Java Interview Questions: Your Ultimate Guide to Level Up

 How well would you do in a Java interview? If you need assistance polishing your Java skills, we’re here to provide 15 Java Interview Questions. Let’s have a basic grasp of Java before we dive into questions.

To begin, what is Java?

In 1982, Java was created by James Gosling as a high-level programming language. With its object-oriented foundation, it’s ideal for creating complex software. 

In this article, you’ll find answers to the most commonly asked java interview questions, including those related to String Handling, Java 8, Java multithreading, Java OOPs, Java exception handling, Java collections, and more.

Studying the questions can improve your performance in the interviews. You should expect Java basic interview questions from the most elementary to the most complex levels.

There are many valuable Java interview questions and answers for both beginners and experienced applicants. We will learn about a few of the most commonly asked Java Interview Questions in this blog. 

Core Java Interview Questions

Core Java Basic Interview Questions
  1. What is the significance of Java, a platform-independent language?

The compiler of the Java programming language turns the source code into platform-independent bytecode, making the language itself independent of hardware and software.

If the system does not have a runtime environment installed, then the byte code won’t execute.

  1. What is the difference between Stack memory and Heap in Java, and how is this used in Java?

Stack memory defines the amount of memory allocated to each application. On the contrary hand, heap memory is not explicitly assigned to the Java code but is made accessible to the application at runtime.

  1. Describe the features of the Java programming language.

The Java programming language has the following features:

  • Java’s accessibility makes it a popular programming language. Java’s syntax is derived from C++, which facilitates software development.
  • Java’s object orientation enables us to store our code as a collection of data and action objects.
  • Java allows for a read-once, write-anywhere strategy, making it easily portable. The Java code will run on all of the computers. Bytecode (.class) is generated from the Java programme (.java) so that it may be readily executed on any computer.
  • Java can be used on any computer system since it was designed to be platform-independent. It’s not like C or C++, where you require a specific environment to run the code. Java comes with its platform for running programmes. 
  • Java’s lack of reliance on explicit pointers contributes to its security. 
  • Java is a reliable programming language because of the care it takes with its memory. It’s more secure because of ideas like automated garbage collection and exception handling.
  • Java does not care about the underlying architecture. Hence it is considered architecturally neutral. Java doesn’t have the concept of architecture-dependent data size as C does, where data sizes may change depending on the system’s bit depth (32 bits or 64 bits).
  • Compiler and interpreter: Java employs the Just-in-time (JIT) interpreter to run code at runtime.
  • High Performance: Java’s bytecode is “near” to native code. Hence it’s much quicker than other interpreted programming languages. Compared to a compiled language like C++, it is still sluggish.
  • Multithreaded: By creating many threads, we may make Java applications that handle various tasks simultaneously. Multi-primary threading’s benefit is that it eliminates the need to allocate separate memory pools for each thread. They use the same storage space for their data. Multimedia, web applications, etc., all benefit significantly from using lines.
  • Java’s distributed nature comes from making it easier for developers to build programmes that run on a network. When developing distributed applications, RMI and EJB are employed. With this Java capability, we may access files by invoking the corresponding methods on any computer connected to the internet, regardless of where those methods were initially used.
  • The Java language is very dynamic. Classes may be loaded dynamically. This implies that courses are only downloaded when necessary. In addition, it is compatible with the built-in features of C and C++, its parent languages.
  1. What do you mean by Java virtual machines?

The computer can execute Java programmes thanks to a virtual machine called Java Virtual Machine. The JVM is a virtual machine that runs Java programmes by executing their primary function. The computer system must conform to the JVM standard. This is because the JVM compiles Java into a machine-independent form of bytecode that is very similar to the native language.

  1. Which differences exist between the Java Development Kit, the Java Runtime Environment, and the Java Virtual Machine?


The Java Virtual Machine (abbreviated to “JVM”) is an abstract processor that offers a runtime environment suitable for executing Java bytecode. The Java Virtual Machine Specification details the inner workings of the JVM. Oracle and others have developed the infrastructure necessary to run it. JRE is the name of the programme that runs this.

There are JVMs for a wide variety of systems. When we execute the Java class, we produce a new runtime instance. JVM consists of three key concepts: illustration, implementation, and specification.


The Java Runtime Environment is a collection of programmes needed to run Java programmes. It’s the thing that gives the runtime environment a chance to work. The Java Virtual Machine is being used here. The thing is real and can be touched and held. It includes the libraries and other files required for JVM to function.


A Java Development Kit, or JDK, is a set of Java-related tools. Java SE is a tool for software development for creating Java-based programmes and applets. In a physical sense, it is accurate. Software development tools and the Java Runtime Environment (JRE) are included. 

  1. In how many different ways does JVM allocate memory?

Class Area: Class Area maintains class-specific structures such as runtime constant pools, fields, method data, and method code.

Heap: Memory for objects is stored in this space, which is only accessible during runtime.

Stack: The Java Stack is where the frames are saved. A method’s context is where its variables are declared, partial results are stored and where its invocation and return are handled. A separate JVM stack is created alongside each thread. Each time a function is called, a new frame is produced. Once a method has been invoked on a stand, the structure is destroyed.

Data Counter Sequence: The instruction executed in a Java virtual machine may be found at the location stored in the PC (programme counter) register.

Native Method Stack: It has all the application’s native methods.

  1. What is a just-in-time compiler, or JIT?

JIT Compiler: Its purpose is to boost efficiency. By reducing the time required for compilation, JIT prioritises the simultaneous creation of bytecode sections that perform comparable tasks. A compiler, in this context, is a tool that converts Java programmes written for a JVM to native code for a particular CPU.

  1. What do you understand about ‘Platform’ in Java? 

When talking about the environment in which a programme runs, we refer to it as the platform. Platforms may either be software- or hardware-based. The platform used is software, and Java is what makes it possible.

You Must Watch: Learn Java: Master Object-Oriented Programming Concepts
  1. In what ways does the Java platform vary from others?

The Java platform differs from others in the following ways.

  • Java is a software platform, while other platforms may be hardware or software.
  • Java runs on different hardware platforms, which are limited to providing just the bare minimum of hardware components.
  1. What makes Java so versatile that code written in it can execute on any platform?

The bytecode makes Java versatile. The Java compiler creates a language between the machine and source code by translating Java programmes into class files (Byte Code). In other words, this bytecode is platform-independent and may be run on any machine.

  1. What is a classloader?

To access and execute class files, the Java Virtual Machine (JVM) relies on a component called the classloader. The class loader is invoked before the Java application is completed.

Java includes a total of three classloaders by default:

Bootstrap ClassLoader: The original classloader is the one that extends the classloader for Extension. It reads all the Java Standard Edition class files from the rt.jar file, which includes Java lang package classes, the package classes, the Java util package classes, the package classes, the java.sql package classes, and so on.

ClassLoader Plugin Update: This classloader is a descendant of Bootstrap and the parent of the System classloader. The jar files in the $JAVA HOME/JRE/lib/ext directory are read.

System/Application ClassLoader: This classloader is a descendant of the parent Extension classloader. It uses the classpath to read the necessary class files. The current working directory is used as the classpath by default. The “-cp” or “-classpath” option is used to modify the classpath. The term “Application classloader” is another name for it.

  1. What is the local variables’ default value?

There is no default value assigned to any of the local variables.

  1. What is composition?

Composition is the process through which one class is referenced inside another type. It is termed composition when one item comprises another, and the latter cannot exist independently of the former. Composition, therefore, is an instance of aggregation that emphasises a more robust connection between its constituent parts. For example, A group of students could make up a class. No education system can function without students. The rank and the students work together to form a cohesive whole.

  1. Can the static method be overridden?

The static methods cannot be overridden since they are intrinsic to the class and not the object.

  1.  What role does reflection play in Java?

It’s a runtime API that lets you see and modify how your classes, interfaces, and methods are acting. Using Java Reflection, you can examine a program’s class, protocols, variables, and functions during runtime despite knowing their names at compile time. It’s useful for making new objects, contacting methods, and reading and writing to fields.

These 15 practice questions and answers for a Java programming language interview will help you shine during the actual interview.

Java is a standard programming language found in every business’s infrastructure. Java interview questions and answers are essential if you want to succeed in your next Java developer or full-stack development interview and get your dream job.

These are core java interview questions that are regularly asked, so prepare for them and give your best shot in the following interview.

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