Diamond operator extends one or another

Question

In my code I have two classes that are very similar (but still different), yet I want to map them both to a third class. I have it this way:

class AToCMapper {

    public C from(A a) {
        // My mapping code
    }
}

class BToCMapper {

    public C from(B b) {
        // Same mapping code
    }
}

A and B are slightly different, but the code to map to C is identical. To avoid duplication I would like to have something like this:

class CMapper {

    public <T extends A | B> from (T t) {
        // My mapping code
    }
}

Is there a way to do so? Or am I stuck with duplicated code?

Answer 1

Try defining a MappableToC interface that both A and B implement.

For example:

interface MappableToC {
  String getLabel();
  Number getData();
}

class A implements MappableToC {
  String name;
  int value;

  public String getLabel() {
    return name;
  }

  public Number getData() {
    return value;
  }
}

class B implements MappableToC {
  String title;
  double amount;

  public String getLabel() {
    return title;
  }

  public Number getData() {
    return amount;
  }
}

class C {
  String label;
  Number data;
}

class CMapper {
  public C map(MappableToC source) {
    C target = new C();
    target.label = source.getLabel();
    target.data = source.getData();
    return target;
  }
}

public class Main {
  public static void main(String[] args) {
    CMapper mapper = new CMapper();

    A aInstance = new A();
    aInstance.name = "Example A";
    aInstance.value = 42;
    C cFromA = mapper.map(aInstance);
    System.out.println(cFromA.label);
    System.out.println(cFromA.data);

    B bInstance = new B();
    bInstance.title = "Sample B";
    bInstance.amount = 3.14;
    C cFromB = mapper.map(bInstance);
    System.out.println(cFromB.label);
    System.out.println(cFromB.data);
  }
}

Output:

Example A
42
Sample B
3.14

Try on godbolt.org