Interface as an method/constructor parameter

Question

I am trying to use an existing package to create my own app upon it. However I do not know how to call an interface parametrized method.

On the package there is a class that's constructor is

public class App{
protected App(Logic logic) {
 this(logic.configuration().welcomeScreen, logic.configuration().appName, Optional.of(logic));
}
}

And the interface is this:

public interface Logic extends X, Y {
default Configuration configuration() {
 return new AppConfiguration(1000, "Hello world", true);
}
default void initialize() {
 System.out.println("Starting the application.");
}
}

And Configuration goes like this:

public final class Configuration {
public final int tick;
public final String appName;
public final boolean welcomeScreen;
public Configuration(int tick, String appName, boolean welcomeScreen) {
 this.tick = tick;
 this.appName = appName;
 this.welcomeScreen = welcomeScreen;
}
}

How do I call the App with the configurations that aren't default (1000, "Hello world", true)?

The question is similar to this: interface as a method parameter in Java but I can't grasp on the idea of having interface as parameter.

Answer 1

You provide a class that implements the interface and override those methods; as simple as that. default methods are overridable and your method that takes this interface as parameter can take that new class as parameter (since it implements the interface); and thus methods from the class will be called.

• Hjell: There comes an error that I cannot override the method. That is since there is no public-notation on the configuration() method. Can I access the App(Logic logic) somehow through the AppConfiguration-method which is public?
• Eugene: @Hjell no idea how that would not be possible. For example: interface Test { default String getIt() { return ""; } } class Impl implements Test { @Override public String getIt() { return ""; } }
• Hjell: My bad, the errror was setting it public. (No idea why it did not compile correctly without it). Now do I just set the example of Impl as parameter?
• Eugene: @Hjell if that helped you could accept the answer
• Hjell: It helped but did not solve my problem. Now when I overrride it doesn't recognize it for some reason. Code is as follows: public class Z implements Logic{ @Override public Configuration configuration(){return new Configuration(10,"Test",false);} public static void main(String[] args){launch(args)}} Still it uses the same values as default configuration().Is there a reason why that doesn't work?