java - When checking for a instance of the current class, why doesn't "x instanceof getClass()" work? -

i have abstract class associativefunction extends expr. there different functions subclasses of associativefunction, , there other expressions subclasses of expr not associativefunction.

in method within associativefunction class, need check if expr object instance of current class or 1 of subclasses,

i.e. product (extends associativefunction) , inherits method; therefore, check should return true product objects , crossproduct (extends product) objects, false sum (extends associativefunction) , number (extends expr) objects.

1. why following not work? how can work using instanceof operator? if can't, why not?

   if (newargs.get(i) instanceof getclass()) { 

   eclipse yields error:

   syntax error on token "instanceof", == expected )

2. this code seems work, correct? why different (1)?

   if (getclass().isinstance(newargs.get(i))) { 

why following not work?

because instanceof requires type name second operand @ compile-time, basically. won't able use instanceof operator.

the production instanceof operator is:

relationalexpression instanceof referencetype

where referencetype classorinterfacetype, typevariable or arraytype... in other words, type name rather expression evaluates class<?> reference. you're doing bit trying declare variable type "the current class" - language isn't defined way.

this code seems work, correct?

yes.

why different (1)?

because it's using class.isinstance method, rather instanceof operator. they're different things. isinstance method more dynamic version.