java abstract class with generics and inheritance : Bound mismatch

Question

i have 2 abstract classes manipulating generics and 1 factory with generics too. The parent is independent of trips objects and factorize code. The son is based on trips only.

//parent
public abstract class AbstractPurchaseExtractor<//
BINDING_CLASS extends ForPnrHandling, //
PURCHASE extends AbstractServicePurchase<?, PRICING, RECEIPT, ITEM, COUPON>, //
PRICING extends PricingDefault, //
RECEIPT extends ReceiptDefault, //
ITEM extends AbstractServiceItem<PURCHASE, COUPON>, //
COUPON extends CouponDefault> //
    implements IPurchaseExtractor<BINDING_CLASS, PURCHASE, PRICING, RECEIPT, ITEM,     COUPON>
...






//son
public abstract class AbstractTripBasedPurchaseExtractor<//
BINDING_CLASS extends ForPnrHandling, //
TRIP_PURCHASE extends AbstractTripBasedPurchase<?, PRICING, RECEIPT, TRIP_BASED_ITEM,         TRIP_BASED_COUPON> , //
PRICING extends PricingDefault, //
RECEIPT extends ReceiptDefault, //
TRIP_BASED_ITEM extends  AbstractTripBasedItem<TRIP_PURCHASE, TRIP_BASED_COUPON, ?>, //
TRIP_BASED_COUPON extends  TripBasedCouponDefault> //
        extends AbstractPurchaseExtractor<BINDING_CLASS, TRIP_PURCHASE, PRICING,     RECEIPT,     TRIP_BASED_ITEM, TRIP_BASED_COUPON> //
{

@Autowired
private AbstractTripBasedPurchaseFactory<TRIP_PURCHASE, PRICING, RECEIPT, TRIP_BASED_ITEM, TRIP_BASED_COUPON> abstractTripBasedPurchaseFactory;
  ...





//factory
public abstract class AbstractTripBasedPurchaseFactory<PURCHASE extends     AbstractTripBasedPurchase<?, PRICING, RECEIPT, ITEM, COUPON>,
                                                   PRICING extends PricingDefault,
                                                   RECEIPT extends ReceiptDefault,
                                                   ITEM extends AbstractTripBasedItem<?     extends AbstractTripBasedPurchase<?, PRICING, RECEIPT, ITEM, COUPON>, COUPON, ?>,
                                                   COUPON extends     TripBasedCouponDefault>
   extends AbstractPurchaseFactory<PURCHASE, PRICING, RECEIPT, ITEM>
{

i have the error on Eclipse for AbstractTripBasedPurchaseExtractor line 9 : Bound mismatch: The type TRIP_PURCHASE is not a valid substitute for the bounded parameter

<PURCHASE extends AbstractServicePurchase<?,PRICING, RECEIPT, ITEM,COUPON>>

of the type

AbstractPurchaseExtractor<BINDING_CLASS,PURCHASE,PRICING, RECEIPT, ITEM,COUPON>

HERE: extends AbstractPurchaseExtractor '< BINDING_CLASS, TRIP_PURCHASE ...

using extends on the son class, i need to use for TRIP_PURCHASE something that extends AbstractServicePurchase. Actually AbstractTripBasedPurchase extends AbstractServicePurchase. So why the error ?

if i replace AbstractTripBasedPurchase by AbstractServicePurchase as Eclipse is expecting, of course it compiles but i cannot use my trip factory on the son class.

That's too many generic types for me to grok right now, but at first glance, having a wildcard (?) in there is maybe not so great. Does it help if you replace with it with a type placeholder? — Thilo
no, i don't need to replace the wildcard here (?) There is no problem with that. The thing is the extends is expecting me to declare a AbstractServicePurchase class but i pass a son of this class named AbstractTripBasedPurchase. Is weird that is no accepting it, like inheritance is not working — Benjamin Fuentes
can you reduce this to a minimal example that still exhibits the problem? — Thilo
It sounds weird because it compiles with Maven but my java file is red of errors on Eclipse Kepler ... Eclipse bug ??? — Benjamin Fuentes

Benjamin Fuentes Benjamin Fuentes · Accepted Answer · 2014-08-12T13:43:06

The same simplified at maximum.

It works.

public interface IGeneric<OBJECT> {
    public void test(OBJECT o);
}


public abstract class Parent<OBJECT extends AbstractProduct> implements IGeneric<OBJECT> {       
}

public abstract class Son<PRODUCT extends Trip> extends Parent<PRODUCT> {
    IService<PRODUCT> service;   
}

public abstract class AbstractProduct {  
}

public class Trip extends AbstractProduct{ 
}

 public interface IService<TRIP extends Trip> { 
}

java abstract class with generics and inheritance : Bound mismatch

1 Answers