Question

This is bad programming practice but I’ve been asked to do it as part of a larger assignment.

I am creating a superclass and then 2 subclasses. There is a static method in the superclass that should return either of the 2 subclasses depending on the result. How would I go about writing this method?

For example I need to do something like this

public abstract class Superclass{
    public static subclass? createFromFilename(String fileName){
            if(1==1)
               return subclass1;
            else
                   return subclass2;
    }
}

Is this even possible?

Answer 1

You can do it like this

public abstract superClass
{
     public static superClass getBaseClass(...)
     {
           if(...)
           {
                 return new baseClass1();//baseClass1 should derive from superClass
           }
           else
           {
                 return new baseClass2();//baseClass2 should derive from superClass
           }
     }
}

You can now do this

superClass sc=superClass.getBaseClass(..);

if(sc instanceof baseClass1)
{
     baseClass1 bc1=(baseClass1)sc;
     //work with bc1...
}

if(sc instanceof baseClass2)
{
     baseClass2 bc2=(baseClass2)sc;
     //work with bc2...
}