, and StringBuffer is suitable for multiple threads.

15. Why “Reflection” is important in Java?

The term reflection is used to describe the function of code that inspects other code from the code itself or its system and modifies the code at run time. 

 Consider an example of an object of unknown type and a method “fooBar ()” that needs to be called on the object. Java’s static typing system does not allow this method call unless the object’s type is known in advance. This can be achieved by reflection. This allows the code to scan the object, identify if there is a method called fooBar (), and call the method only when needed.

The use of reflection has its drawbacks. 


Method calls with reflection are about three times slower than direct method calls. 

Type Safety:

If a method is incorrectly called by a reference using reflection, the call will fail at run time because it will not be recognized at compile/load time. 


Every time a reflection method fails, it’s very difficult to find the root cause of the failure due to the huge stack trace. You need to dig deeper into the logs of the invoke () and proxy () methods to determine the root cause. 

Therefore, it is advisable to pursue a solution without reflection and use this method as a last resort.

16. Are you aware of the packages in Java?

Defining packages in Java has several advantages:

  • The package avoids name conflicts
  • This package provides easier access control
  • You can also create hidden classes that are not visible to the outside world and are not used in the package
  • Finding related classes is easy

17. What is an “Object” in Java?

An object is a real-time entity with several states and behaviors. In Java, an object is an instance of a class, and instance variables such as the state and methods of the object are used as the behavior of the object. Objects of the class can be created using the new keyword.

Tell me about the “Object-oriented Paradigm”

This is a programming paradigm based on objects defined in the class to which the data and methods belong. The object-oriented paradigm aims to incorporate the benefits of modularity and reusability. Objects are instances of classes that interact to design applications and programs.

  • We take a bottom-up approach to program design. Focus on the data using methods that manipulate the data of the object 
  • It includes concepts such as encapsulation and abstraction that hide complexity from the user and show only functionality.
  • Implement real-time approaches such as inheritance and abstraction.
  • Examples of object-oriented paradigms include C ++, Simula, Smalltalk, Python, and C #.

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18. Explain Object-oriented Programming Vs Object-based Programming ?

There are the following basic differences between object-oriented and object-based languages: 

 Object-oriented languages ​​follow all the concepts of OOP, but object-based languages ​​do not follow all the concepts of OOP, such as inheritance and polymorphism. 

 Object-oriented languages ​​have no built-in objects, while object-based languages ​​have built-in objects. For example, JavaScript has a widget. 

 Examples of object-oriented programming are Java, C #, Smalltalk, etc., while examples of object-based languages ​​are JavaScript, VBScript, etc.

19. Tell me about the Constructor and how it is used in Java?

The constructor can be defined as a special type of method that initializes the object’s state. Called when the class is instantiated and memory is assigned to the object. Every time an object is created with a new keyword, a class standard constructor is called. The constructor’s name must be similar to the class name. The constructor may not have an explicit yield type.

There are two types of constructors in Java, based on the parameters passed in the constructor. 

Default constructor: 

The default constructor takes no value. The default constructor is primarily used to initialize instance variables with default values. It can also be used to perform some useful object creation tasks. If no constructor is defined in the class, the default constructor is implicitly called by the compiler. 

Parameterized constructor: 

A parameterized constructor is a constructor that can initialize an instance variable with a specified value. That is, a constructor that can accept arguments is called a parameterized constructor.

20. Advantages of Java Programming Language?

Java produces applets (browser executables) that facilitate the interaction of objects with graphical user interfaces (GUIs) by Internet users. Before the advent of Java applets, web pages were usually static and non-interactive. Java applets have lost popularity with the release of competing products such as Adobe Flash and Microsoft Silverlight. 

Java applets run in a web browser using the Java Virtual Machine (JVM). This translates Java bytecode into native processor instructions, allowing indirect execution of operating system or platform programs. The JVM provides most of the components needed to execute bytecode. Bytecode is usually smaller than an executable program written in another programming language. Bytecode will fail to execute if the system does not have the required JVM. 

 To develop Java programs, you need the Java Software Development Kit (SDK). This typically includes compilers, interpreters, document generators, and other tools used to build complete applications. 

 You can reduce your development time by using an integrated development environment (IDE) such as JBuilder, Netbeans, Eclipse, or JCreator. The IDE makes it easy to develop GUIs that include buttons, text boxes, panels, frames, scrollbars, and other objects using drag-and-drop and point-and-click actions.

Above 20 Frequently asked java interview questions asked in MNC Interview. These java interview questions are prepared with consultation with Java Developers , Senior Java Developer , Java Project Manager.

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