Struggling with Java Generics

The idea of Java generics looks straightforward. Really, templates exist in C++ for years, and one doesn't expect too much trouble with much simpler syntax of Java generics. But devil is in details. The major caveat is verifiability requirement.

Look at this [oversimplified] C++ design:

// Class that creates copies of objects of

// given typename T

template<typename T>

class Copier {

private:

    T* t;

public:

    Copier() : t(NULL) {}

   

    T* getCopy() {

        if(t == NULL) {

            t = new T();

        }

        return t->createCopy();

    }

};

   

// Class that is capable to create

// copies of objects of more than one type;

// it uses Copier as a building block

template<typename A, typename B>

class CopyMaster {

private:

    Copier<A> copierA;

    Copier<B> copierB;

public:

    A* getA() {

        return copierA.getCopy();

    }

    B* getB() {

        return copierB.getCopy();

    }

};

   

// Two concrete classes Dolly and Lizard

// can create copies of themselves and are

// ready to be used in Copier<>

class Dolly {

public:

    Dolly* createCopy() {

        return new Dolly();

    }

};

   

class Lizard {

public:

    Lizard* createCopy() {

        return new Lizard();

    }

};

   

   

int main(int argc, char* argv[]) {

    // This particular instance of CopyMaster

    // can create copies of sheep and reptiles

    CopyMaster<Dolly, Lizard> copyMaster;

    Dolly* concrete1 = copyMaster.getA();

    Lizard* concrete2 = copyMaster.getB();

    return 0;

}

The challenge is to achieve the same functionality with Java generics.