> Existing tools can already create, manipulate...

# random

[fellshard]

Existing tools can already create, manipulate, and consume JAR files, so for ease of adoption and migration we define modular JAR files. A modular JAR file is like an ordinary JAR file in all possible ways, except that it also includes a module-info.class file in its root directory. A modular JAR file for the above com.foo.bar module, e.g., might have the content:

```

META-INF/
META-INF/MANIFEST.MF
module-info.class
com/foo/bar/alpha/AlphaFactory.class
com/foo/bar/alpha/Alpha.class
...
```

A modular JAR file can be used as a module, in which case its module-info.class file is taken to contain the module’s declaration. It can, alternatively, be placed on the ordinary class path, in which case its module-info.class file is ignored. Modular JAR files allow the maintainer of a library to ship a single artifact that works both as a module, on Java SE 9 and later, and as a regular JAR file on the class path, on all releases. We expect that implementations of Java SE 9 which include a jar tool will enhance that tool to make it easy to create modular JAR files.