Generics compilation error

Question

Error appears in android project using ormlite I get compilation error on this code:

public class DatabaseModel {
        private Dao<Object, Integer> mDao = null;
        private DatabaseHelper mHelper;
        private Class<?> mClass;

        public DatabaseModel(DatabaseHelper h, Class<?> c) {
                mHelper = h;
                mClass = c;
                try {
                        mDao = mHelper.getDao(mClass);
                } catch (SQLException e) {
                        Debug.e("Can't get dao", e.getStackTrace());
                        throw new RuntimeException(e);
                }
        }

on line 25 mDao = mHelper.getDao(mClass);

Error: type parameters of <D>D cannot be determined; no unique maximal
instance exists for type variable D with upper bounds
     com.j256.ormlite.dao.Dao<java.lang.Object,java.lang.Integer>,
     com.j256.ormlite.dao.Dao<capture#296 of ?,?>

But when i tries to build project using eclipse it works fine

The error looks similar to this SO question.

I don't know whether this bug of Idea or javac.

My configuration: IntelliJ IDEA 11.0.2 Build #IC-111.277 Built on 1 Февраль 2012 г. JDK: 1.6.0_29 VM: Java HotSpot(TM) 64-Bit Server VM Vendor: Apple Inc.

I'd like to have a look at the `DatabaseHelper.getDao()` method. — Malcolm, Feb 23 '12 at 10:36

score 1 · Accepted Answer · answered Feb 23 '12 at 14:43

I'm not getting this error in eclipse but I can see why you would see a problem. mdao is defined as Dao<Object, Integer> but you are calling getDao(mClass) where mclass is a Class<?>. Object != ? in generic land.

You could turn your entire class into a generic type. Something like the following would work.

public class DatabaseModel<T, ID> {
    private Dao<T, ID> mDao = null;
    private DatabaseHelper mHelper;
    private Class<T> mClass;

    public DatabaseModel(DatabaseHelper h, Class<T> c) {
        mHelper = h;
        mClass = c;
        try {
            mDao = mHelper.getDao(mClass);
        } catch (SQLException e) {
            Debug.e("Can't get dao", e.getStackTrace());
            throw new RuntimeException(e);
        }
    }
}

That should work.

Thanks. The only thing i can not understand, why Idea is not able to compile this, but eclipse cat — z0_0mer, Feb 23 '12 at 21:57
No idea. It may be that Eclipse is just more lenient in this case. — Gray, Feb 23 '12 at 21:58

score 0 · Answer 2 · answered Aug 13 '12 at 16:18

0

In my case, I could circumvent the problem by using getDataDao() instead of getDao().

answered Aug 13 '12 at 16:18

Paul Lammertsma

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Generics compilation error

2 Answers2