initialisation / declaration of variable

[Gaelle Berton]

i stumbled across this in the practice exam book of Sierre Bates

class Wheel{
Wheel(int s){
s = size;
}

int size;
...
}

the code compiles:

Shouldnt the "size" variable be declared before the constructor uses it? why doesnt it matter?
thanks

[shuba gopal]

Hi Gaelle, is size declared before the Wheel constructor is invoked? In that case it shouldnt be a problem you agree? Can you please post the entire program for my understanding. Is it from K & B SCJP 6?

[Gaelle Berton]

yes it is this same exam practice book:

class Wheel{  
Wheel(int s){  
s = size;  
}  
 void spin(){System.out.println(size + "inch wheel spin");}

...
..

public class Bicycle {
public static  void main(String[] args){
Wheel[] wa = {new Wheel(15), new Wheel(17)};
for (Wheel w: wa){w.spin();}
}
}

[shuba gopal]

Gaelle, I tried it

public class Bicycle {   
public static  void main(String[] args){   
Wheel[] wa = {new Wheel(15), new Wheel(17)};   
for (Wheel w: wa){w.spin();}   
}   
}  

class Wheel{     
Wheel(int s){     
s = size;     
}     
 void spin(){System.out.println(size + "inch wheel spin");}  
}
[code=java]

I am getting the following errors:

C:\Javasrc>javac Bicycle.java
Bicycle.java:10: cannot find symbol
symbol  : variable size
location: class Wheel
s = size;
    ^
Bicycle.java:12: cannot find symbol
symbol  : variable size
location: class Wheel
 void spin(){System.out.println(size + "inch wheel spin");}
                                ^
2 errors

[code=java]

The declaration int size is missing in Bicycle. Where does it occur?
I looked thru the pdf version of the book but was not able to find this problem. Can you tell me the chapter/page number. thanks

[Ernest Friedman-Hill]

Shuba, your definition of the "Wheel" class is just missing the declaration of "size" which appears at the bottom of the class, as shown in the first post above; that's the whole point of this thread. All the other stuff you've posted, including your initial request for more code, is just a distraction and is not relevant, so let's just try to stick to the actual question, shall we?

Gaelle, the fact is simply that when the code inside a method or constructor body is compiled, all the members of that class are in scope. They don't need to be forward declared; it's perfectly OK -- and rather common -- for a method to refer to a variable or method which is declared later on in the same class.

[Campbell Ritchie]

Are you sure it's s = size; rather than size = s;?