> For the complete documentation index, see [llms.txt](https://codewithmeiy.gitbook.io/core-java/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://codewithmeiy.gitbook.io/core-java/overview-of-java/how-a-java-program-runs.md).

# How a Java Program runs?

To run a Java program, you first need to compile it. This converts the Java source code into bytecode, which is a platform-independent format that can be executed by the Java Virtual Machine (JVM).

The JVM is a software program that provides a runtime environment for Java programs. It is responsible for loading and executing bytecode, managing memory, and providing other services that Java programs need.

Once a Java program has been compiled, it can be run by executing the `java` command. This command takes the name of the main class file as an argument. The main class file is the class that contains the `main()` method, which is the entry point for all Java programs.

When the JVM executes a Java program, it first loads the main class file into memory. It then verifies the bytecode to make sure that it is valid. Once the bytecode has been verified, the JVM executes it.

The JVM executes bytecode by interpreting it. This means that it reads the bytecode one instruction at a time and executes it. Modern JVMs also use a technique called just-in-time (JIT) compilation to improve performance. JIT compilation converts bytecode into machine code, which is the native code of the underlying computer architecture.

Java programs run in a sandbox, which means that they are isolated from the underlying operating system. This makes Java programs more secure and reliable.

<figure><img src="https://simplesnippets.tech/wp-content/uploads/2018/03/java-execution-flow-diagram.jpg" alt=""><figcaption><p>Java Program Execution</p></figcaption></figure>

**Here is a summary of the steps involved in running a Java program:**

1. Compile the Java source code into bytecode using the `javac` command.
2. Execute the Java program using the `java` command, passing the name of the main class file as an argument.
3. The JVM loads the main class file into memory and verifies the bytecode.
4. The JVM executes the bytecode, interpreting it or compiling it to machine code using JIT compilation.

Java programs can be run on any platform that has a JVM installed. This makes Java a very portable programming language.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://codewithmeiy.gitbook.io/core-java/overview-of-java/how-a-java-program-runs.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.