Tutorial 2 - Creating a Composite

In this tutorial we will create a TransientComposite interface that ties all pieces together. The TransientComposite interface is a regular Java interface which extends the interfaces you want to expose from your domain model, and which uses various annotations to declare what Fragments to include. Fragments include Mixins, Concerns, SideEffects and Constraints. In this tutorial we will only use Mixins. When a TransientComposite is instantiated at runtime the framework will inspect the interface to determine what the TransientComposite instance should look like in terms of used Fragments.

In Qi4j all method parameters are considered mandatory unless marked as @Optional. Therefore you can remove the null checks in the Mixin. If a null value is passed in an exception will be thrown by Qi4j.

Steps for this tutorial:

1. Create an interface that extends the domain interface HelloWorld and org.qi4j.api.composite.TransientComposite.
2. Add a @Mixins annotation to it with the name of the Mixin as argument.

Solution

If you have successfully completed the task, you should end up with the following artifacts;

HelloWorld.java
HelloWorldBehaviour.java
HelloWorldComposite.java
HelloWorldMixin.java
HelloWorldState.java