Each plays a distinct and critical role:
- JDK is the comprehensive toolkit required for developing, compiling, and debugging Java applications.
- JRE provides the necessary environment to run Java programs, bundling the JVM and essential libraries but excluding development tools.
- JVM acts as the engine that interprets and executes compiled Java bytecode, ensuring platform independence and efficient resource management
In Java, the JVM is that universal translator.
The Java Virtual Machine is an abstract engine that reads compiled Java bytecode and executes it on any device, whether it’s a Windows PC, a Mac, or a Linux server.
The JVM is the reason Java is called “write once, run anywhere.” It hides the complexity of hardware and operating systems, letting your code travel the world without change.
- Loads and verifies bytecode
- Converts bytecode to machine code (using interpretation or Just-In-Time compilation)
- Manages memory and garbage collection
- Handles exceptions and threads
Note: The JVM is like a wise chef who can cook any recipe (bytecode) in any kitchen (platform), always delivering the same delicious result.
Imagine walking into a fully equipped kitchen: the pots and pans are ready, all the ingredients are in place, and a skilled chef is on standby. You can not create new recipes here but you can enjoy any dish the chef is already set to cook.
That is exactly what the JRE does for Java applications. It provides everything needed to run Java programs like the Java Virtual Machine (JVM), core libraries, and supporting files. Just like the kitchen is set up for cooking, the JRE is set up for executing Java applications. You can not develop or compile code with it for that, you had need the JDK but you can run any pre-built Java program smoothly.
The Java Runtime Environment is the collection of everything needed to run Java applications: the JVM, core libraries (like java.lang and java.util), and supporting files.
Who needs the JRE?
Anyone who wants to run Java applications, but not develop them. End-users, not developers.
What’s missing?
The JRE does not include the tools to create or compile new Java programs-no compiler, no debugger.
Note: The JRE is the dining room where every Java dish is served-ready to eat, no cooking required.
Now, imagine you are the chef. You do not just need a ready kitchen , you need the full suite of tools: a recipe book for guidance, measuring cups, knives, mixing bowls, and everything required to invent, tweak, and test new dishes.
That is exactly what the JDK is for Java developers. It includes the entire JRE (the runtime environment), but adds essential tools for creating Java programs such as the compiler ( javac), debugger, and other development utilities. The JDK empowers you to write, compile, and build your own Java applications from scratch just like a chef experimenting with new recipes in a fully equipped kitchen.
The Java Development Kit is the complete toolkit for Java creators. It includes the JRE, plus the compiler (javac), documentation generator (javadoc), archiver (jar), debugger, and more.
Who needs the JDK?
Every Java developer-anyone who wants to write, compile, and test Java programs.
Variants:
- Java SE (Standard Edition): For desktop and general-purpose apps
- Java EE (Enterprise Edition): For web and enterprise-level apps
- Java ME (Micro Edition): For mobile and embedded systems
Note: The JDK is the chef’s entire workshop-the only place where new Java recipes are born.
Let’s walk through the life of a Java program:
2. Compilation:
3. Execution:
4. Management:
Difference between the JDK, JRE and JVM
Feature | JDK | JRE | JVM |
---|---|---|---|
Purpose | Develop & Run | Run Only | Execute Bytecode |
Includes | JRE + Dev Tools | JVM + Libraries | Bytecode Engine |
For Developers ? | Yes | No | No |
For End Users ? | Yes | Yes | Indirectly |
Can Compile Code ? | Yes | No | No |
Can Run Code ? | Yes | Yes | Yes ( via JRE/JDK) |
Building Your Java Foundation