Question

This works:

class ABean implements A {
  protected String field1;
  ...
  protected String fieldn;

  public String getField1() {
   return field1;
  }
  ...
}


class BBean extends ABean {
  public BBean(A a) {
    super();
    this.field1=a.getField1();
    ...
    this.fieldn=a.getFieldn();
  }
}

But writing this constructor B(A a) is cumbersome, not really practical, and error prone because if I add or remove fields in A, then I need to modify that constructor and may sometimes forget to initialize some of the fields present in A.

I suppose I could implement clone for ABean, but that would have similar issues (because the clone implementation would need to be updated when I add/remove fields) and that would also not allow me to have a BBean(A a) constructor; only a BBean(ABean a) constructor unless I make the clone() part of the interface also.

So… is there a cleaner, better way of implementing BBean(A a)?

Answer 1

Instead of using inheritance, try using composition. That is, instead of BBean extends ABean, make your BBean have a constructor BBean(ABean a). That way you’ve shielded yourself from all the details of how to construct a new ABean in BBean‘s code.