Why variables have to be final in anonymous methods and class fields don't
anonymous-methods, attributes, java
Solution
The local variable is allocated in the stack, and it will fall out of scope after `testMethod()`. Making the variable final ensures that it is ok to just pass a reference to it to the anonymous class. If it was not final, a later assignment to it in `testMethod()` could change the value later with confusing results. (The user might expect the later assigned value used, but that would be impossible).
A field of the parent class, however can be accessed through the parent reference of the anonymous class, so any later assignments can be handled without confusion.
Problem
If I had this anonymous method I should declare x variable as final. ``` private void testMethod (ListField<BeanModel> listField){ final ListLoader<BeanModel> loader = new PagedListLoader<BeanModel>(); listField.addListener(Events.Attach, new Listener<ListViewEvent<BeanModel>>() { @Override public void handleEvent(ListViewEvent<BeanModel> be) { loader.load(); } }); } ``` However, if loader was a class field, it wouldn't be necessary to declare it as final: ``` public class testClass{ private ListLoader<BeanModel> loader = new PagedListLoader<BeanModel>(); private void testMethod (ListField<BeanModel> listField){ listField.addListener(Events.Attach, new Listener<ListViewEvent<BeanModel>>() { @Override public void handleEvent(ListViewEvent<BeanModel> be) { loader.load(); } }); //Could I modify loader's reference here, before the method executes? //loader = null; } } ``` Does anyone know the reason why they guarantee local variables not to change when they're accessed but don't do it for class fields?