- Schematically,
the things in
a Java program can be
represented by
the following
diagram:
At the top level, you will see the following constructs in a Java program:
- A Java program consist of
one or more classes
- A class contains:
- One or more instance/class variables
- One or more functions (= methods)
- A Java program consist of
one or more classes
- Important property
of Object Oriented Programming Languages:
- The class construct
in OOP (Object Oriented Programming) languages
can restrict the
access of
instance/class variables by
methods in other classes
Example:
Methods in class2 cannot access a private variable in another class !!!
- The class construct
in OOP (Object Oriented Programming) languages
can restrict the
access of
instance/class variables by
methods in other classes
- Data abstraction:
- Since the main( )
function is usually in a
seperate class:
- The private variables
defined in a user-defined class is
inaccessible to
the program statements
in the main( ) function.
I.e.: you can't access the private variables in a class directly using for example:
objVar.privateVarName = ....in main( ).
So these private variables are hidden from the programmer that write the main( ) program....
They call this information hiding by a fancy term:
- Data abstraction
- The private variables
defined in a user-defined class is
inaccessible to
the program statements
in the main( ) function.
- Since the main( )
function is usually in a
seperate class:
- Fact:
- C does not provide any mechanism to associate data (variables) and code (methods/functions)
What this mean is:
- C does not have the class construct that you can use to hide some variables from being access by functions in another class
- Structure of a C program:
- A C program consists of a
collection of
- Data structures/types definitions
- (Global) variables
- Functions (with local variables and statements)
stored in one or more files.
Schematically:
- A C program consists of a
collection of
- C does not
provide access protection
in things:
A function can access any variable that is defined outside a function
-
Note:
- A later revision of
the C programming language (C99)
has added a
construct
(static globals) to
limit the
accessibility of
global variables
We will discuss this later in scoping rules
- A later revision of
the C programming language (C99)
has added a
construct
(static globals) to
limit the
accessibility of
global variables
- Historical note:
- What we now call a method,
was traditionally called:
- a subroutine (or subprogram), or
- a procedure, or
- a function
- What we now call a method,
was traditionally called:
- Personal practice:
- In this course, I was use function instead of method because that's still the common practice in C.