Question

I’m finding this kind of overriding after a new in java code very often

classB body
....
    ClassA a = new ClassA(){
@Override 
public void funcion(){
 atributeClassB = whatever 
   } 
 } ;
....

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

Answer 1

It’s called an anonymous local derived class (or “anonymous inner class”, though there’s a difference between just being “inner” and being local [all local classes are inner; not all inner classes are local; more below]). The code within the curly braces forms part of the class definition of the anonymous class.

This

ClassA a = new ClassA(){@Override public void funcion(){ atributeClassB = whatever } } ;

…is effectively equivalent to this:

ClassA a = new SubClassA();

…where SubClassA is defined within the containing class:

class SubClassA extends ClassA {
    @Override public void funcion(){ atributeClassB = whatever }
}

…although there’s a bit more to it than that because the anonymous class in your example is defined within a method (that’s the “local” vs. “inner” thing), more in the various sections starting here.