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JDK vs. JVM vs. JRE in Java – Understanding the Core Components

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Dennis Temoye
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4 min read

Java powers billions of devices worldwide, from enterprise servers to Android apps. Its "Write Once, Run Anywhere" capability makes it one of the most versatile programming languages. But what enables Java to achieve this remarkable portability?

At the heart of Java’s execution process are three fundamental components, JDK (Java Development Kit), JVM (Java Virtual Machine), and JRE (Java Runtime Environment).

If you’re new to Java, understanding these three components will help you grasp how Java programs are written, compiled, and executed. Let’s break them down.

What is the JDK (Java Development Kit)?

The Java Development Kit (JDK) is the essential toolkit for Java developers. It provides everything needed to write, compile, and debug Java applications.

It includes the compiler (javac) to convert Java code into bytecode, the Java Virtual Machine (JVM) to execute the bytecode, and the Java Runtime Environment (JRE), which provides the necessary libraries for running applications. Additionally, it comes with various development tools like debuggers and performance analyzers to aid in efficient coding and debugging.

How the JDK Works

The JDK follows a step-by-step process to transform Java code into a running application:

  1. Writing Code: A Java program is written and saved as a .java file.

  2. Compiling Code: The JDK’s compiler (javac) converts the code into bytecode (.class file).

  3. Executing Code: The JVM reads the bytecode and runs the program inside the JRE.

If you're developing Java applications, the JDK is essential as it provides the tools needed to write, compile, and execute Java code.

What is the JVM (Java Virtual Machine)?

The Java Virtual Machine (JVM) is a virtual machine that interprets or compiles Java bytecode into a machine. It allows Java applications to be executed on different operating systems without modification.

How the JVM Works

  1. The JVM loads Java bytecode into memory.

  2. It converts bytecode into native machine code using Just-In-Time(JIT) complication

  3. The program runs in the system, regardless of the operation system.

Think of the JVM as a movie projector that plays a film (Java bytecode) on any screen without needing modifications.

Every Java application runs inside a JVM instance, making Java platform-independent.

What is the JRE (Java Runtime Environment)?

The Java Runtime Environment (JRE) provides the necessary resources to execute Java applications. It includes:

  • JVM: The core engine that runs Java programs.

  • Core Java Libraries: It includes essential classes for input/output, networking, and data structures.

  • Runtime Configuration Files: It provides settings and system properties needed for execution.

How the JRE Works

  1. The JRE provides the necessary libraries for Java programs.

  2. The JVM runs the compiled bytecode using these resources.

  3. The program executes successfully on the system.

For Instance, If the JDK is the workshop, and the JRE is the power supply, it provides the necessary resources to run the tools and complete the job.

If you're only running Java applications (not developing them), you only need the JRE, not the JDK.

Now, let’s look into how JDK, JVM, and JRE Work Together.

How JDK, JVM, and JRE Work Together

Understanding how JDK, JVM, and JRE interact is fundamental to mastering Java development. Each component plays a distinct role in the process of writing, compiling, and executing Java applications.

Here’s a structured breakdown of how they work together:

  1. Writing Java Code: A developer writes Java source code and saves it as a .java file using the JDK.

  2. Compiling the Code: The JDK compiles the .java file into bytecode (.class), making it ready for execution.

  3. Running the Program: The JVM interprets the bytecode and executes it within the JRE, ensuring platform independence.

Importance of JDK, JVM, and JRE

Understanding how JDK, JVM, and JRE work together is crucial for every Java developer. These components form the backbone of Java’s execution process and contribute to its platform independence.

  • JDK is essential for writing and compiling Java programs.

  • JVM enables Java’s “Write Once, Run Anywhere” principle.

  • JRE provides the runtime environment needed to execute Java applications.

  • Java’s cross-platform compatibility is powered by the JVM, making it one of the most widely adopted programming languages.

Mastering these components will help you write, compile, and execute Java programs more effectively.

Conclusion

In this article, we explored JDK, JVM, and JRE and how they work together to make Java platform-independent. The JDK is used for writing and compiling Java code, the JVM executes the compiled bytecode, and the JRE provides the necessary environment to run Java applications. Understanding these components is essential for building and running Java programs efficiently.

Happy Coding!

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