Compile error in Java object conversion

Question

I have a problem and I'm wondering if anyone knows why:

if(n.getInfo() instanceof Token){
   //Token abc = n.getInfo();
  System.out.print("ouch!");
}

when it runs, it prints out ouch!.

However, when I uncomment the line

  Token abc = n.getInfo();

it gives a compile error:

error: incompatible types: Object cannot be converted to Token
        Token abc = n.getInfo();

I don't understand, as it is an instance of Token, so how it cannot be converted to Token?

Thanks.

Just a note; when you're using instanceof it probably means you're doing something not very OO style. I'd say it's a telltale sign to have a good look at your code. — Bono
– Bono, Commented Dec 21, 2014 at 0:08

Elliott Frisch · Accepted Answer · 2014-12-20 23:53:56Z

6

You've tested that it's an instance, you need to add a cast

Token abc = (Token) n.getInfo();

answered Dec 20, 2014 at 23:53

Elliott Frisch

202k20 gold badges166 silver badges265 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

You might want to mention that the giveaway here is the return type delcared for getInfo()...

Donald_W · Accepted Answer · 2014-12-21 00:03:40Z

2

n.getInfo() could be declared to return, for example, Object

Clearly if this was the case, it would be the same as saying:

Object blah = n.getInfo();
Token abc = blah;

And that wouldn't work. To fix it, you would need:

Token abc = (Token)blah;

answered Dec 21, 2014 at 0:03

Donald_W

1,83323 silver badges36 bronze badges