How it's called the java overriding functions after a new

[gsmorbit.com]

I'm finding this kind of overriding after a new in java code very often \[code\]classB body.... ClassA a = new ClassA(){@Override public void funcion(){ atributeClassB = whatever } } ;....\[/code\]How is it called this kind of constructing ? when is executed the code between brackets ? how this code can have access to a classB attribute ? in fact if i only know how this way of working is called i can document myselve in google but without a key name i couldn't find it.the code where i've found it is this here on line 151