What is JVM, JDK, and JRE?Explained in Simple Words (Notes)

Ramesh Fadatare

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Mar 21, 2025

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Java has a powerful architecture that makes it platform-independent, secure, and robust. But to truly understand how Java works, you need to know the difference between:

• 🔥 JVM (Java Virtual Machine)
• 📦 JRE (Java Runtime Environment)
• 🛠️ JDK (Java Development Kit)

1️⃣ JVM (Java Virtual Machine)

🧠 JVM is the brain behind Java.

What it does:

• It runs Java bytecode (compiled .class files).
• Converts bytecode into machine-specific instructions.
• Provides features like: Garbage collection, Memory management, Security and runtime optimization.

Analogy:

Think of JVM as a translator who reads your bytecode and speaks to your operating system in its own language (machine code).

Important:

Every OS (Windows, macOS, Linux) has its own version of JVM.

2️⃣ JRE (Java Runtime Environment)

⚙️ JRE is a software package that contains everything needed to run a Java program.

What it includes:

• JVM (Java Virtual Machine)
• Libraries and class files needed at runtime (like rt.jar)
• Other supporting files

What it doesn’t include:

• Compiler (javac)
• Development tools

✅ Use JRE when you want to RUN Java programs only (not develop them).

3️⃣ JDK (Java Development Kit)

🧑‍💻 JDK is the full toolbox for Java developers.

What it includes:

• JRE (which includes JVM)
• Java compiler (javac)
• Debugger (jdb)
• Other dev tools (like jar, javadoc, etc.)

✅ Use JDK when you want to WRITE, COMPILE, and RUN Java programs.

Popular JDKs:

• Oracle JDK
• OpenJDK
• Amazon Corretto
• Eclipse Temurin

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