Scala Cake Pattern Simplified for Java

[William la Forge]

The Scala Cake pattern is important for Rolonic Software Engineering, as it can be used to implement the elements of a Rolon. But it doesn't really need multiple inheritance to implement. It is really just a invariant of aggregation which makes use of uninitialized constants--which Java also supports. Here's how to implement a 3-layer cake using Java:

public class Component {

  public final A a;

  public final B b;

  public final C c;

  //_configure can only be executed once without raising an exception

  protected void _configure(A a, B b, C c) {

    this.a = a; this.b=b; this.c=c; 

  }

  public void configure(A a, B b, C c) {

    if (this instanceof A) {

      a = this;

    } else if (a==null) {

      a = new A();

    }

    if (this instanceof B) {

      b = this;

    } else if (b==null) {

      b = new B();

    }

    if (this instanceof C) {

      c = this;

    } else if (c==null) {

      c = new C();

    }

    a._configure(a,b,c);

    b._configure(a,b,c);

    c._configure(a,b,c);

  }

}

public class A extends Component {

  protected String fun;

  public String getFun() {return fun;}

  public void setFun(String fun) {this.fun = fun;}

}

public class B extends Component {

  public String games() {return a.fun()+" World!"}

}

public class C extends Component {

}

//sample code

C s = new C();

s.configure(null,null,null);

s.a.setFun("Hello");

System.out.println(s.b.games());