Difference Between JDK, JRE, and JVM

Java has stood the test of time and has emerged as one of the most popular programming languages since its inception in 1996. A big part of the reason for its success is that it follows the “Write Once, Run Anywhere” philosophy. This means that a single code base can be used to run applications on multiple platforms, including Windows, macOS, Linux, etc. This is made possible thanks to the three core components of the Java ecosystem, namely, the Java Development Kit (JDK), Java Runtime Environment (JRE), and Java Virtual Machine (JVM). 

Today, we will explore how these 3 components work together to build and run a Java application. Let’s get started.

Table of Contents:

• Introduction to JDK, JRE, and JVM in Java
• Difference Between JDK, JRE, and JVM
• What is the Java Virtual Machine (JVM)?
• What is the Java Runtime Environment (JRE)?
• What is the Java Development Kit (JDK)?
• How JDK, JVM, and JRE in Java Work Together
• Choosing Between Java JDK vs. JRE
• Common Errors and Debugging Tips in the Java Environment
• Conclusion

Introduction to JDK, JRE, and JVM in Java

The JDK, JRE, and JVM form the backbone of the Java platform and play a role in everything from writing and compiling code to executing and managing it efficiently across different environments. 

 Each of them plays a specific role:

• JDK helps you build Java apps.
• JRE lets you run them.
• JVM makes sure the code executes on your machine, enabling platform independence by providing OS-specific implementations. 

Difference Between JDK, JRE, and JVM 

While JDK, JRE, and JVM in Java are closely related and often used together, they serve distinct purposes in the Java ecosystem. Understanding the capabilities and limitations of each will help you build more robust and scalable Java applications.

Here is a simple breakdown of how JVM, JRE, and JDK in Java differ from each other. Think of it like a relay race:

• The JDK is a complete toolkit used to build Java applications.
• The JRE provides the environment required to run those applications.
• The JVM is the one that actually executes the bytecode generated from the Java source code.

Comparison Table: JDK vs JRE vs JVM

Now let’s dig under the hood and learn in detail how each one fulfils its specific functions.

What is the Java Virtual Machine (JVM)?

During the compilation of a Java program using the JDK, the Java code is converted into an intermediate form known as bytecode instead of machine code. The JVM handles this bytecode instead of the operating system; each operating system has its own implementation of the JVM. This abstraction allows for the same code base to be used for multiple platforms. 

In essence:

Key Components of JVM Explained

Now that we have an understanding of what the JVM does, let’s dig a little deeper into how it is able to do it and what happens under the hood.

1. JVM Class Loader Subsystem

The Class Loader is a component of the JVM that is responsible for loading class files at runtime. It follows a three-phase process, namely, Loading, Linking, and Initialization. Classes are only loaded when needed (lazy loading), which improves performance. 

2. Runtime Data Areas in JVM

When a Java program runs, the JVM sets up different memory areas to handle everything from loading classes to storing objects and executing methods. Some of these areas are shared across threads, while others are private to each thread. Here’s a quick breakdown of what each one does:

• Method Area: It stores class-level structures such as metadata, static variables, method data, and the runtime constant pool. It is a shared memory area and is created when the JVM starts, and is common to all threads.
• Heap: It is used to store all Java objects and class instances. This area is also shared among threads and is the largest memory area. It is the primary target for Garbage Collection(GC).
• Stack: Each thread gets its own JVM stack, which stores frames. A frame holds local variables, operand stacks, and method call information. When a method is invoked, a new frame is created on the stack.
• Program Counter (PC) Register: A small memory space that stores the address of the currently executing instruction for each thread. It helps the JVM resume the thread’s execution properly after context switching.
• Native Method Stack: Used to support native (non-Java) method calls written in languages like C or C++. It stores native method information and is separate from the JVM stack used for Java methods.

3. JVM Execution Engine: Interpreter & JIT Compiler

Once your Java code is compiled into bytecode, the JVM’s Execution Engine takes over and makes it run. It does this with the help of two key components:

• Interpreter: Executes bytecode instructions line by line.
• JIT Compiler (Just-In-Time): Converts frequently executed bytecode into native machine code for better performance.

What is Just-In-Time (JIT) Compilation in JVM?

The Just-In-Time(JIT) compiler speeds up the execution process by compiling bytecode into native machine code and caching it. This way, frequently used code doesn’t need to be interpreted over and over again, increasing performance drastically.

How JVM Handles Garbage Collection in Java

Memory management is an integral part of the performance of any application. Java uses Garbage collection, which is an automatic memory management process that identifies and removes unused objects from the heap to free up memory and prevent leaks.

The JVM uses various GC algorithms, like:

• Serial GC
• Parallel GC
• G1 (Garbage First) GC
• ZGC

Garbage Collection in Java is done automatically, but you can optimize it based on your application’s needs by configuring JVM flags.

What is the Java Runtime Environment (JRE)?

The Java Runtime Environment (JRE) is what you need if you only want to run Java Applications and not write them. It’s a package that includes:

• The JVM (for running the code)
• Core class libraries (like java.util, java.io, etc.)
• Supporting files and config settings

In other words, if the JVM is the engine, the JRE is the full vehicle.

JRE’s Role in Running Java Programs

When you execute Java code from the terminal or open a .jar file, the JRE is what works in the background to make sure everything runs smoothly.

Here’s how it works:

• The JVM, which is part of the JRE, reads and executes the Java bytecode.
• The Java libraries (like java.util, java.io, etc.) provide all the built-in features your program needs, like reading files, managing data, or working with the network.
• Everything runs on your operating system as if the app were built just for it.

What is the Java Development Kit (JDK)?

So far, we have covered how Java code is executed and how Java applications are made to run on your machine. Now, let’s move on to the component that facilitates the development of Java applications, which is the Java Development Kit (JDK). The difference between the JDK and JRE is that the JDK is a superset of the JRE. This means that the JDK includes everything in the Java Runtime Environment, along with additional development tools. The JDK basically turns your machine into a full-fledged Java development environment, giving you everything needed to develop and package Java applications into runnable .jar files.

Why Developers Need the JDK

Think of the JDK as a Java developer’s toolbox that contains everything you need to turn your ideas into real-world applications. It is what allows you to:

• Write Java code using your favorite IDE or a text editor
• Compile .java source files into .class bytecode
• Debug and monitor applications during development
• Use annotation processors, documentation tools, and packaging utilities

Key Tools and Components of JDK

Here are the main tools included in the JDK:

How JDK, JVM, and JRE in Java Work Together

Think of the relationship between JDK, JRE, and JVM as:

1. You write code with the JDK
2. You run the code with the JRE
3. The code is executed by the JVM

This interdependency ensures a smooth transition from development to execution across platforms. 

Choosing Between Java JDK vs. JRE

When you are just starting out with Java application development, the choice between the JDK and the JRE can be a difficult one to make. Let’s explore some real-world use cases so that you have all the information that you need to make the right decision.

When to Install JDK vs. JRE

JDK includes JRE by default starting from Java 9. So, installing the JDK covers all your needs. But be sure to use JRE for instances when you only need to run applications and not write any code, as it is more lightweight.

When to Use JRE Instead of JDK

You can make do with just the JRE if:

• You’re not writing or compiling Java code.
• You’re deploying a Java application in production.
• You’re using Java-based tools or platforms (e.g., Apache Tomcat, Minecraft mods) that require Java to run but not to develop.

How to Check Java Version

If you want to know which version is currently running on your machine, you can use the following code commands in your terminal.

java -version

To check if the compiler (javac) is available (i.e., JDK is installed):

javac -version

If these commands fail, it usually means Java isn’t installed properly or the PATH variable isn’t set.

Common Errors and Debugging Tips in the Java Environment

Even seasoned Java developers come across common issues when setting up or running Java applications. Knowing how to identify and fix these problems can save valuable time during development. Here are some of the most commonly faced issues and errors for JVM, JDK, and JRE in Java.

Fixing the “Java is Not Recognized” Error

Error:

‘java’ is not recognized as an internal or external command, operable program or batch file.

Cause:

This usually means Java is not added to the system’s environment variables (PATH).

Solution:

• Locate your Java installation directory (e.g., C:\Program Files\Java\jdk-17\bin)
• Add the bin folder path to your system’s PATH variable.
• Restart your terminal or IDE.

Mismatch Between JDK and JVM Versions

Scenario:

Code is compiled using one JDK version (e.g., Java 17), but the system is running a lower JVM version (e.g., Java 11).

Error Example:

Unsupported major.minor version 61.0

Solution:

• Ensure both compile-time and runtime environments match.
• Use javac -target and -source options for backward compatibility:

javac -source 11 -target 11 HelloWorld.java

Conclusion

Understanding the differences between the JDK, JRE, and JVM is essential for anyone serious about learning or working with Java. Each plays a distinct role in the Java ecosystem—whether you’re writing code, compiling it, or simply running a Java application. Understanding when and how to use each component ensures smoother development and deployment.

If you’re ready to dive deeper into Java development, we recommend exploring our free Java certification course. It’s packed with beginner-to-intermediate concepts designed to help you start building real-world Java applications right away.

Difference Between JDK, JRE, and JVM – FAQs