通用接口实现不起作用

Question

My interface is:

public interface SalesForceRecordService<T extends SalesForceRecord> {

    T update(T record) throws IOException;
}

My implimentation class is:

public class SalesForceRecordServiceImpl<T extends SalesforceRecordImpl> implements SalesforceRecordService {

  @Override
    public T update(T record) throws IOException {
        return null;
    }

}

@Override gives error, method does not override method from its superclass.

I can't able to understand what is the problem.

Answer 1

You have to pass a type to the super class because it expects one. If you want your SalesForceRecordServiceImpl to also be generic like you posted, then pass the T to SalesForceRecordService .

Try this:

public class SalesForceRecordServiceImpl<T extends SalesForceRecordImpl>
        implements SalesForceRecordService<T> {

    @Override
    public T update(T record) throws IOException {
        return null;
    }
}

Also judging by its name SalesForceRecordImpl looks to me like a concrete implementation, so maybe you just want this:

public class SalesForceRecordServiceImpl
        implements SalesForceRecordService<SalesForceRecordImpl> {

    @Override
    public SalesForceRecordImpl update(SalesForceRecordImpl record)
            throws IOException {

        return null;
    }
}

Answer 2

Firstly on the implementing class, you should also pass the type template into the interface description. Otherwise the compiler has no way of checking the T supplied on SalesForceRecordServiceImpl is compatible with that of SalesforceRecordService

public class SalesForceRecordServiceImpl<T extends SalesforceRecordImpl> 
  implements SalesforceRecordService<T> {
   ...

(I'm assuming SalesforceRecordImpl is a subtype of SalesforceRecord)

Secondly, forcing method to implement an interface using @Overrides annotation only available from java 6 onwards, so if you're on java 5 you'll get a compiler error