Question

I have class structure like this:

class A1,A2,..,An extends A;
class B1,B2,..,Bn extends B;

And class that converts Ai into Bi:

    private B1 convert(A1 a1){}
...
    private Bn convert(An an){}

How can I define single public method with signature like <? extends B> convert(<? extends A> a)?
Now I have only this approach:

    B convert(A a){
      if(A.getClass().equals(A1.class)){
         return convert((A1)a);
      }...
    }

Can I use instanceof if perfomance is important and the method will be called frequently?

Answer 1

A more elegant solution will probably be to declare a method in A: [preferably abstract, if A is abstract]:

public abstract B toB();

Overriding classes (A1,A2,…) will have to override it and instantiate their own B object.

Code snap [the static modifier is used since I implemented it as an inner class, it is not needed and cannot be used if the classes are outer classes]:

public abstract static class A { 
    public abstract B toB();
}
public static class A1 extends A {
    @Override
    public B1 toB() {
        return new B1();
    } 

}

public static class B {

}
public static class B1 extends B { 

}