How to pass a variable from one class to another class?

Question

Hi,
Is it possible to pass a variable from one class to another? For e.g., I need the value of int a for calculation purpose in method doB() but I get an error <identifier> expected. What does the error mean? I know, it's a very, very simple question but once I learn this, I promise to remember it forever. Thank you.
class A {
  int a;
  int doA() {
      a = a + 1;
      return a;
class B {
  int b;
  A r = new A();
  r.a;  // error: <identifier> expected. What does that mean ?
  int doB() {
     int c = b/a;  // error: operator / cannot be applied to a
}Thank you!

Answer 1

elaine_g wrote:
I am wondering why does (r.a) give an error outside the method? What's the reason it only works when used inside the (b/r.a) maths function? This is illegal syntax:
class B {
  int b;
  A r = new A();
  r.a;  //syntax error
}Why? Class definition restricts what you can define within a class to a few things:
class X {
    Y y = new Y(); //defining a field -- okay
    public X() { //defining a constructor -- okay
    void f() { //defining a method -- okay
}... and a few other things, but you can't just write "r.a" there. It also makes no sense -- that expression by itself just accesses a field and does nothing with it -- why bother?
This is also illegal syntax:
int doB() {
      A r = new A();
      r.a;  // error: not a statement
}Again, all "r.a" does on its own is access a field and do nothing with it -- a "noop". Since it has no effect, writing this indicates confusion on the part of the coder, so it classified as a syntax error. There is no reason to write that.