Top 15+ Core Java Interview questions and answers on Java Basics in 2023

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Last updated : February 3, 2023

Welcome to our blog post on the top 15+ Core Java Interview Questions and Answers on Java Basics! In this post, we will be covering some of the most frequently asked questions about the Java programming language basic features in technical interviews. These questions will focus on the basic concepts and features of Java, such as JRE, JVM, JDK, platform independence, JIT compiler and much more.

Whether you are an experienced Java developer looking to brush up on your skills or a beginner looking to learn more about the language, this post is for you. We will be providing clear and concise answers to each question, along with examples to help you better understand the concepts being discussed.

So, without further ado, let’s dive in and start exploring the top 15+ Core Java Interview Questions and Answers on Java Basics!

Core Java Interview questions and answers on Java Basics

What is Java?

Java is a high-level, object-oriented programming language that was developed by Sun Microsystems (now owned by Oracle) in the mid-1990s. It is widely used for building standalone applications, applets, and web-based applications.

What is WORA in Java?

The most important feature of Java is its ability to run on any device or platform that supports Java without the need for recompilation. This is made possible by the use of the Java Virtual Machine (JVM), which interprets Java bytecode into machine code that can be executed on the target device. This feature, known as “write once, run anywhere” (WORA), makes Java code highly portable.

What are the most important features of Java other than platform independence?

  • In addition to platform independence, there are several other important features of the Java programming language:
  • Object-oriented programming: Java is a fully object-oriented language, which means that it supports the use of objects and classes to organize and structure code. This makes it easier to build complex, modular applications, as it allows developers to create reusable components that can be easily combined and customized.
  • Automatic memory management: Java has an automatic garbage collection feature that is responsible for allocating and deallocating memory as needed. This helps to prevent common memory-related errors, such as memory leaks and segmentation faults, and it makes Java code easier to write and maintain.
  • Security: Java has a number of built-in security features that help to protect against malicious code and protect the privacy of users. For example, Java has a security manager that is responsible for enforcing security policies, and it has a number of built-in cryptographic libraries that can be used to secure data.
  • Concurrency: Java supports the concept of concurrency, which means that it is possible to write programs that can execute multiple tasks concurrently. This is achieved through the use of threads, which are lightweight units of execution that can be created and managed by the JVM.
  • Portability: As mentioned earlier, Java is a platform-independent language, which means that Java code can run on any device that has a JVM. This makes it easy to deploy Java applications on a wide variety of platforms and environments.

Overall, these features make Java a powerful and widely used programming language that is suitable for a wide range of applications.

What are the main benefits of using Java?

Some of the main benefits of using Java include:

  • It is simple, easy to learn, and easy to use
  • It is object-oriented, which makes it a good choice for developing object-oriented software
  • It is platform-independent, so Java code can run on any device that has a JVM
  • It has a large and active developer community, which means that there are many resources available for learning and troubleshooting
  • It has excellent documentation and a vast array of libraries and frameworks

What are some characteristics of Java?

Some characteristics of Java include:

  • It is a class-based, object-oriented programming language
  • It is portable, meaning that Java code can run on any device that has a Java Virtual Machine (JVM)
  • It is platform-independent, meaning that Java code can run on any operating system
  • It is secure, as it has a number of features that help protect against viruses and other malicious software
  • It is simple and easy to learn, with a syntax that is similar to C++
  • It has a large and active developer community, with many resources available for learning and troubleshooting

What are some common uses of Java?

Java is commonly used for building standalone applications, applets, and web-based applications. It is also used for developing Android mobile applications, as well as for building server-side components of web applications.

Is Java a compiled or interpreted language?

Java is a compiled language, meaning that it is transformed into machine code that can be executed by a computer. However, the process of compiling Java code is different from the process of compiling other languages, such as C++. In Java, source code is compiled into an intermediate form called bytecode, which can then be run on any device that has a JVM.

Is Java a statically-typed or dynamically-typed language?

Java is a statically-typed language, meaning that the type of a variable must be specified at the time it is declared. This allows the compiler to catch type-related errors before the code is executed, which can help improve the reliability and maintainability of the code.

What is the Java Virtual Machine (JVM)?

The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs. It is responsible for interpreting Java bytecode and executing it on the computer. The JVM is what allows Java code to be portable, as it ensures that the code can run on any device that has a JVM, regardless of the underlying hardware and operating system.

What is the Java Development Kit (JDK)?

The Java Development Kit (JDK) is a software development kit that is used for developing Java applications. It includes tools for compiling, debugging, and running Java code, as well as a number of other useful tools and libraries. The JDK is available for free from Oracle, and it is an essential tool for any Java developer.

What is the difference between the JDK and the JRE?

The Java Development Kit (JDK) is a software development kit that is used for developing Java applications, while the Java Runtime Environment (JRE) is a standalone runtime environment that is used for running Java applications. The JDK includes the JRE, as well as a number of other tools and libraries that are needed for developing Java applications. In other words, the JDK is a superset of the JRE, and it is needed for development purposes, while the JRE is only needed for running Java applications.

What is the difference between a JVM and a JRE?

A JVM (Java Virtual Machine) is an abstract computing machine that enables a computer to run Java programs. A JRE (Java Runtime Environment) is a set of libraries and software tools that are used to run Java programs. It includes a JVM, as well as other class libraries and support files needed to run Java programs.

Difference between Java and C++

Java and C++ are two popular programming languages that have a number of similarities and differences. Here are some key points to consider when comparing Java and C++:

  • Syntax: Java and C++ have similar syntax, as they both use curly braces to define blocks of code and semicolons to end statements. However, Java is generally considered to be simpler and easier to learn than C++, as it has fewer keywords and fewer low-level details to worry about.
  • Object-oriented programming: Both Java and C++ are object-oriented languages, meaning that they support the use of objects and classes to organize and structure code. However, Java is a pure object-oriented language, while C++ is a hybrid object-oriented language that also supports procedural programming.
  • Platform independence: Java is a platform-independent language, meaning that Java code can run on any device that has a Java Virtual Machine (JVM). C++, on the other hand, is not platform-independent, as it is compiled into machine code that is specific to the target platform.
  • Memory management: In Java, memory management is handled automatically by the JVM, using a technique called garbage collection. In C++, memory management is the responsibility of the programmer, and it is typically done using pointers and manual memory allocation/deallocation.
  • Execution speed: C++ is generally considered to be faster than Java, as it is compiled directly into machine code and does not require the overhead of a JVM. However, the difference in execution speed between the two languages can vary depending on the specific code being executed and the hardware it is running on.

What is JRE?

The Java Runtime Environment (JRE) is a standalone runtime environment that is used for running Java applications. It consists of the Java Virtual Machine (JVM) and a set of libraries and other components that are needed to run Java programs.

What is JIT compiler?

The Just-In-Time (JIT) compiler is a component of the Java Runtime Environment (JRE) that improves the performance of Java applications by compiling bytecode into native machine code at runtime.

In the Java programming language, source code is compiled into an intermediate form called bytecode, which is then executed by the JVM. Bytecode is designed to be portable, as it can run on any device that has a JVM, regardless of the underlying hardware and operating system. However, the process of interpreting bytecode can be slower than executing native machine code, which can impact the overall performance of Java applications.

To address this issue, the JIT compiler was introduced as a component of the JRE. The JIT compiler works by compiling bytecode into native machine code on the fly, as the code is being executed. This allows the JVM to skip the interpretation step and execute the code directly, which can significantly improve the performance of Java applications.

The JIT compiler is an optional component of the JRE, and it is typically enabled by default. It can be disabled if desired but doing so may negatively impact the performance of Java applications.

What are the types of memory areas are allocated by JVM

There are several types of memory areas that are allocated by the Java Virtual Machine (JVM) when a Java program is executed. These include:

  • Heap: The heap is a region of memory that is used to store objects and other dynamically allocated data. It is managed by the JVM’s garbage collector, which is responsible for allocating and deallocating memory as needed.
  • Stack: The stack is a region of memory that is used to store local variables, method arguments, and other data that is specific to the current method being executed. Each thread in a Java program has its own stack, and the JVM allocates a fixed amount of memory for each thread’s stack when the thread is created.
  • Method area: The method area is a region of memory that is used to store class and method metadata, such as class and field names, constants, and code for methods and constructors. It is shared by all threads in a Java program, and the JVM allocates a fixed amount of memory for the method area when the program is started.
  • Native method stacks: Native method stacks are used to store data for native methods, which are methods that are written in a language other than Java and are called from a Java program. Like regular stacks, native method stacks are specific to each thread, and the JVM allocates a fixed amount of memory for each thread’s native method stack when the thread is created.
  • PC registers: PC registers are used to store the current program counter (PC) value for each thread in a Java program. The PC register holds the memory address of the instruction being executed by the thread, and it is used to track the progress of the thread as it executes code.

Overall, the JVM allocates these different types of memory areas to support the execution of Java programs and to provide the necessary resources for storing data and executing code.

What is classloader in java with example?

In the Java programming language, a classloader is a class that is responsible for loading Java classes into the Java Virtual Machine (JVM). It is an essential part of the Java runtime environment, as it enables the JVM to locate and load class files as needed.

Here is an example of how a classloader might work in a Java program:

  • A Java program is started, and the JVM creates the bootstrap classloader to load the core Java classes that are part of the Java runtime environment.
  • The program calls a method in a custom class, “MyClass”, which has not yet been loaded into the JVM.
  • The JVM looks for the class file for “MyClass” using the classpath, which is a list of directories and JAR files that the classloader searches when looking for classes.
  • If the class file is found, the JVM uses the application classloader to load the class into memory. The application classloader is responsible for loading classes that are part of the user’s application.
  • The JVM then creates an instance of “MyClass” and calls the requested method.
  • If the class file for “MyClass” is not found, the JVM may throw a “ClassNotFoundException”, indicating that the class could not be located.

This is just one example of how a classloader might work in a Java program. Classloaders can be used to load a wide variety of classes, and they can be customized or extended to support different types of class loading scenarios.

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Java programming language is a powerful and widely used language that is used in a wide variety of applications. In this blog post, we covered the top 15+ Core Java Interview Questions and Answers on Java Basics, which covered a range of topics on Java basics.

We hope that this post has helped you to better understand the basic concepts and features of Java, and that it will be a useful resource as you prepare for technical interviews or continue your journey as a Java developer. Whether you are a beginner or an experienced developer, there is always more to learn and explore in the world of programming, and we encourage you to keep learning and growing as a developer.

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