Java generics ? extends Clazz

Question

I'm using spring, hibernate and junit to setup a test class for some of my models.

All of my models extend BaseModel

I have the following function in my testing class:

void printValidation(Set<ConstraintViolation<? extends BaseModel>> v){
        Iterator<ConstraintViolation<? extends BaseModel>> it = v.iterator();
        while (it.hasNext()) {
            ConstraintViolation<? extends BaseModel> violation = it.next();
            l.info("Validation error {}", violation);
        }
    }

I use it like so inside a test case:

eModel = new Entry(); //This class extends BaseModel
Set<ConstraintViolation<? extends BaseModel>> v = validator.validate(eModel);
assertTrue("There should be validation errors...", v.size() > 0);
printValidation(v);

However, I get the following message in Eclipse, and it does not seem to work: Type mismatch: cannot convert from Set<ConstraintViolation<Entry>> to Set<ConstraintViolation<? extends BaseModel>> Set<ConstraintViolation<? extends BaseModel>>

I have a bunch of other tests, and if I make the function take <Entry> instead of <? extends BaseEntry> <? extends BaseEntry> it works. I have a number of models I'm testing like this, and it is sort of the whole point of generics to not have to duplicate this.

What am I missing here, I guess it has something to do with either what validator.validate is returning or something?

** Edited to fix inline code formatting **

Answer 1

@geoand - Almost, here is the working code:

<T extends BaseModel> void printValidation(Set<ConstraintViolation<T>> v){
    Iterator<ConstraintViolation<T>> it = v.iterator();
    while (it.hasNext()) {
        ConstraintViolation<T> violation = it.next();
        l.info("Validation error {}", violation);
    }
}

And the function that does the test:

@Test
public void testEntry() {
    Set<ConstraintViolation<Entry>> v = validator.validate(eModel);
    assertTrue("There should be validation errors...", v.size() > 0);
    printValidation(v);

Answer 2

尝试void <T extends BaseModel> printValidation(Set<ConstraintViolation<T>> v)