Static method related

[N Sam]

Book says static methods can not access object instance variables. But the following code successfully prints out
ba.balance = 10
instance var = 5.

It seems like Static method is able to access the instance variable of another class, as well as the instance variable of main class. What gives ?

        class InitProcess {
             public static void main(String[] args) {                
                 mymethod();
             }
             int x = 5;

             static int mymethod() {
                 BankAcct ba = new BankAcct();
                 System.out.println(" ba.balance = " + ba.balance);
                 InitProcess ip = new InitProcess();
                 System.out.println("instance var = " + ip.x);  
                 return ba.balance;
             }
             
         }

class BankAcct {
        int   balance;
        BankAcct ()  {
             balance = 10;
        }
}

[Henry Wong]

N Sam wrote:Book says static methods can not access object instance variables. But the following code successfully prints out
ba.balance = 10
instance var = 5.

It seems like Static method is able to access the instance variable of another class, as well as the instance variable of main class. What gives ?

Static methods can't access instance variable via the this reference -- because it is in a static context. Where did you learn that it can't access any instance variables?

Henry

[N Sam]

It is from the OCA exam book (by Mala Gupta) that i am reading, page 52:
"static methods aren't associated with objects and can't use any of the instance variables of a class".

But I suspect this is not true, based on my code. Static method is behaving just like regular method.

[Campbell Ritchie]

No, classes don't have instance fields. Objects do. What you are doing is creating an object ba (or ip) and using that to access its fields.

[Campbell Ritchie]

A few minutes ago, I wrote:No, classes don't have instance fields. Objects do. . . .

That is not quite accurate.

[N Sam]

I will also post this question on the OCA forum and see if it elicits any answers. Question still remains open.

[Jeanne Boyarsky]

I think that is an English thing. This code is fine because it references the instance variable balance on the ba instance of BankAccount.

static int mymethod() {  
  BankAcct ba = new BankAcct();  
  return ba.balance;  
}

This code gives an error because a static method is trying to reference an instance variable and that isn't allowed.

static int mymethod() {  
  return balance;  
}