<s>
Object-oriented	B-Language
programming	I-Language
(	O
OOP	O
)	O
is	O
a	O
programming	O
paradigm	O
based	O
on	O
the	O
concept	O
of	O
"	O
objects	O
"	O
,	O
which	O
can	O
contain	O
data	O
and	O
code	B-Application
.	O
</s>
<s>
The	O
data	O
is	O
in	O
the	O
form	O
of	O
fields	B-Application
(	O
often	O
known	O
as	O
attributes	B-General_Concept
or	O
properties	O
)	O
,	O
and	O
the	O
code	B-Application
is	O
in	O
the	O
form	O
of	O
procedures	O
(	O
often	O
known	O
as	O
methods	B-Language
)	O
.	O
</s>
<s>
A	O
common	O
feature	O
of	O
objects	O
is	O
that	O
procedures	O
(	O
or	O
methods	B-Language
)	O
are	O
attached	O
to	O
them	O
and	O
can	O
access	O
and	O
modify	O
the	O
object	B-Device
's	O
data	B-Application
fields	I-Application
.	O
</s>
<s>
In	O
this	O
brand	O
of	O
OOP	O
,	O
there	O
is	O
usually	O
a	O
special	O
name	O
such	O
as	O
or	O
used	O
to	O
refer	O
to	O
the	O
current	O
object	B-Device
.	O
</s>
<s>
In	O
OOP	O
,	O
computer	B-Application
programs	I-Application
are	O
designed	O
by	O
making	O
them	O
out	O
of	O
objects	O
that	O
interact	O
with	O
one	O
another	O
.	O
</s>
<s>
OOP	O
languages	O
are	O
diverse	O
,	O
but	O
the	O
most	O
popular	O
ones	O
are	O
class-based	B-Application
,	O
meaning	O
that	O
objects	O
are	O
instances	O
of	O
classes	B-Application
,	O
which	O
also	O
determine	O
their	O
types	O
.	O
</s>
<s>
Many	O
of	O
the	O
most	O
widely	O
used	O
programming	O
languages	O
(	O
such	O
as	O
C++	B-Language
,	O
Java	B-Language
,	O
Python	B-Language
,	O
etc	O
.	O
)	O
</s>
<s>
are	O
multi-paradigm	O
and	O
they	O
support	O
object-oriented	B-Language
programming	I-Language
to	O
a	O
greater	O
or	O
lesser	O
degree	O
,	O
typically	O
in	O
combination	O
with	O
imperative	B-Application
,	O
procedural	B-Application
programming	I-Application
.	O
</s>
<s>
Significant	O
object-oriented	B-Language
languages	I-Language
include	O
:	O
Ada	B-Language
,	O
ActionScript	B-Operating_System
,	O
C++	B-Language
,	O
Common	B-Language
Lisp	I-Language
,	O
C#	B-Application
,	O
Dart	B-Language
,	O
Eiffel	B-Language
,	O
Fortran	B-Application
2003	I-Application
,	O
Haxe	B-Language
,	O
Java	B-Language
,	O
JavaScript	B-Language
,	O
Kotlin	B-Language
,	O
logo	B-Device
,	O
MATLAB	B-Language
,	O
Objective-C	B-Language
,	O
Object	B-Language
Pascal	I-Language
,	O
Perl	B-Language
,	O
PHP	B-Application
,	O
Python	B-Language
,	O
R	B-Language
,	O
Raku	B-Application
,	O
Ruby	B-Language
,	O
Scala	B-Application
,	O
SIMSCRIPT	B-Language
,	O
Simula	B-Language
,	O
Smalltalk	B-Application
,	O
Swift	B-Application
,	O
Vala	B-Language
and	O
Visual	B-Language
Basic.NET	I-Language
.	O
</s>
<s>
Terminology	O
invoking	O
"	O
objects	O
"	O
and	O
"	O
oriented	O
"	O
in	O
the	O
modern	O
sense	O
of	O
object-oriented	B-Language
programming	I-Language
made	O
its	O
first	O
appearance	O
at	O
MIT	O
in	O
the	O
late	O
1950s	O
and	O
early	O
1960s	O
.	O
</s>
<s>
In	O
the	O
environment	O
of	O
the	B-Application
artificial	I-Application
intelligence	I-Application
group	O
,	O
as	O
early	O
as	O
1960	O
,	O
"	O
object	B-Device
"	O
could	O
refer	O
to	O
identified	O
items	O
(	O
LISP	B-Language
atoms	I-Language
)	O
with	O
properties	O
(	O
attributes	B-General_Concept
)	O
;	O
</s>
<s>
Alan	O
Kay	O
later	O
cited	O
a	O
detailed	O
understanding	O
of	O
LISP	B-Language
internals	O
as	O
a	O
strong	O
influence	O
on	O
his	O
thinking	O
in	O
1966	O
.	O
</s>
<s>
Another	O
early	O
MIT	O
example	O
was	O
Sketchpad	B-Application
created	O
by	O
Ivan	O
Sutherland	O
in	O
1960	O
–	O
1961	O
;	O
in	O
the	O
glossary	O
of	O
the	O
1963	O
technical	O
report	O
based	O
on	O
his	O
dissertation	O
about	O
Sketchpad	B-Application
,	O
Sutherland	O
defined	O
notions	O
of	O
"	O
object	B-Device
"	O
and	O
"	O
instance	O
"	O
(	O
with	O
the	O
class	O
concept	O
covered	O
by	O
"	O
master	O
"	O
or	O
"	O
definition	O
"	O
)	O
,	O
albeit	O
specialized	O
to	O
graphical	O
interaction	O
.	O
</s>
<s>
Also	O
,	O
an	O
MIT	O
ALGOL	B-Language
version	O
,	O
AED-0	O
,	O
established	O
a	O
direct	O
link	O
between	O
data	B-General_Concept
structures	I-General_Concept
(	O
"	O
plexes	O
"	O
,	O
in	O
that	O
dialect	O
)	O
and	O
procedures	O
,	O
prefiguring	O
what	O
were	O
later	O
termed	O
"	O
messages	O
"	O
,	O
"	O
methods	B-Language
"	O
,	O
and	O
"	O
member	O
functions	B-Language
"	O
.	O
</s>
<s>
Simula	B-Language
introduced	O
important	O
concepts	O
that	O
are	O
today	O
an	O
essential	O
part	O
of	O
object-oriented	B-Language
programming	I-Language
,	O
such	O
as	O
class	O
and	O
object	B-Device
,	O
inheritance	B-Language
,	O
and	O
dynamic	O
binding	O
.	O
</s>
<s>
The	O
object-oriented	B-Language
Simula	B-Language
programming	I-Language
language	I-Language
was	O
used	O
mainly	O
by	O
researchers	O
involved	O
with	O
physical	O
modelling	O
,	O
such	O
as	O
models	O
to	O
study	O
and	O
improve	O
the	O
movement	O
of	O
ships	O
and	O
their	O
content	O
through	O
cargo	O
ports	O
.	O
</s>
<s>
In	O
the	O
1970s	O
,	O
the	O
first	O
version	O
of	O
the	O
Smalltalk	B-Application
programming	I-Application
language	I-Application
was	O
developed	O
at	O
Xerox	O
PARC	O
by	O
Alan	O
Kay	O
,	O
Dan	O
Ingalls	O
and	O
Adele	O
Goldberg	O
.	O
</s>
<s>
Smalltalk-72	B-Application
included	O
a	O
programming	B-Application
environment	I-Application
and	O
was	O
dynamically	B-Algorithm
typed	I-Algorithm
,	O
and	O
at	O
first	O
was	O
interpreted	B-Application
,	O
not	O
compiled	B-Language
.	O
</s>
<s>
Smalltalk	B-Application
became	O
noted	O
for	O
its	O
application	O
of	O
object	B-Device
orientation	O
at	O
the	O
language-level	O
and	O
its	O
graphical	O
development	O
environment	O
.	O
</s>
<s>
Smalltalk	B-Application
went	O
through	O
various	O
versions	O
and	O
interest	O
in	O
the	O
language	O
grew	O
.	O
</s>
<s>
While	O
Smalltalk	B-Application
was	O
influenced	O
by	O
the	O
ideas	O
introduced	O
in	O
Simula	B-Language
67	I-Language
it	O
was	O
designed	O
to	O
be	O
a	O
fully	O
dynamic	O
system	O
in	O
which	O
classes	B-Application
could	O
be	O
created	O
and	O
modified	O
dynamically	O
.	O
</s>
<s>
In	O
the	O
1970s	O
,	O
Smalltalk	B-Application
influenced	O
the	O
Lisp	B-Language
community	O
to	O
incorporate	O
object-based	B-Application
techniques	O
that	O
were	O
introduced	O
to	O
developers	O
via	O
the	O
Lisp	B-Operating_System
machine	I-Operating_System
.	O
</s>
<s>
Experimentation	O
with	O
various	O
extensions	O
to	O
Lisp	B-Language
(	O
such	O
as	O
LOOPS	O
and	O
Flavors	B-Language
introducing	O
multiple	B-Application
inheritance	I-Application
and	O
mixins	B-Language
)	O
eventually	O
led	O
to	O
the	O
Common	B-Application
Lisp	I-Application
Object	I-Application
System	I-Application
,	O
which	O
integrates	O
functional	B-Language
programming	I-Language
and	O
object-oriented	B-Language
programming	I-Language
and	O
allows	O
extension	O
via	O
a	O
Meta-object	O
protocol	O
.	O
</s>
<s>
Examples	O
include	O
the	O
Intel	B-Device
iAPX	I-Device
432	I-Device
and	O
the	O
Linn	B-General_Concept
Smart	I-General_Concept
Rekursiv	I-General_Concept
.	O
</s>
<s>
In	O
1981	O
,	O
Goldberg	O
edited	O
the	O
August	O
issue	O
of	O
Byte	O
Magazine	O
,	O
introducing	O
Smalltalk	B-Application
and	O
object-oriented	B-Language
programming	I-Language
to	O
a	O
wider	O
audience	O
.	O
</s>
<s>
In	O
1986	O
,	O
the	O
Association	O
for	O
Computing	O
Machinery	O
organised	O
the	O
first	O
Conference	O
on	O
Object-Oriented	B-Language
Programming	I-Language
,	O
Systems	O
,	O
Languages	O
,	O
and	O
Applications	O
(	O
OOPSLA	O
)	O
,	O
which	O
was	O
unexpectedly	O
attended	O
by	O
1,000	O
people	O
.	O
</s>
<s>
In	O
the	O
mid-1980s	O
Objective-C	B-Language
was	O
developed	O
by	O
Brad	O
Cox	O
,	O
who	O
had	O
used	O
Smalltalk	B-Application
at	O
ITT	O
Inc.	O
,	O
and	O
Bjarne	O
Stroustrup	O
,	O
who	O
had	O
used	O
Simula	B-Language
for	O
his	O
PhD	O
thesis	O
,	O
eventually	O
went	O
to	O
create	O
the	O
object-oriented	B-Language
C++	B-Language
.	O
</s>
<s>
In	O
1985	O
,	O
Bertrand	O
Meyer	O
also	O
produced	O
the	O
first	O
design	O
of	O
the	O
Eiffel	B-Language
language	I-Language
.	O
</s>
<s>
Focused	O
on	O
software	O
quality	O
,	O
Eiffel	B-Language
is	O
a	O
purely	O
object-oriented	B-Language
programming	I-Language
language	I-Language
and	O
a	O
notation	O
supporting	O
the	O
entire	O
software	O
lifecycle	O
.	O
</s>
<s>
Meyer	O
described	O
the	O
Eiffel	B-Language
software	O
development	O
method	O
,	O
based	O
on	O
a	O
small	O
number	O
of	O
key	O
ideas	O
from	O
software	O
engineering	O
and	O
computer	O
science	O
,	O
in	O
Object-Oriented	B-Language
Software	O
Construction	O
.	O
</s>
<s>
Essential	O
to	O
the	O
quality	O
focus	O
of	O
Eiffel	B-Language
is	O
Meyer	O
's	O
reliability	O
mechanism	O
,	O
Design	B-Application
by	I-Application
Contract	I-Application
,	O
which	O
is	O
an	O
integral	O
part	O
of	O
both	O
the	O
method	O
and	O
language	O
.	O
</s>
<s>
In	O
the	O
early	O
and	O
mid-1990s	O
object-oriented	B-Language
programming	I-Language
developed	O
as	O
the	O
dominant	O
programming	O
paradigm	O
when	O
programming	O
languages	O
supporting	O
the	O
techniques	O
became	O
widely	O
available	O
.	O
</s>
<s>
These	O
included	O
Visual	B-Application
FoxPro	I-Application
3.0	O
,	O
C++	B-Language
,	O
and	O
Delphi	B-Language
.	O
</s>
<s>
Its	O
dominance	O
was	O
further	O
enhanced	O
by	O
the	O
rising	O
popularity	O
of	O
graphical	B-Application
user	I-Application
interfaces	I-Application
,	O
which	O
rely	O
heavily	O
upon	O
object-oriented	B-Language
programming	I-Language
techniques	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
closely	O
related	O
dynamic	O
GUI	B-Application
library	O
and	O
OOP	O
language	O
can	O
be	O
found	O
in	O
the	O
Cocoa	B-Operating_System
frameworks	O
on	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
,	O
written	O
in	O
Objective-C	B-Language
,	O
an	O
object-oriented	B-Language
,	O
dynamic	O
messaging	O
extension	O
to	O
C	B-Language
based	O
on	O
Smalltalk	B-Application
.	O
</s>
<s>
OOP	O
toolkits	O
also	O
enhanced	O
the	O
popularity	O
of	O
event-driven	B-Application
programming	I-Application
(	O
although	O
this	O
concept	O
is	O
not	O
limited	O
to	O
OOP	O
)	O
.	O
</s>
<s>
At	O
ETH	O
Zürich	O
,	O
Niklaus	O
Wirth	O
and	O
his	O
colleagues	O
had	O
also	O
been	O
investigating	O
such	O
topics	O
as	O
data	B-Application
abstraction	I-Application
and	O
modular	B-Architecture
programming	I-Architecture
(	O
although	O
this	O
had	O
been	O
in	O
common	O
use	O
in	O
the	O
1960s	O
or	O
earlier	O
)	O
.	O
</s>
<s>
Modula-2	B-Language
(	O
1978	O
)	O
included	O
both	O
,	O
and	O
their	O
succeeding	O
design	O
,	O
Oberon	B-Language
,	O
included	O
a	O
distinctive	O
approach	O
to	O
object	B-Device
orientation	O
,	O
classes	B-Application
,	O
and	O
such	O
.	O
</s>
<s>
Object-oriented	B-Language
features	O
have	O
been	O
added	O
to	O
many	O
previously	O
existing	O
languages	O
,	O
including	O
Ada	B-Language
,	O
BASIC	O
,	O
Fortran	B-Application
,	O
Pascal	B-Application
,	O
and	O
COBOL	B-Application
.	O
</s>
<s>
Adding	O
these	O
features	O
to	O
languages	O
that	O
were	O
not	O
initially	O
designed	O
for	O
them	O
often	O
led	O
to	O
problems	O
with	O
compatibility	O
and	O
maintainability	O
of	O
code	B-Application
.	O
</s>
<s>
More	O
recently	O
,	O
a	O
number	O
of	O
languages	O
have	O
emerged	O
that	O
are	O
primarily	O
object-oriented	B-Language
,	O
but	O
that	O
are	O
also	O
compatible	O
with	O
procedural	B-Application
methodology	O
.	O
</s>
<s>
Two	O
such	O
languages	O
are	O
Python	B-Language
and	O
Ruby	B-Language
.	O
</s>
<s>
Probably	O
the	O
most	O
commercially	O
important	O
recent	O
object-oriented	B-Language
languages	I-Language
are	O
Java	B-Language
,	O
developed	O
by	O
Sun	O
Microsystems	O
,	O
as	O
well	O
as	O
C#	B-Application
and	O
Visual	B-Language
Basic.NET	I-Language
(	O
VB.NET	B-Language
)	O
,	O
both	O
designed	O
for	O
Microsoft	O
's	O
.NET	B-Application
platform	I-Application
.	O
</s>
<s>
Each	O
of	O
these	O
two	O
frameworks	O
shows	O
,	O
in	O
its	O
own	O
way	O
,	O
the	O
benefit	O
of	O
using	O
OOP	O
by	O
creating	O
an	O
abstraction	B-Application
from	O
implementation	O
.	O
</s>
<s>
VB.NET	B-Language
and	O
C#	B-Application
support	O
cross-language	O
inheritance	B-Language
,	O
allowing	O
classes	B-Application
defined	O
in	O
one	O
language	O
to	O
subclass	O
classes	B-Application
defined	O
in	O
the	O
other	O
language	O
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
uses	O
objects	O
,	O
but	O
not	O
all	O
of	O
the	O
associated	O
techniques	O
and	O
structures	O
are	O
supported	O
directly	O
in	O
languages	O
that	O
claim	O
to	O
support	O
OOP	O
.	O
</s>
<s>
The	O
features	O
listed	O
below	O
are	O
common	O
among	O
languages	O
considered	O
to	O
be	O
strongly	O
class	O
-	O
and	O
object-oriented	B-Language
(	O
or	O
multi-paradigm	O
with	O
OOP	O
support	O
)	O
,	O
with	O
notable	O
exceptions	O
mentioned	O
.	O
</s>
<s>
This	O
may	O
include	O
data	B-General_Concept
structures	I-General_Concept
like	O
strings	O
,	O
lists	O
,	O
and	O
hash	B-Algorithm
tables	I-Algorithm
that	O
are	O
either	O
built-in	O
or	O
result	O
from	O
combining	O
variables	O
using	O
memory	O
pointers	O
.	O
</s>
<s>
Procedures	O
–	O
also	O
known	O
as	O
functions	B-Language
,	O
methods	B-Language
,	O
routines	O
,	O
or	O
subroutines	O
–	O
that	O
take	O
input	O
,	O
generate	O
output	O
,	O
and	O
manipulate	O
data	O
.	O
</s>
<s>
Modern	O
languages	O
include	O
structured	B-Language
programming	I-Language
constructs	O
like	O
loops	O
and	O
conditionals	B-Language
.	O
</s>
<s>
Modular	B-Architecture
programming	I-Architecture
support	O
provides	O
the	O
ability	O
to	O
group	O
procedures	O
into	O
files	O
and	O
modules	B-Architecture
for	O
organizational	O
purposes	O
.	O
</s>
<s>
Modules	B-Architecture
are	O
namespaced	O
so	O
identifiers	O
in	O
one	O
module	B-Architecture
will	O
not	O
conflict	O
with	O
a	O
procedure	O
or	O
variable	O
sharing	O
the	O
same	O
name	O
in	O
another	O
file	O
or	O
module	B-Architecture
.	O
</s>
<s>
Languages	O
that	O
support	O
object-oriented	B-Language
programming	I-Language
(	O
OOP	O
)	O
typically	O
use	O
inheritance	B-Language
for	O
code	B-Application
reuse	O
and	O
extensibility	O
in	O
the	O
form	O
of	O
either	O
classes	B-Application
or	O
prototypes	B-Application
.	O
</s>
<s>
Those	O
that	O
use	O
classes	B-Application
support	O
two	O
main	O
concepts	O
:	O
</s>
<s>
Classes	B-Application
–	O
the	O
definitions	O
for	O
the	O
data	O
format	O
and	O
available	O
procedures	O
for	O
a	O
given	O
type	O
or	O
class	O
of	O
object	B-Device
;	O
may	O
also	O
contain	O
data	O
and	O
procedures	O
(	O
known	O
as	O
class	O
methods	B-Language
)	O
themselves	O
,	O
i.e.	O
</s>
<s>
Sometimes	O
objects	O
represent	O
more	O
abstract	O
entities	O
,	O
like	O
an	O
object	B-Device
that	O
represents	O
an	O
open	O
file	O
,	O
or	O
an	O
object	B-Device
that	O
provides	O
the	O
service	O
of	O
translating	O
measurements	O
from	O
U.S.	O
customary	O
to	O
metric	O
.	O
</s>
<s>
Each	O
object	B-Device
is	O
said	O
to	O
be	O
an	O
instance	O
of	O
a	O
particular	O
class	O
(	O
for	O
example	O
,	O
an	O
object	B-Device
with	O
its	O
name	O
field	O
set	O
to	O
"	O
Mary	O
"	O
might	O
be	O
an	O
instance	O
of	O
class	O
Employee	O
)	O
.	O
</s>
<s>
Procedures	O
in	O
object-oriented	B-Language
programming	I-Language
are	O
known	O
as	O
methods	B-Language
;	O
variables	O
are	O
also	O
known	O
as	O
fields	B-Application
,	O
members	O
,	O
attributes	B-General_Concept
,	O
or	O
properties	O
.	O
</s>
<s>
Objects	O
are	O
accessed	O
somewhat	O
like	O
variables	O
with	O
complex	O
internal	O
structure	O
,	O
and	O
in	O
many	O
languages	O
are	O
effectively	O
pointers	O
,	O
serving	O
as	O
actual	O
references	O
to	O
a	O
single	O
instance	O
of	O
said	O
object	B-Device
in	O
memory	O
within	O
a	O
heap	O
or	O
stack	O
.	O
</s>
<s>
They	O
provide	O
a	O
layer	O
of	O
abstraction	B-Application
which	O
can	O
be	O
used	O
to	O
separate	O
internal	O
from	O
external	O
code	B-Application
.	O
</s>
<s>
External	O
code	B-Application
can	O
use	O
an	O
object	B-Device
by	O
calling	O
a	O
specific	O
instance	B-Language
method	I-Language
with	O
a	O
certain	O
set	O
of	O
input	O
parameters	O
,	O
read	O
an	O
instance	B-Application
variable	I-Application
,	O
or	O
write	O
to	O
an	O
instance	B-Application
variable	I-Application
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
that	O
uses	O
classes	B-Application
is	O
sometimes	O
called	O
class-based	B-Application
programming	I-Application
,	O
while	O
prototype-based	B-Application
programming	I-Application
does	O
not	O
typically	O
use	O
classes	B-Application
.	O
</s>
<s>
As	O
a	O
result	O
,	O
significantly	O
different	O
yet	O
analogous	O
terminology	O
is	O
used	O
to	O
define	O
the	O
concepts	O
of	O
object	B-Device
and	O
instance	O
.	O
</s>
<s>
In	O
some	O
languages	O
classes	B-Application
and	O
objects	O
can	O
be	O
composed	O
using	O
other	O
concepts	O
like	O
traits	O
and	O
mixins	B-Language
.	O
</s>
<s>
In	O
class-based	B-Application
languages	I-Application
the	O
classes	B-Application
are	O
defined	O
beforehand	O
and	O
the	O
objects	O
are	O
instantiated	O
based	O
on	O
the	O
classes	B-Application
.	O
</s>
<s>
a	O
programmer	O
can	O
expect	O
the	O
existence	O
of	O
the	O
same	O
attributes	B-General_Concept
such	O
as	O
color	O
or	O
sugar_content	O
or	O
is_ripe	O
.	O
</s>
<s>
In	O
prototype-based	B-Application
languages	I-Application
the	O
objects	O
are	O
the	O
primary	O
entities	O
.	O
</s>
<s>
No	O
classes	B-Application
even	O
exist	O
.	O
</s>
<s>
The	O
prototype	O
of	O
an	O
object	B-Device
is	O
just	O
another	O
object	B-Device
to	O
which	O
the	O
object	B-Device
is	O
linked	O
.	O
</s>
<s>
Every	O
object	B-Device
has	O
one	O
prototype	O
link	O
(	O
and	O
only	O
one	O
)	O
.	O
</s>
<s>
You	O
may	O
call	O
two	O
different	O
objects	O
apple	O
and	O
orange	O
a	O
fruit	O
,	O
if	O
the	O
object	B-Device
fruit	O
exists	O
,	O
and	O
both	O
apple	O
and	O
orange	O
have	O
fruit	O
as	O
their	O
prototype	O
.	O
</s>
<s>
The	O
attributes	B-General_Concept
and	O
methods	B-Language
of	O
the	O
prototype	O
are	O
delegated	B-Application
to	O
all	O
the	O
objects	O
of	O
the	O
equivalence	O
class	O
defined	O
by	O
this	O
prototype	O
.	O
</s>
<s>
The	O
attributes	B-General_Concept
and	O
methods	B-Language
owned	O
individually	O
by	O
the	O
object	B-Device
may	O
not	O
be	O
shared	O
by	O
other	O
objects	O
of	O
the	O
same	O
equivalence	O
class	O
;	O
e.g.	O
</s>
<s>
Only	O
single	O
inheritance	B-Language
can	O
be	O
implemented	O
through	O
the	O
prototype	O
.	O
</s>
<s>
It	O
is	O
the	O
responsibility	O
of	O
the	O
object	B-Device
,	O
not	O
any	O
external	O
code	B-Application
,	O
to	O
select	O
the	O
procedural	B-Application
code	I-Application
to	O
execute	O
in	O
response	O
to	O
a	O
method	B-Language
call	I-Language
,	O
typically	O
by	O
looking	O
up	O
the	O
method	O
at	O
run	O
time	O
in	O
a	O
table	O
associated	O
with	O
the	O
object	B-Device
.	O
</s>
<s>
If	O
the	O
call	O
variability	O
relies	O
on	O
more	O
than	O
the	O
single	O
type	O
of	O
the	O
object	B-Device
on	O
which	O
it	O
is	O
called	O
(	O
i.e.	O
</s>
<s>
at	O
least	O
one	O
other	O
parameter	O
object	B-Device
is	O
involved	O
in	O
the	O
method	O
choice	O
)	O
,	O
one	O
speaks	O
of	O
multiple	O
dispatch	O
.	O
</s>
<s>
A	O
method	B-Language
call	I-Language
is	O
also	O
known	O
as	O
message	B-Architecture
passing	I-Architecture
.	O
</s>
<s>
It	O
is	O
conceptualized	O
as	O
a	O
message	O
(	O
the	O
name	O
of	O
the	O
method	O
and	O
its	O
input	O
parameters	O
)	O
being	O
passed	O
to	O
the	O
object	B-Device
for	O
dispatch	O
.	O
</s>
<s>
Data	B-Application
abstraction	I-Application
is	O
a	O
design	O
pattern	O
in	O
which	O
data	O
are	O
visible	O
only	O
to	O
semantically	O
related	O
functions	B-Language
,	O
so	O
as	O
to	O
prevent	O
misuse	O
.	O
</s>
<s>
The	O
success	O
of	O
data	B-Application
abstraction	I-Application
leads	O
to	O
frequent	O
incorporation	O
of	O
data	B-Application
hiding	I-Application
as	O
a	O
design	O
principle	O
in	O
object	B-Language
oriented	I-Language
and	O
pure	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
If	O
a	O
class	O
does	O
not	O
allow	O
calling	O
code	B-Application
to	O
access	O
internal	O
object	B-Device
data	O
and	O
permits	O
access	O
through	O
methods	B-Language
only	O
,	O
this	O
is	O
a	O
form	O
of	O
information	B-Application
hiding	I-Application
known	O
as	O
abstraction	B-Application
.	O
</s>
<s>
Some	O
languages	O
(	O
Java	B-Language
,	O
for	O
example	O
)	O
let	O
classes	B-Application
enforce	O
access	O
restrictions	O
explicitly	O
,	O
for	O
example	O
denoting	O
internal	O
data	O
with	O
the	O
private	O
keyword	O
and	O
designating	O
methods	B-Language
intended	O
for	O
use	O
by	O
code	B-Application
outside	O
the	O
class	O
with	O
the	O
public	O
keyword	O
.	O
</s>
<s>
Methods	B-Language
may	O
also	O
be	O
designed	O
public	O
,	O
private	O
,	O
or	O
intermediate	O
levels	O
such	O
as	O
protected	O
(	O
which	O
allows	O
access	O
from	O
the	O
same	O
class	O
and	O
its	O
subclasses	O
,	O
but	O
not	O
objects	O
of	O
a	O
different	O
class	O
)	O
.	O
</s>
<s>
In	O
other	O
languages	O
(	O
like	O
Python	B-Language
)	O
this	O
is	O
enforced	O
only	O
by	O
convention	O
(	O
for	O
example	O
,	O
private	O
methods	B-Language
may	O
have	O
names	O
that	O
start	O
with	O
an	O
underscore	O
)	O
.	O
</s>
<s>
In	O
C#	B-Application
,	O
Swift	B-Application
&	O
Kotlin	B-Language
languages	O
,	O
internal	O
keyword	O
permits	O
access	O
only	O
to	O
files	O
present	O
in	O
same	O
assembly	O
,	O
package	O
or	O
module	B-Architecture
as	O
that	O
of	O
the	O
class	O
.	O
</s>
<s>
Encapsulation	B-Application
prevents	O
external	O
code	B-Application
from	O
being	O
concerned	O
with	O
the	O
internal	O
workings	O
of	O
an	O
object	B-Device
.	O
</s>
<s>
This	O
facilitates	O
code	B-Application
refactoring	O
,	O
for	O
example	O
allowing	O
the	O
author	O
of	O
the	O
class	O
to	O
change	O
how	O
objects	O
of	O
that	O
class	O
represent	O
their	O
data	O
internally	O
without	O
changing	O
any	O
external	O
code	B-Application
(	O
as	O
long	O
as	O
"	O
public	O
"	O
method	B-Language
calls	I-Language
work	O
the	O
same	O
way	O
)	O
.	O
</s>
<s>
It	O
also	O
encourages	O
programmers	O
to	O
put	O
all	O
the	O
code	B-Application
that	O
is	O
concerned	O
with	O
a	O
certain	O
set	O
of	O
data	O
in	O
the	O
same	O
class	O
,	O
which	O
organizes	O
it	O
for	O
easy	O
comprehension	O
by	O
other	O
programmers	O
.	O
</s>
<s>
Encapsulation	B-Application
is	O
a	O
technique	O
that	O
encourages	O
decoupling	B-Application
.	O
</s>
<s>
Objects	O
can	O
contain	O
other	O
objects	O
in	O
their	O
instance	B-Application
variables	I-Application
;	O
this	O
is	O
known	O
as	O
object	B-Language
composition	I-Language
.	O
</s>
<s>
For	O
example	O
,	O
an	O
object	B-Device
in	O
the	O
Employee	O
class	O
might	O
contain	O
(	O
either	O
directly	O
or	O
through	O
a	O
pointer	O
)	O
an	O
object	B-Device
in	O
the	O
Address	O
class	O
,	O
in	O
addition	O
to	O
its	O
own	O
instance	B-Application
variables	I-Application
like	O
"	O
first_name	O
"	O
and	O
"	O
position	O
"	O
.	O
</s>
<s>
Object	B-Language
composition	I-Language
is	O
used	O
to	O
represent	O
"	O
has-a	O
"	O
relationships	O
:	O
every	O
employee	O
has	O
an	O
address	O
,	O
so	O
every	O
Employee	O
object	B-Device
has	O
access	O
to	O
a	O
place	O
to	O
store	O
an	O
Address	O
object	B-Device
(	O
either	O
directly	O
embedded	O
within	O
itself	O
,	O
or	O
at	O
a	O
separate	O
location	O
addressed	O
via	O
a	O
pointer	O
)	O
.	O
</s>
<s>
Languages	O
that	O
support	O
classes	B-Application
almost	O
always	O
support	O
inheritance	B-Language
.	O
</s>
<s>
This	O
allows	O
classes	B-Application
to	O
be	O
arranged	O
in	O
a	O
hierarchy	O
that	O
represents	O
"	O
is-a-type-of	O
"	O
relationships	O
.	O
</s>
<s>
All	O
the	O
data	O
and	O
methods	B-Language
available	O
to	O
the	O
parent	O
class	O
also	O
appear	O
in	O
the	O
child	O
class	O
with	O
the	O
same	O
names	O
.	O
</s>
<s>
Subclasses	O
can	O
override	O
the	O
methods	B-Language
defined	O
by	O
superclasses	O
.	O
</s>
<s>
Multiple	B-Application
inheritance	I-Application
is	O
allowed	O
in	O
some	O
languages	O
,	O
though	O
this	O
can	O
make	O
resolving	O
overrides	O
complicated	O
.	O
</s>
<s>
Some	O
languages	O
have	O
special	O
support	O
for	O
mixins	B-Language
,	O
though	O
in	O
any	O
language	O
with	O
multiple	B-Application
inheritance	I-Application
,	O
a	O
mixin	B-Language
is	O
simply	O
a	O
class	O
that	O
does	O
not	O
represent	O
an	O
is-a-type-of	O
relationship	O
.	O
</s>
<s>
Mixins	B-Language
are	O
typically	O
used	O
to	O
add	O
the	O
same	O
methods	B-Language
to	O
multiple	O
classes	B-Application
.	O
</s>
<s>
Abstract	O
classes	B-Application
cannot	O
be	O
instantiated	O
into	O
objects	O
;	O
they	O
exist	O
only	O
for	O
the	O
purpose	O
of	O
inheritance	B-Language
into	O
other	O
"	O
concrete	O
"	O
classes	B-Application
that	O
can	O
be	O
instantiated	O
.	O
</s>
<s>
In	O
Java	B-Language
,	O
the	O
final	B-Language
keyword	O
can	O
be	O
used	O
to	O
prevent	O
a	O
class	O
from	O
being	O
subclassed	O
.	O
</s>
<s>
The	O
doctrine	O
of	O
composition	B-Library
over	I-Library
inheritance	I-Library
advocates	O
implementing	O
has-a	O
relationships	O
using	O
composition	O
instead	O
of	O
inheritance	B-Language
.	O
</s>
<s>
For	O
example	O
,	O
instead	O
of	O
inheriting	O
from	O
class	O
Person	O
,	O
class	O
Employee	O
could	O
give	O
each	O
Employee	O
object	B-Device
an	O
internal	O
Person	O
object	B-Device
,	O
which	O
it	O
then	O
has	O
the	O
opportunity	O
to	O
hide	O
from	O
external	O
code	B-Application
even	O
if	O
class	O
Person	O
has	O
many	O
public	O
attributes	B-General_Concept
or	O
methods	B-Language
.	O
</s>
<s>
Some	O
languages	O
,	O
like	O
Go	B-Application
do	O
not	O
support	O
inheritance	B-Language
at	O
all	O
.	O
</s>
<s>
The	O
"	O
open/closed	O
principle	O
"	O
advocates	O
that	O
classes	B-Application
and	O
functions	B-Language
"	O
should	O
be	O
open	O
for	O
extension	O
,	O
but	O
closed	O
for	O
modification	O
"	O
.	O
</s>
<s>
Delegation	B-Application
is	O
another	O
language	O
feature	O
that	O
can	O
be	O
used	O
as	O
an	O
alternative	O
to	O
inheritance	B-Language
.	O
</s>
<s>
Subtyping	O
–	O
a	O
form	O
of	O
polymorphism	B-Application
–	O
is	O
when	O
calling	O
code	B-Application
can	O
be	O
independent	O
of	O
which	O
class	O
in	O
the	O
supported	O
hierarchy	O
it	O
is	O
operating	O
on	O
–	O
the	O
parent	O
class	O
or	O
one	O
of	O
its	O
descendants	O
.	O
</s>
<s>
Meanwhile	O
,	O
the	O
same	O
operation	O
name	O
among	O
objects	O
in	O
an	O
inheritance	B-Language
hierarchy	I-Language
may	O
behave	O
differently	O
.	O
</s>
<s>
The	O
Draw	O
function	O
for	O
each	O
type	O
of	O
Shape	O
implements	O
what	O
is	O
necessary	O
to	O
draw	O
itself	O
while	O
calling	O
code	B-Application
can	O
remain	O
indifferent	O
to	O
the	O
particular	O
type	O
of	O
Shape	O
being	O
drawn	O
.	O
</s>
<s>
This	O
is	O
another	O
type	O
of	O
abstraction	B-Application
that	O
simplifies	O
code	B-Application
external	O
to	O
the	O
class	O
hierarchy	O
and	O
enables	O
strong	O
separation	O
of	O
concerns	O
.	O
</s>
<s>
In	O
languages	O
that	O
support	O
open	B-Algorithm
recursion	I-Algorithm
,	O
object	B-Device
methods	B-Language
can	O
call	O
other	O
methods	B-Language
on	O
the	O
same	O
object	B-Device
(	O
including	O
themselves	O
)	O
,	O
typically	O
using	O
a	O
special	O
variable	O
or	O
keyword	O
called	O
this	O
or	O
self	B-Operating_System
.	O
</s>
<s>
Simula	B-Language
(	O
1967	O
)	O
is	O
generally	O
accepted	O
as	O
being	O
the	O
first	O
language	O
with	O
the	O
primary	O
features	O
of	O
an	O
object-oriented	B-Language
language	I-Language
.	O
</s>
<s>
It	O
was	O
created	O
for	O
making	O
simulation	B-Application
programs	I-Application
,	O
in	O
which	O
what	O
came	O
to	O
be	O
called	O
objects	O
were	O
the	O
most	O
important	O
information	O
representation	O
.	O
</s>
<s>
Smalltalk	B-Application
(	O
1972	O
to	O
1980	O
)	O
is	O
another	O
early	O
example	O
,	O
and	O
the	O
one	O
with	O
which	O
much	O
of	O
the	O
theory	O
of	O
OOP	O
was	O
developed	O
.	O
</s>
<s>
Concerning	O
the	O
degree	O
of	O
object	B-Device
orientation	O
,	O
the	O
following	O
distinctions	O
can	O
be	O
made	O
:	O
</s>
<s>
Languages	O
called	O
"	O
pure	O
"	O
OO	O
languages	O
,	O
because	O
everything	O
in	O
them	O
is	O
treated	O
consistently	O
as	O
an	O
object	B-Device
,	O
from	O
primitives	O
such	O
as	O
characters	O
and	O
punctuation	O
,	O
all	O
the	O
way	O
up	O
to	O
whole	O
classes	B-Application
,	O
prototypes	B-Application
,	O
blocks	O
,	O
modules	B-Architecture
,	O
etc	O
.	O
</s>
<s>
They	O
were	O
designed	O
specifically	O
to	O
facilitate	O
,	O
even	O
enforce	O
,	O
OO	O
methods	B-Language
.	O
</s>
<s>
Examples	O
:	O
Ruby	B-Language
,	O
Scala	B-Application
,	O
Smalltalk	B-Application
,	O
Eiffel	B-Language
,	O
Emerald	B-Language
,	O
JADE	B-Language
,	O
Self	B-Operating_System
,	O
Raku	B-Application
.	O
</s>
<s>
Languages	O
designed	O
mainly	O
for	O
OO	O
programming	O
,	O
but	O
with	O
some	O
procedural	B-Application
elements	O
.	O
</s>
<s>
Examples	O
:	O
Java	B-Language
,	O
Python	B-Language
,	O
C++	B-Language
,	O
C#	B-Application
,	O
Delphi/Object	O
Pascal	O
,	O
VB.NET	B-Language
.	O
</s>
<s>
Languages	O
that	O
are	O
historically	O
procedural	B-Application
languages	I-Application
,	O
but	O
have	O
been	O
extended	O
with	O
some	O
OO	O
features	O
.	O
</s>
<s>
Examples	O
:	O
PHP	B-Application
,	O
JavaScript	B-Language
,	O
Perl	B-Language
,	O
Visual	B-Language
Basic	I-Language
(	O
derived	O
from	O
BASIC	O
)	O
,	O
MATLAB	B-Language
,	O
COBOL	B-Language
2002	I-Language
,	O
Fortran	B-Application
2003	I-Application
,	O
ABAP	B-Language
,	O
Ada	B-Language
95	I-Language
,	O
Pascal	B-Application
.	O
</s>
<s>
Languages	O
with	O
most	O
of	O
the	O
features	O
of	O
objects	O
(	O
classes	B-Application
,	O
methods	B-Language
,	O
inheritance	B-Language
)	O
,	O
but	O
in	O
a	O
distinctly	O
original	O
form	O
.	O
</s>
<s>
Examples	O
:	O
Oberon	B-Language
(	O
Oberon-1	B-Language
or	O
Oberon-2	O
)	O
.	O
</s>
<s>
Languages	O
with	O
abstract	O
data	O
type	O
support	O
which	O
may	O
be	O
used	O
to	O
resemble	O
OO	O
programming	O
,	O
but	O
without	O
all	O
features	O
of	O
object-orientation	O
.	O
</s>
<s>
This	O
includes	O
object-based	B-Application
and	O
prototype-based	B-Application
languages	I-Application
.	O
</s>
<s>
Examples	O
:	O
JavaScript	B-Language
,	O
Lua	B-Language
,	O
Modula-2	B-Language
,	O
CLU	B-Language
.	O
</s>
<s>
Tcl	B-Operating_System
stands	O
out	O
among	O
these	O
for	O
TclOO	O
,	O
a	O
hybrid	O
object	B-Language
system	I-Language
that	O
supports	O
both	O
prototype-based	B-Application
programming	I-Application
and	O
class-based	B-Application
OO	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
object-oriented	B-Language
programming	I-Language
has	O
become	O
especially	O
popular	O
in	O
dynamic	B-Language
programming	I-Language
languages	I-Language
.	O
</s>
<s>
Python	B-Language
,	O
PowerShell	B-Application
,	O
Ruby	B-Language
and	O
Groovy	B-Application
are	O
dynamic	B-Language
languages	I-Language
built	O
on	O
OOP	O
principles	O
,	O
while	O
Perl	B-Language
and	O
PHP	B-Application
have	O
been	O
adding	O
object-oriented	B-Language
features	O
since	O
Perl	B-Language
5	O
and	O
PHP	B-Application
4	O
,	O
and	O
ColdFusion	B-Language
since	O
version	O
6	O
.	O
</s>
<s>
The	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
of	O
HTML	B-Language
,	O
XHTML	B-Language
,	O
and	O
XML	B-Protocol
documents	I-Protocol
on	O
the	O
Internet	O
has	O
bindings	O
to	O
the	O
popular	O
JavaScript/ECMAScript	O
language	O
.	O
</s>
<s>
JavaScript	B-Language
is	O
perhaps	O
the	O
best	O
known	O
prototype-based	B-Application
programming	I-Application
language	I-Application
,	O
which	O
employs	O
cloning	O
from	O
prototypes	B-Application
rather	O
than	O
inheriting	O
from	O
a	O
class	O
(	O
contrast	O
to	O
class-based	B-Application
programming	I-Application
)	O
.	O
</s>
<s>
Another	O
scripting	O
language	O
that	O
takes	O
this	O
approach	O
is	O
Lua	B-Language
.	O
</s>
<s>
For	O
example	O
,	O
a	O
simple	O
linearized	O
object	B-Device
would	O
consist	O
of	O
a	O
length	O
field	O
,	O
a	O
code	B-Application
point	O
identifying	O
the	O
class	O
,	O
and	O
a	O
data	O
value	O
.	O
</s>
<s>
A	O
more	O
complex	O
example	O
would	O
be	O
a	O
command	O
consisting	O
of	O
the	O
length	O
and	O
code	B-Application
point	O
of	O
the	O
command	O
and	O
values	O
consisting	O
of	O
linearized	O
objects	O
representing	O
the	O
command	O
's	O
parameters	O
.	O
</s>
<s>
Each	O
such	O
command	O
must	O
be	O
directed	O
by	O
the	O
server	O
to	O
an	O
object	B-Device
whose	O
class	O
(	O
or	O
superclass	O
)	O
recognizes	O
the	O
command	O
and	O
is	O
able	O
to	O
provide	O
the	O
requested	O
service	O
.	O
</s>
<s>
Clients	O
and	O
servers	O
are	O
best	O
modeled	O
as	O
complex	O
object-oriented	B-Language
structures	O
.	O
</s>
<s>
Distributed	B-Operating_System
Data	I-Operating_System
Management	I-Operating_System
Architecture	I-Operating_System
(	O
DDM	O
)	O
took	O
this	O
approach	O
and	O
used	O
class	O
objects	O
to	O
define	O
objects	O
at	O
four	O
levels	O
of	O
a	O
formal	O
hierarchy	O
:	O
</s>
<s>
Fields	B-Application
defining	O
the	O
data	O
values	O
that	O
form	O
messages	O
,	O
such	O
as	O
their	O
length	O
,	O
code	B-Application
point	O
and	O
data	O
values	O
.	O
</s>
<s>
Objects	O
and	O
collections	O
of	O
objects	O
similar	O
to	O
what	O
would	O
be	O
found	O
in	O
a	O
Smalltalk	B-Application
program	O
for	O
messages	O
and	O
parameters	O
.	O
</s>
<s>
Managers	O
similar	O
to	O
IBM	B-Application
i	I-Application
Objects	O
,	O
such	O
as	O
a	O
directory	O
to	O
files	O
and	O
files	O
consisting	O
of	O
metadata	O
and	O
records	O
.	O
</s>
<s>
It	O
was	O
later	O
extended	O
to	O
be	O
the	O
foundation	O
of	O
Distributed	B-Language
Relational	I-Language
Database	I-Language
Architecture	I-Language
(	O
DRDA	B-Language
)	O
.	O
</s>
<s>
Challenges	O
of	O
object-oriented	B-Language
design	O
are	O
addressed	O
by	O
several	O
approaches	O
.	O
</s>
<s>
Some	O
of	O
these	O
commonly	O
occurring	O
problems	O
have	O
implications	O
and	O
solutions	O
particular	O
to	O
object-oriented	B-Language
development	O
.	O
</s>
<s>
It	O
is	O
intuitive	O
to	O
assume	O
that	O
inheritance	B-Language
creates	O
a	O
semantic	B-Application
"	O
is	O
a	O
"	O
relationship	O
,	O
and	O
thus	O
to	O
infer	O
that	O
objects	O
instantiated	O
from	O
subclasses	O
can	O
always	O
be	O
safely	O
used	O
instead	O
of	O
those	O
instantiated	O
from	O
the	O
superclass	O
.	O
</s>
<s>
This	O
intuition	O
is	O
unfortunately	O
false	O
in	O
most	O
OOP	O
languages	O
,	O
in	O
particular	O
in	O
all	O
those	O
that	O
allow	O
mutable	B-Application
objects	I-Application
.	O
</s>
<s>
Subtype	O
polymorphism	B-Application
as	O
enforced	O
by	O
the	O
type	O
checker	O
in	O
OOP	O
languages	O
(	O
with	O
mutable	B-Application
objects	I-Application
)	O
cannot	O
guarantee	O
behavioral	B-Application
subtyping	I-Application
in	O
any	O
context	O
.	O
</s>
<s>
Behavioral	B-Application
subtyping	I-Application
is	O
undecidable	O
in	O
general	O
,	O
so	O
it	O
cannot	O
be	O
implemented	O
by	O
a	O
program	O
(	O
compiler	B-Language
)	O
.	O
</s>
<s>
Class	O
or	O
object	B-Device
hierarchies	O
must	O
be	O
carefully	O
designed	O
,	O
considering	O
possible	O
incorrect	O
uses	O
that	O
cannot	O
be	O
detected	O
syntactically	O
.	O
</s>
<s>
This	O
issue	O
is	O
known	O
as	O
the	O
Liskov	B-Application
substitution	I-Application
principle	I-Application
.	O
</s>
<s>
Design	O
Patterns	O
:	O
Elements	O
of	O
Reusable	O
Object-Oriented	B-Language
Software	O
is	O
an	O
influential	O
book	O
published	O
in	O
1994	O
by	O
Erich	O
Gamma	O
,	O
Richard	O
Helm	O
,	O
Ralph	O
Johnson	O
,	O
and	O
John	O
Vlissides	O
,	O
often	O
referred	O
to	O
humorously	O
as	O
the	O
"	O
Gang	O
of	O
Four	O
"	O
.	O
</s>
<s>
Along	O
with	O
exploring	O
the	O
capabilities	O
and	O
pitfalls	O
of	O
object-oriented	B-Language
programming	I-Language
,	O
it	O
describes	O
23	O
common	O
programming	O
problems	O
and	O
patterns	O
for	O
solving	O
them	O
.	O
</s>
<s>
Both	O
object-oriented	B-Language
programming	I-Language
and	O
relational	B-Application
database	I-Application
management	I-Application
systems	I-Application
(	O
RDBMSs	O
)	O
are	O
extremely	O
common	O
in	O
software	O
.	O
</s>
<s>
Since	O
relational	B-Application
databases	I-Application
do	O
n't	O
store	O
objects	O
directly	O
(	O
though	O
some	O
RDBMSs	O
have	O
object-oriented	B-Language
features	O
to	O
approximate	O
this	O
)	O
,	O
there	O
is	O
a	O
general	O
need	O
to	O
bridge	O
the	O
two	O
worlds	O
.	O
</s>
<s>
The	O
problem	O
of	O
bridging	O
object-oriented	B-Language
programming	I-Language
accesses	O
and	O
data	O
patterns	O
with	O
relational	B-Application
databases	I-Application
is	O
known	O
as	O
object-relational	B-Architecture
impedance	I-Architecture
mismatch	I-Architecture
.	O
</s>
<s>
One	O
of	O
the	O
most	O
common	O
approaches	O
is	O
object-relational	B-General_Concept
mapping	I-General_Concept
,	O
as	O
found	O
in	O
IDE	B-Application
languages	O
such	O
as	O
Visual	B-Application
FoxPro	I-Application
and	O
libraries	O
such	O
as	O
Java	B-Language
Data	I-Language
Objects	I-Language
and	O
Ruby	B-Application
on	I-Application
Rails	I-Application
 '	O
ActiveRecord	O
.	O
</s>
<s>
There	O
are	O
also	O
object	B-Application
databases	I-Application
that	O
can	O
be	O
used	O
to	O
replace	O
RDBMSs	O
,	O
but	O
these	O
have	O
not	O
been	O
as	O
technically	O
and	O
commercially	O
successful	O
as	O
RDBMSs	O
.	O
</s>
<s>
However	O
,	O
not	O
everyone	O
agrees	O
that	O
OOP	O
facilitates	O
direct	O
real-world	O
mapping	O
(	O
see	O
Criticism	O
section	O
)	O
or	O
that	O
real-world	O
mapping	O
is	O
even	O
a	O
worthy	O
goal	O
;	O
Bertrand	O
Meyer	O
argues	O
in	O
Object-Oriented	B-Language
Software	O
Construction	O
that	O
a	O
program	O
is	O
not	O
a	O
model	O
of	O
the	O
world	O
but	O
a	O
model	O
of	O
some	O
part	O
of	O
the	O
world	O
;	O
"	O
Reality	O
is	O
a	O
cousin	O
twice	O
removed	O
"	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
circle-ellipse	B-Application
problem	I-Application
is	O
difficult	O
to	O
handle	O
using	O
OOP	O
's	O
concept	O
of	O
inheritance	B-Language
.	O
</s>
<s>
Steve	O
Yegge	O
and	O
others	O
noted	O
that	O
natural	O
languages	O
lack	O
the	O
OOP	O
approach	O
of	O
strictly	O
prioritizing	O
things	O
(	O
objects/nouns	O
)	O
before	O
actions	O
(	O
methods/verbs	O
)	O
.	O
</s>
<s>
This	O
problem	O
may	O
cause	O
OOP	O
to	O
suffer	O
more	O
convoluted	O
solutions	O
than	O
procedural	B-Application
programming	I-Application
.	O
</s>
<s>
OOP	O
was	O
developed	O
to	O
increase	O
the	O
reusability	O
and	O
maintainability	O
of	O
source	O
code	B-Application
.	O
</s>
<s>
Transparent	O
representation	O
of	O
the	O
control	O
flow	O
had	O
no	O
priority	O
and	O
was	O
meant	O
to	O
be	O
handled	O
by	O
a	O
compiler	B-Language
.	O
</s>
<s>
With	O
the	O
increasing	O
relevance	O
of	O
parallel	O
hardware	O
and	O
multithreaded	B-Operating_System
coding	I-Operating_System
,	O
developing	O
transparent	O
control	O
flow	O
becomes	O
more	O
important	O
,	O
something	O
hard	O
to	O
achieve	O
with	O
OOP	O
.	O
</s>
<s>
Responsibility-driven	B-Application
design	I-Application
defines	O
classes	B-Application
in	O
terms	O
of	O
a	O
contract	O
,	O
that	O
is	O
,	O
a	O
class	O
should	O
be	O
defined	O
around	O
a	O
responsibility	O
and	O
the	O
information	O
that	O
it	O
shares	O
.	O
</s>
<s>
This	O
is	O
contrasted	O
by	O
Wirfs-Brock	O
and	O
Wilkerson	O
with	O
data-driven	B-Application
design	I-Application
,	O
where	O
classes	B-Application
are	O
defined	O
around	O
the	O
data-structures	O
that	O
must	O
be	O
held	O
.	O
</s>
<s>
The	O
authors	O
hold	O
that	O
responsibility-driven	B-Application
design	I-Application
is	O
preferable	O
.	O
</s>
<s>
The	O
OOP	O
paradigm	O
has	O
been	O
criticised	O
for	O
a	O
number	O
of	O
reasons	O
,	O
including	O
not	O
meeting	O
its	O
stated	O
goals	O
of	O
reusability	O
and	O
modularity	B-Architecture
,	O
and	O
for	O
overemphasizing	O
one	O
aspect	O
of	O
software	O
design	O
and	O
modeling	O
(	O
data/objects	O
)	O
at	O
the	O
expense	O
of	O
other	O
important	O
aspects	O
(	O
computation/algorithms	O
)	O
.	O
</s>
<s>
Luca	O
Cardelli	O
has	O
claimed	O
that	O
OOP	O
code	B-Application
is	O
"	O
intrinsically	O
less	O
efficient	O
"	O
than	O
procedural	B-Application
code	I-Application
,	O
that	O
OOP	O
can	O
take	O
longer	O
to	O
compile	B-Language
,	O
and	O
that	O
OOP	O
languages	O
have	O
"	O
extremely	O
poor	O
modularity	B-Architecture
properties	O
with	O
respect	O
to	O
class	O
extension	O
and	O
modification	O
"	O
,	O
and	O
tend	O
to	O
be	O
extremely	O
complex	O
.	O
</s>
<s>
The	O
latter	O
point	O
is	O
reiterated	O
by	O
Joe	O
Armstrong	O
,	O
the	O
principal	O
inventor	O
of	O
Erlang	B-Operating_System
,	O
who	O
is	O
quoted	O
as	O
saying	O
:	O
</s>
<s>
has	O
shown	O
no	O
significant	O
difference	O
in	O
productivity	O
between	O
OOP	O
and	O
procedural	B-Application
approaches	O
.	O
</s>
<s>
In	O
an	O
article	O
Lawrence	O
Krubner	O
claimed	O
that	O
compared	O
to	O
other	O
languages	O
(	O
LISP	B-Language
dialects	O
,	O
functional	B-Language
languages	I-Language
,	O
etc	O
.	O
)	O
</s>
<s>
Alexander	O
Stepanov	O
compares	O
object	B-Device
orientation	O
unfavourably	O
to	O
generic	B-Language
programming	I-Language
:	O
</s>
<s>
Leo	O
Brodie	O
has	O
suggested	O
a	O
connection	O
between	O
the	O
standalone	O
nature	O
of	O
objects	O
and	O
a	O
tendency	O
to	O
duplicate	O
code	B-Application
in	O
violation	O
of	O
the	O
do	O
n't	O
repeat	O
yourself	O
principle	O
of	O
software	O
development	O
.	O
</s>
<s>
Steve	O
Yegge	O
noted	O
that	O
,	O
as	O
opposed	O
to	O
functional	B-Language
programming	I-Language
:	O
</s>
<s>
Rich	O
Hickey	O
,	O
creator	O
of	O
Clojure	B-Language
,	O
described	O
object	B-Language
systems	I-Language
as	O
overly	O
simplistic	O
models	O
of	O
the	O
real	O
world	O
.	O
</s>
<s>
Eric	O
S	O
.	O
Raymond	O
,	O
a	O
Unix	B-Application
programmer	O
and	O
open-source	B-Application
software	I-Application
advocate	O
,	O
has	O
been	O
critical	O
of	O
claims	O
that	O
present	O
object-oriented	B-Language
programming	I-Language
as	O
the	O
"	O
One	O
True	O
Solution	O
"	O
,	O
and	O
has	O
written	O
that	O
object-oriented	B-Language
programming	I-Language
languages	I-Language
tend	O
to	O
encourage	O
thickly	O
layered	O
programs	O
that	O
destroy	O
transparency	O
.	O
</s>
<s>
Raymond	O
compares	O
this	O
unfavourably	O
to	O
the	O
approach	O
taken	O
with	O
Unix	B-Application
and	O
the	O
C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Rob	O
Pike	O
,	O
a	O
programmer	O
involved	O
in	O
the	O
creation	O
of	O
UTF-8	O
and	O
Go	B-Application
,	O
has	O
called	O
object-oriented	B-Language
programming	I-Language
"	O
the	O
Roman	O
numerals	O
of	O
computing	O
"	O
and	O
has	O
said	O
that	O
OOP	O
languages	O
frequently	O
shift	O
the	O
focus	O
from	O
data	B-General_Concept
structures	I-General_Concept
and	O
algorithms	O
to	O
types	O
.	O
</s>
<s>
Furthermore	O
,	O
he	O
cites	O
an	O
instance	O
of	O
a	O
Java	B-Language
professor	O
whose	O
"	O
idiomatic	O
"	O
solution	O
to	O
a	O
problem	O
was	O
to	O
create	O
six	O
new	O
classes	B-Application
,	O
rather	O
than	O
to	O
simply	O
use	O
a	O
lookup	B-Data_Structure
table	I-Data_Structure
.	O
</s>
<s>
Regarding	O
inheritance	B-Language
,	O
Bob	O
Martin	O
states	O
that	O
because	O
they	O
are	O
software	O
,	O
related	O
classes	B-Application
do	O
not	O
necessarily	O
share	O
the	O
relationships	O
of	O
the	O
things	O
they	O
represent	O
.	O
</s>
<s>
Objects	O
are	O
the	O
run-time	O
entities	O
in	O
an	O
object-oriented	B-Language
system	O
.	O
</s>
<s>
There	O
have	O
been	O
several	O
attempts	O
at	O
formalizing	O
the	O
concepts	O
used	O
in	O
object-oriented	B-Language
programming	I-Language
.	O
</s>
<s>
records	O
are	O
basis	O
for	O
understanding	O
objects	O
if	O
function	B-General_Concept
literals	I-General_Concept
can	O
be	O
stored	O
in	O
fields	B-Application
(	O
like	O
in	O
functional-programming	O
languages	O
)	O
,	O
but	O
the	O
actual	O
calculi	O
need	O
be	O
considerably	O
more	O
complex	O
to	O
incorporate	O
essential	O
features	O
of	O
OOP	O
.	O
</s>
<s>
One	O
of	O
the	O
simpler	O
definitions	O
is	O
that	O
OOP	O
is	O
the	O
act	O
of	O
using	O
"	O
map	O
"	O
data	B-General_Concept
structures	I-General_Concept
or	O
arrays	O
that	O
can	O
contain	O
functions	B-Language
and	O
pointers	O
to	O
other	O
maps	O
,	O
all	O
with	O
some	O
syntactic	O
and	O
scoping	O
sugar	O
on	O
top	O
.	O
</s>
<s>
Inheritance	B-Language
can	O
be	O
performed	O
by	O
cloning	O
the	O
maps	O
(	O
sometimes	O
called	O
"	O
prototyping	O
"	O
)	O
.	O
</s>
