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();
a_surface(rotate(angle)); # now the surface data has been rotated
a_surface(translate(distance)); # now its translated
myNewSurface = a_surface(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 available in
functional languages has refined so much so that it spread to other
groups that it became knows 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();
a_surface(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. They are now called a "Class". And now the
variable "mySurface = a_surface()" is now called a "Object". The
subroutines inside the function a_surface() is no longer called
inner-subroutines. They are called "Methods".
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 variables inside these Classes to
create "Objects". And one uses "Methods" to manipulate Objects. In this
fashion, even data types like numbers, strings, and lists are no longer
atomic data types. 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
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
ignoramus mass 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 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.
-----------------
because of psychological push for purity, in Java there are no longer
plain subroutines. Everything is a method of some class. Standard
functions like opening a file, square root a number, for loop thru a
list, if else branching statements, or simple arithmetic operations...
must now some how become a method of some class. In this way, the OOP
Hierarchy is born.
Basic data types such as now the various classes of numbers, are now
grouped into a Number class hierarchy, each class having their own set
of methods. The characters, string or other data types, are lumped into
one hierarchy class of data types. Many types of lists (variously known
as arrays, vectors, lists, hashes...), are lumped into a one hierarchy,
with each node Classe having their own set methods as appropriate. Math
functions, are lumped into some math class hierarchy.
Now suppose the plus operation +, where does it go? Should it become
methods of the various classes under Number headings, or should it be
methods of the Math class set? Each language deals with these issues
differently. As a example, see this page for the hierarchy of Java's
core language classes:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/package-tree.html
The hierarchy concept is so entangled in pure OOP such that OOP is
erroneously thought of as languages with a hierarchy. (there are now
also so-called Object-Oriented databases that are centered on the
concept of all data are trees ...)
Normally in a program, when we want to do some operation we just call
the subroutine on some data. Such as
open(this_file)
square(4)
But now with the pure OOP style, there can no longer be just a number
or this_file path, because everything now must be a Object. So, the
"this_file", usually being just a string representing the path to a
file on the disk, is now some "file object". Initiated by something
like
this_file = new File("path to file");
where this file class has a bunch of methods such as reading or writing
to it.
see this page for the complexity of the IO tree
http://java.sun.com/j2se/1.4.2/docs/api/java/io/package-tree.html
see this page for the documentation of the File class itself, along
with its 40 or so methods and other things.
http://java.sun.com/j2se/1.4.2/docs/api/java/io/File.html
Tomorrow i shall cover more manmade jargons and complexities arising
out of the OOP hype, in particular Java.
instantiation
initializer, constructor, assessor
access level specifier
abstract class and abstract methods
instance methods and class methods
interface, inheritance, polymorphism.
Xah
[EMAIL PROTECTED]
http://xahlee.org/PageTwo_dir/more.html
--
http://mail.python.org/mailman/listinfo/python-list
