Creating a class to extend for an API

Question

I am trying to create an API in java for my Uni project.

Is the following possible.

I have 2 versions of MyClass where one does not contain code in the method bodies.

for example:

Full Version:

public MyClass {
     public String name;

     public MyClass(String name) {
          this.name = name;
     }

     public String getSpecialVersion(){
         return name + name;
     }
}

API Version:

public MyClass {
     public String name;

     public MyClass(String name) {}

     public String getSpecialVersion(){ return null; }
}

The idea being a user extends the API version of the class, but the full version of the class is loaded at runtime.

Is this possible in Java, or is there a better way to do it?

Thanks in advance!

Answer 1

You want to create an interface and let the "with code"-version implement that interface.

public interface IMyClass {

    public String getSpecialVersion();

}

Implementation:

public class MyClass implements IMyClass {

    public String name;

    public MyClass(String name) {
         this.name = name;
    }

    @Override
    public String getSpecialVersion() {
        return name + name;
    }

}

You cannot define constructors in interfaces (and defining fields in interfaces is kind of unconventional) tho, so you might want to look at abstract classes for that, too:

public abstract class AbstractMyClass {

    public String name;

    public AbstractMyClass(String name) {
         this.name = name;
    }

    public abstract String getSpecialVersion();

}

This class can be extended by a concrete class to add the method body:

public class MyClass extends AbstractMyClass {

    public MyClass(String name) {
        super(name);
    }

    @Override
    public String getSpecialVersion() {
        return name + name;
    }

}