java - How exactly does the instanceof method work? and why is it not working in my code shown below? -

this question has answer here:

• instanceof - incompatible conditional operand types 3 answers

so have defined main class shown below , have defined words class , sentence class. note program should return false when ran. however, getting "incompatible conditional operand types words , sentence" error when run it. isn't how instanceof operator used or confused? how can program modified run without crashing?

public class main{ public static void main (string[] args){     words example = new words("heyo");     sentence ex = new sentence("wats dog");      system.out.println(example instanceof sentence); } } 

if variable running instanceof on can't of same type class supply operator, code won't compile.

since example of type words, not sub-class or super-class of sentence, instanceof cannot applied on example , sentence.

here's jls 15.20.2 says expression "relationalexpression instanceof referencetype":

if cast of relationalexpression referencetype rejected compile-time error, instanceof relational expression likewise produces compile-time error. in such situation, result of instanceof expression never true.

at run time, result of instanceof operator true if value of relationalexpression not null , reference cast (§15.16) referencetype without raising classcastexception. otherwise result false.