classcastexception

This piece of code irritates me, sometimes it working and some other times it doesn't ! The NamedQuery : (name = "User.findByLogin", query = "SELECT u FROM User u WHERE u.login = :login") public User findByLogin(String login) { Query query = em.createNamedQuery("User.findByLogin"); query.setParameter("login", login); try { return (User) query.getSingleResult(); } catch (javax.persistence.NoResultException ex) { return null; } } The error make me crazy ! Avertissement: EJB5184: A system exception occurred during an invocation on EJB UserFacade , method: public dz.admin.entity.User dz.admin

I get the following exception in Android when clicking a button to take me from an activity to another (I'm new in Android development, so it may not be the brightest of questions): java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.EditText I have tried cleaning the project several times, I've tried the option Fix Project Properties from Android Tools, I've checked my xml for mistakes but I just can't seem to figure this out. I have to mention that the button worked well for some time until this exception occurred. Here is my xml: <RelativeLayout

I am using Solr 4.6.0 and trying to import my data using CachedSqlEntityProcessor , but somehow I end up getting a ClassCastException . Schema <fields> <field name="_version_" type="long" indexed="true" stored="true"/> <field name="id" type="int" indexed="true" stored="true" required="true" multiValued="false" /> <field name="conference" type="string" indexed="true" stored="true" /> <field name="year" type="int" indexed="true" stored="true" /> <field name="doi" type="string" indexed="false" stored="true" /> <field name="text" type="text_en_shingling" indexed="true" stored="true" /> </fields>

given the following code, I have a question: class A{} class B extends A {} class C extends B{} public class Test { public static void main(String[] args) { A a = new A(); A a1=new A(); B b = new B(); // a=b;// ok // b=(B)a;// ClassCastException // a=(A)a1; // ok // a=a1; // ok a=(B)a1; // compiles ok, ClassCastException } } My question is with the line in bold. My understanding is that for the code to compile, it just needs to be satisfied that the classes are in the same hierarchy and as a result it may work (up the tree implicit casting, down the tree requires explicit casting). Whenever I

In java: Base b = new Base(); Derived d = (Derived)b; throws ClassCastException . Why? Why downcasting throws Exception here? I could not figure out the reason. Let me rename your classes to make things more clear. Base -> Animal . Derived -> Cat . Just because you're an Animal doesn't mean you're a Cat . You could be a Dog . That's why it's illegal to cast an Animal into a Cat . On the other hand, is every Cat an Animal ? The answer is "yes". That's why you could write code like this: Animal animal = new Cat(); or Cat cat = new Cat(); Animal animal = cat; Also what's worth noting is you can