CODEWITHSUNDEEP
java
María Belén Esteban Menéndez
María Belén Esteban Menéndez

Reputation: 397

Type safety: Unchecked cast from List to List<String>

I have this method where I cast the results to (List ) , but my eclipse is still complaining ! Type safety: Unchecked cast from List to List

@Override
public List<String> getDevices(Long productId) {

        String queryString = "SELECT op.name FROM t_operation op WHERE op.discriminator = 'ANDROID' and PRODUCT =:productId ";

        try {
            Query query = getEntityManager().createQuery(queryString);
            query.setParameter("productId", productId);

            return (List<String> ) query.getResultList();


        } catch (RuntimeException re) {         
            throw re;
        }

    }

Upvotes: 14

Views: 22128

Answers (4)

Galya
Galya

Reputation: 6364

Please don't use @SuppressWarnings and don't type cast, because these are error-prone ways to do this. Follow the advice given in the following answer to a similar question and use TypedQuery : https://stackoverflow.com/a/21354639/3657198

TypedQuery<SimpleEntity> q = 
    em.createQuery("select t from SimpleEntity t", SimpleEntity.class);

List<SimpleEntity> listOfSimpleEntities = q.getResultList();
for (SimpleEntity entity : listOfSimpleEntities) {
    // do something useful with entity;
}

Upvotes: 8

L&#234; Thọ
L&#234; Thọ

Reputation: 414

You can sure use TypedQuery with the parameter types is String in this case. So what you need is

TypedQuery<String> query = getEntityManager().createQuery(queryString, String.class);

Upvotes: 7

Yassin Hajaj
Yassin Hajaj

Reputation: 21975

You may want to use this special hack to return the correct type. It works with any type of object since String#valueOf(Object) exists

try {
    Query query = getEntityManager().createQuery(queryString);
    query.setParameter("productId", productId);
    return query.getResultList().stream().map(String::valueOf).collect(Collectors.toList());
} catch (RuntimeException re) {         
    throw re;
}

Upvotes: 2

Jordi Castilla
Jordi Castilla

Reputation: 26961

You will get this warning due runtime check cast.

Even if you use if(query.getResultList() instanceof List<?>) you will get this warning, so...

  • use @SuppressWarnings("unchecked") or
  • use generics

Upvotes: 4

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