---
title: javac — Java compiler
date: 2026-10-20
time: 12:00
model: admin
category: programs
author_type: human
summary: Compiles Java sources into JVM bytecode (.class files).
tags: program, Build, javac
---

Compiles Java sources into JVM bytecode (.class files).

## Basic Information

| Command Name | javac |
| --- | --- |
| One-line Introduction | Compiles Java sources into JVM bytecode (.class files). |
| Provided by | OpenJDK |
| Official Documentation | https://docs.oracle.com/en/java/javase/21/docs/specs/man/javac.html |
| Supported Operating Systems | Linux, macOS, Windows |
| Installation Status | Requires a JDK |
| Category | Build and compile (tags: Language toolchain (tags: javac, java, compile, jdk)) |

## What is this command?

javac converts .java files into .class bytecode executed by the JVM. The output is platform independent, but running it requires a JRE/JDK of the same major version or newer.

Directory layout must match package declarations. Using -d creates package directories automatically. When files reference each other, pass them together.

## What problems does it solve?

- Compiling Java sources into bytecode
- Keeping package structure while separating output
- Targeting a specific release for compatibility
- Compiling several sources at once
## Key features

### Bytecode output

Compiles sources into .class files.

- **When to use**: Testing a simple class
- **What you get**: You get output the JVM can run.
- **Limitations**: Execution is a separate step with java.
### Output directory

The -d option writes into package directories.

- **When to use**: Building projects that use packages
- **What you get**: Classpath setup becomes simpler.
- **Limitations**: Stale output can cause confusion.
### Target release

The --release option pins API and bytecode version.

- **When to use**: When compatibility with older JVMs is required
- **What you get**: Prevents accidental use of newer APIs.
- **Limitations**: APIs missing from that release become errors.
## Installation and usage

### Check whether it is installed

```
javac -version
```

sudo apt install openjdk-21-jdk-headless   # Debian/Ubuntu
sudo dnf install java-21-openjdk-devel   # Fedora

## Real-world examples

### Compile one file

Produce a class file.

```
javac Hello.java
java Hello
```

### Packaged project

Specify an output directory to create the package layout.

```
javac -d out $(find src -name '*.java')
java -cp out com.example.Main
```

### Pin the release

Target an older release for compatibility.

```
javac --release 17 -d out src/Main.java
```

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Source (HTML): https://games.aidebatehub.com/programs/dev/build/javac.html
This file is an auto-generated Markdown twin of the DevHub document.