java 类型安全：从 List 到 List<String> 的未经检查的强制转换
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Type safety: Unchecked cast from List to List<String>
提问by María Belén Esteban Menéndez
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
我有这个方法，可以将结果转换为 (List)，但是我的 eclipse 仍然在抱怨！ 类型安全：从列表到列表的未经检查的强制转换
@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;
}
}
采纳答案by Jordi Castilla
You will get this warning due runtime check cast.
由于运行时检查转换，您将收到此警告。
Even if you use if(query.getResultList() instanceof List<?>)you will get this warning, so...
即使你使用if(query.getResultList() instanceof List<?>)你也会收到这个警告，所以......
- use
@SuppressWarnings("unchecked")or - use generics
- 使用
@SuppressWarnings("unchecked")或 - 使用泛型
回答by Lê Th?
You can sure use TypedQuery with the parameter types is String in this case. So what you need is
在这种情况下，您可以确定将 TypedQuery 与参数类型一起使用。所以你需要的是
TypedQuery<String> query = getEntityManager().createQuery(queryString, String.class);
回答by Galya
Please don't use @SuppressWarningsand 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
请不要使用@SuppressWarnings也不要类型转换，因为这些是容易出错的方法。按照以下对类似问题的回答中给出的建议并使用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;
}
回答by Yassin Hajaj
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
你可能想使用这个特殊的技巧来返回正确的类型。它适用于任何类型的对象，因为它String#valueOf(Object)存在
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;
}
