Question

I have an interface hierarchy similar to –

interface Type
{
    Type copy();
};

interface SubType extends Type
{
};

interface SubSubType extends SubType
{
};

And a concrete class

public class Concrete implements SubSubType
{
    @Override public Concrete copy() { return new Concrete(); }
}

I would like to be able to call copy() on a Type and get a Type back, call copy() on a SubType and get a SubType back, etc. Is this achievable? Possibly with generics?

Thanks in advance.

Answer 1

Like so:

public interface Type { 
  public Type copy();
}

public interface SubType extends Type { 
  public SubType copy();
}

public class Concrete implements Type { 
  @Override
  public Concrete copy() {
    return new Concrete();
  }
}

public class SubConcrete implements SubType {
  @Override
  public SubConcrete copy() {
    return new SubConcrete();
  }
}

public static void main(String[] args) {
  Type    type    = new Concrete();
  SubType subType = new SubConcrete();

  Type    newType    = type.copy();
  SubType newSubType = subType.copy();
}