如何将 .class 文件加载到变量中？

Question

I'm working on a text-based game as a practice project.

I already managed to write an engine that displays information and handles user input. It draws the games content from custom Scene classes. More precisely, I have a Scene superclass and create child-classes, like EvilDungeon extends Scene , for the actual playable levels.

All scenes are located in a "Scenes"-folder, but I want to be able to make game expansions later on by dropping additional.class files of new scenes into said folder.

My plan was to use loadClass when the game is started to add them to a Scene -array, but it requires the class names which I can't know, since there can a any random combination of scenes in the Scenes-folder.

How can I load all scenes in the folder without knowing which scenes exactly are present? Can I retrieve the class name somehow?

Answer 1

My plan was to use loadClass when the game is started to add them to a Scene-array, but it requires the class names which I can't know, since there can a any random combination of scenes in the Scenes-folder.

That's what Service Provider Interfaces are for. Just define an interface for your plugins and use ServiceLoader to get an instance of each plug-in.

The plug-in needs to provide a text-file in /META-INF/services named after the interface and containing the class which implements that interface (both names must be fully qualified). You'll find the details in the documentation of ServiceLoader .

This gives you the ability to add plugins to the class-path. Eg you can run your application using something like java -cp myapp.jar;plugins/* my.app.Main , then all the plugin-Jars in folder plugin will be added to the class-path and are available to your application (for more information on the asterisk, see this answer ).

If you want to load plug-ins at runtime, you can use a URLClassLoader, eg read this question or thistutorial on how to use the URLClassLoader.