What are OOP's Jargons and Complexities
Xah Lee, 20050128
The Rise of Classes, Methods, Objects
In computer languages, often a function definition looks like this:
subroutine f (x1, x2, ...) {
variables ...
do this or that
}
In advanced languages such as LISP family, it is not uncommon to define
functions inside a function. For example:
subroutine f (x1, x2, ...) {
variables...
subroutine f1 (x1...) {...}
subroutine f2 (x1...) {...}
}
Often these f1 f2 inner functions are used inside f, and are not
relevant outside of f. Such power of the language gradually developed
into a style of programing. For example:
subroutine a_surface () {
coordinatesList = ...;
subroutine translate (distance) {...}
subroutine rotate (angle) {..}
}
Such a style is that the a_surface is no longer viewed as a function.
But instead, a boxed set of functions, centered around a piece of data.
And, all functions for manipulating this piece of data are all embodied
in this function. For example:
subroutine a_surface (arg) {
coordinatesList = ...
subroutine translate (distance) {set coordinatesList to translated
version}
subroutine rotate (angle) {set coordinatesList to rotated version}
subroutine return () {return coordinatesList}
if (no arg) {return coordinatesList}
else { apply arg to coordinatesList }
}
In this way, one uses a_surface as a data, which comes with its owe set
of functions:
mySurface = a_surface();
mySurface(rotate(angle)); // now the surface data has been
rotated
mySurface(translate(distance)); // now its translated
newSurface = mySurface(return())
So now, a_surface is no longer viewed as a subroutine, but a boxed set
of things centered around a piece of data. All functions that work on
the data are included in the boxed set. This paradigm possible in
functional languages has refined so much so that it spread to other
groups and became known as Object Oriented Programing, and complete
languages with new syntax catered to such scheme emerged.
In such languages, instead of writing them like this:
mySurface = a_surface();
mySurface(rotate(angle));
the syntax is changed to like this, for example:
mySurface = new a_surface();
mySurfaceRotated = mySurface.rotate(angle);
In such languages, the super subroutine a_surface is no longer called a
function or subroutine. It is now called a “Class”. And now the
variable holding the function "mySurface = a_surface()" is now called a
“Object”. Subroutines inside the function a_surface() are no longer
called inner-subroutines. They are called “Methods”. The act of
assigning a super-subroutine to a variable is called instantiation.
This style of programing and language have become so fanatical that in
such dedicated languages like Java, everything in the language are
“Classes”. One can no longer just define a variable or subroutine.
Instead, one creates these meta-subroutine “Classes”. Everything
one do are inside Classes. And one assign Classes inside these Classes
to create “Objects”. And one uses “Methods” to manipulate
Objects. In this fashion, even basic primitives like numbers, strings,
and lists are no longer atomic entities. They are now Classes.
For example, in Java, a string is a class String. And inside the class
String, there are Methods to manipulate strings, such as finding the
number of chars, or extracting parts of the string. This can get very
complicated. For example, in Java, there are actually two Classes of
strings: One is String, and the other is StringBuffer. Which one to use
depends on whether you intend to change the data.
So, a simple code like this in normal languages:
a = "a string";
b = "another one";
c = join(a,b);
print c;
or in lisp style
(set a "a string")
(set b "another one")
(set c (join a b))
(print c)
becomes in pure OOP languages:
public class test {
public static void main(String[] args) {
String a = new String("a string");
String b = new String("another one");
StringBuffer c = new StringBuffer(40);
c.append(a); c.append(b);
System.out.println(c.toString());
}
}
Here, the "new String" creates a String object. The "new
StringBuffer(40)" creates the changeable string object StringBuffer,
with room for 40 chars. "append" is a method of StringBuffer. It is
used to join two Strings.
Notice the syntax "c.append(a)", which we can view it as calling a
inner subroutine "append", on a super subroutine that has been assigned
to c, where, the inner subroutine modifies the inner data by appending
a to it.
And in the above Java example, StringBuffer class has another method
"toString()" used to convert this into a String Class, necessary
because System.out.println's parameter requires a String type, not
StringBuffer.
For a example of the complexity of classes and methods, see the Java
documentation for the StringBuffer class at
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/StringBuffer.html
(local copy)
In the same way, numbers in Java have become a formalization of many
classes: Double, Float, Integer, Long... and each has a bunch of
"methods" to operate or convert from one to the other.
Instead of
aNumber = 3;
print aNumber^3;
In Java the programer needs to master the ins and outs of the several
number classes, and decide which one to use. (and if a program later
needs to change from one type of number to another, it is often
cumbersome.)
This Object Oriented Programing style and dedicated languages (such as
C++, Java) have become a fad like wild fire among the programing mass
of ignoramuses in the industry. Partly because of the data-centric new
perspective, partly because the novelty and mysticism of new syntax and
jargonization.
It is especially hyped by the opportunist Sun Microsystems with the
inception of Java, internet, and web applications booms around 1995. At
those times, OOP (and Java) were thought to revolutionize the industry
and solve all software engineering problems, in particular by certain
"reuse of components" concept that was thought to come with OOP.
As part of this new syntax and purity, where everything in a program is
of Classes and Objects and Methods, many complex issues and concept
have arisen in OOP.
We now know that the jargon Class is originally and effectively just a
boxed set of data and subroutines, all defined inside a subroutine. And
the jargon "Object" is just a variable that has been set to this super
subroutine. And the inner subroutines are what's called Methods.
----------
to be continued tomorrow.
This is part of an installment of the article
“What are OOP's Jargons and Complexities”
by Xah Lee, 20050128. The full text is at
http://xahlee.org/Periodic_dosage_dir/t2/oop.html
© Copyright 2005 by Xah Lee. Verbatim duplication of the complete
article for non-profit purposes is granted.
The article is published in the following newsgroups:
comp.lang.c,comp.lang.c++,comp.lang.lisp,comp.unix.programmer
comp.lang.python,comp.lang.perl.misc,comp.lang.scheme,comp.lang.java.programmer
comp.lang.functional,comp.object,comp.software-eng,comp.software.patterns
Xah
[EMAIL PROTECTED]
∑ http://xahlee.org/
--
http://mail.python.org/mailman/listinfo/python-list
