Adding Behaviour

In previous articles we created a simple helloworld application without any hand written code. This article shows how to add some hand written business logic.



Alternative video format (mpg)

The behaviour to implement is that the Planet should be able to construct a greeting message based on its population. Test for this behaviour looks like this:

public class PlanetTest {

  @Test
  public void shouldSayHelloWhenHasPopulation() {
      Planet earth = new Planet("Earth");
      earth.setPopulation(7000000000L);
      String message = earth.greeting();
      assertEquals("Hello from Earth", message);
  }

  @Test
  public void shouldBeQuietWhenNoPopulation() {
      Planet pluto = new Planet("Pluto");
      String message = pluto.greeting();
      assertEquals("", message);
  }
}

The video illustrates how to implement this.

As you see nothing special, you add the business logic in Java as usual.

Separation of generated and manually written code is done by a generated base class and manually written subclass, a gap class. It is in the subclass you add methods to implement the behavior of the Domain Object. The subclass is also generated, but only once, it will never be overwritten by the generator.

The gap class is not generated initially. When you need a gap class you specify that in the DSL with gap keyword.