Question

I have a rather basic question about interfaces, something I’m rather new too. I typically would instantiate my class with an overloaded constructor. I’m now trying to use interfaces and wondering how I would populate my constructor. Would I just use something like setSomeMethod(arguement1, arguement2) in my interface to populate my attributes?

I’d also like to note I’m using “Tapestry5” framework with service Injection. Example

public class Main {

    @Inject
    private Bicycle bicycle;

    public Main() {
         //Not sure how to pass constructor variables in
         this.bicycle();
    }

}

Interface

public interface bicycle {
   public void someMethod(String arg1, String arg2);
}

Impl Class

public class MountainBike implements bicycle {

   private String arg1;

   private String arg2;

   public MountainBike() {
       //Assuming there is no way to overload this constructor
   }

   public void someMethod(String arg1, String2 arg2) {
       this.arg1 = arg1;
       this.arg2 = arg2;
   }

} 

Then how do you handle extended classes? I’m not sure how to populate the extended class constructor.

public class MountainBike extends BicycleParts implements bicycle {

   private String arg1;

   private String arg2;

   public MountainBike() {
       //Assuming there is no way to overload this constructor
       //Not sure where to put super either, but clearly won't work here. 
       //super(arg1);            
   }

   public void someMethod(String arg1, String2 arg2) {
       this.arg1 = arg1;
       this.arg2 = arg2;
       //Assuming it doesn't work outside of a constructor, so shouldn't work 
       //here either.   
       //super(arg1);
   }

} 

public class BicycleParts {

    private String arg1;

    public void BicycleParts(String arg1) {
        this.arg1 = arg1;
    }

}

Thanks in advance.

Answer 1

First off, your bicycle method should be declared with a return type:

public void someMethod(String arg1, String arg2);

Interfaces define a contract for methods and not how objects are instantiated. They can also define static variables.

To use someMethod in your MountainBike constructor, you could make the call in the constructor:

public MountainBike(String arg1, String arg2) {
   someMethod(arg1, arg2);
}

Wrt, your question on extending the class, the super statement must appear as the very first statement in the constructor i.e.:

public class MegaMountainBike extends BicycleParts implements bicycle {

   public MegaMountainBike() {

      super("Comfy Saddle");
      // do other stuff
   }