408 lines
15 KiB
HTML
Executable File
408 lines
15 KiB
HTML
Executable File
<?xml version="1.0" encoding="utf-8"?>
|
||
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
|
||
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
||
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
|
||
<head>
|
||
<!-- 2025-12-28 Sun 20:49 -->
|
||
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
|
||
<meta name="viewport" content="width=device-width, initial-scale=1" />
|
||
<title>Design patterns</title>
|
||
<meta name="generator" content="Org Mode" />
|
||
<style type="text/css">
|
||
#content { max-width: 60em; margin: auto; }
|
||
.title { text-align: center;
|
||
margin-bottom: .2em; }
|
||
.subtitle { text-align: center;
|
||
font-size: medium;
|
||
font-weight: bold;
|
||
margin-top:0; }
|
||
.todo { font-family: monospace; color: red; }
|
||
.done { font-family: monospace; color: green; }
|
||
.priority { font-family: monospace; color: orange; }
|
||
.tag { background-color: #eee; font-family: monospace;
|
||
padding: 2px; font-size: 80%; font-weight: normal; }
|
||
.timestamp { color: #bebebe; }
|
||
.timestamp-kwd { color: #5f9ea0; }
|
||
.org-right { margin-left: auto; margin-right: 0px; text-align: right; }
|
||
.org-left { margin-left: 0px; margin-right: auto; text-align: left; }
|
||
.org-center { margin-left: auto; margin-right: auto; text-align: center; }
|
||
.underline { text-decoration: underline; }
|
||
#postamble p, #preamble p { font-size: 90%; margin: .2em; }
|
||
p.verse { margin-left: 3%; }
|
||
pre {
|
||
border: 1px solid #e6e6e6;
|
||
border-radius: 3px;
|
||
background-color: #f2f2f2;
|
||
padding: 8pt;
|
||
font-family: monospace;
|
||
overflow: auto;
|
||
margin: 1.2em;
|
||
}
|
||
pre.src {
|
||
position: relative;
|
||
overflow: auto;
|
||
}
|
||
pre.src:before {
|
||
display: none;
|
||
position: absolute;
|
||
top: -8px;
|
||
right: 12px;
|
||
padding: 3px;
|
||
color: #555;
|
||
background-color: #f2f2f299;
|
||
}
|
||
pre.src:hover:before { display: inline; margin-top: 14px;}
|
||
/* Languages per Org manual */
|
||
pre.src-asymptote:before { content: 'Asymptote'; }
|
||
pre.src-awk:before { content: 'Awk'; }
|
||
pre.src-authinfo::before { content: 'Authinfo'; }
|
||
pre.src-C:before { content: 'C'; }
|
||
/* pre.src-C++ doesn't work in CSS */
|
||
pre.src-clojure:before { content: 'Clojure'; }
|
||
pre.src-css:before { content: 'CSS'; }
|
||
pre.src-D:before { content: 'D'; }
|
||
pre.src-ditaa:before { content: 'ditaa'; }
|
||
pre.src-dot:before { content: 'Graphviz'; }
|
||
pre.src-calc:before { content: 'Emacs Calc'; }
|
||
pre.src-emacs-lisp:before { content: 'Emacs Lisp'; }
|
||
pre.src-fortran:before { content: 'Fortran'; }
|
||
pre.src-gnuplot:before { content: 'gnuplot'; }
|
||
pre.src-haskell:before { content: 'Haskell'; }
|
||
pre.src-hledger:before { content: 'hledger'; }
|
||
pre.src-java:before { content: 'Java'; }
|
||
pre.src-js:before { content: 'Javascript'; }
|
||
pre.src-latex:before { content: 'LaTeX'; }
|
||
pre.src-ledger:before { content: 'Ledger'; }
|
||
pre.src-lisp:before { content: 'Lisp'; }
|
||
pre.src-lilypond:before { content: 'Lilypond'; }
|
||
pre.src-lua:before { content: 'Lua'; }
|
||
pre.src-matlab:before { content: 'MATLAB'; }
|
||
pre.src-mscgen:before { content: 'Mscgen'; }
|
||
pre.src-ocaml:before { content: 'Objective Caml'; }
|
||
pre.src-octave:before { content: 'Octave'; }
|
||
pre.src-org:before { content: 'Org mode'; }
|
||
pre.src-oz:before { content: 'OZ'; }
|
||
pre.src-plantuml:before { content: 'Plantuml'; }
|
||
pre.src-processing:before { content: 'Processing.js'; }
|
||
pre.src-python:before { content: 'Python'; }
|
||
pre.src-R:before { content: 'R'; }
|
||
pre.src-ruby:before { content: 'Ruby'; }
|
||
pre.src-sass:before { content: 'Sass'; }
|
||
pre.src-scheme:before { content: 'Scheme'; }
|
||
pre.src-screen:before { content: 'Gnu Screen'; }
|
||
pre.src-sed:before { content: 'Sed'; }
|
||
pre.src-sh:before { content: 'shell'; }
|
||
pre.src-sql:before { content: 'SQL'; }
|
||
pre.src-sqlite:before { content: 'SQLite'; }
|
||
/* additional languages in org.el's org-babel-load-languages alist */
|
||
pre.src-forth:before { content: 'Forth'; }
|
||
pre.src-io:before { content: 'IO'; }
|
||
pre.src-J:before { content: 'J'; }
|
||
pre.src-makefile:before { content: 'Makefile'; }
|
||
pre.src-maxima:before { content: 'Maxima'; }
|
||
pre.src-perl:before { content: 'Perl'; }
|
||
pre.src-picolisp:before { content: 'Pico Lisp'; }
|
||
pre.src-scala:before { content: 'Scala'; }
|
||
pre.src-shell:before { content: 'Shell Script'; }
|
||
pre.src-ebnf2ps:before { content: 'ebfn2ps'; }
|
||
/* additional language identifiers per "defun org-babel-execute"
|
||
in ob-*.el */
|
||
pre.src-cpp:before { content: 'C++'; }
|
||
pre.src-abc:before { content: 'ABC'; }
|
||
pre.src-coq:before { content: 'Coq'; }
|
||
pre.src-groovy:before { content: 'Groovy'; }
|
||
/* additional language identifiers from org-babel-shell-names in
|
||
ob-shell.el: ob-shell is the only babel language using a lambda to put
|
||
the execution function name together. */
|
||
pre.src-bash:before { content: 'bash'; }
|
||
pre.src-csh:before { content: 'csh'; }
|
||
pre.src-ash:before { content: 'ash'; }
|
||
pre.src-dash:before { content: 'dash'; }
|
||
pre.src-ksh:before { content: 'ksh'; }
|
||
pre.src-mksh:before { content: 'mksh'; }
|
||
pre.src-posh:before { content: 'posh'; }
|
||
/* Additional Emacs modes also supported by the LaTeX listings package */
|
||
pre.src-ada:before { content: 'Ada'; }
|
||
pre.src-asm:before { content: 'Assembler'; }
|
||
pre.src-caml:before { content: 'Caml'; }
|
||
pre.src-delphi:before { content: 'Delphi'; }
|
||
pre.src-html:before { content: 'HTML'; }
|
||
pre.src-idl:before { content: 'IDL'; }
|
||
pre.src-mercury:before { content: 'Mercury'; }
|
||
pre.src-metapost:before { content: 'MetaPost'; }
|
||
pre.src-modula-2:before { content: 'Modula-2'; }
|
||
pre.src-pascal:before { content: 'Pascal'; }
|
||
pre.src-ps:before { content: 'PostScript'; }
|
||
pre.src-prolog:before { content: 'Prolog'; }
|
||
pre.src-simula:before { content: 'Simula'; }
|
||
pre.src-tcl:before { content: 'tcl'; }
|
||
pre.src-tex:before { content: 'TeX'; }
|
||
pre.src-plain-tex:before { content: 'Plain TeX'; }
|
||
pre.src-verilog:before { content: 'Verilog'; }
|
||
pre.src-vhdl:before { content: 'VHDL'; }
|
||
pre.src-xml:before { content: 'XML'; }
|
||
pre.src-nxml:before { content: 'XML'; }
|
||
/* add a generic configuration mode; LaTeX export needs an additional
|
||
(add-to-list 'org-latex-listings-langs '(conf " ")) in .emacs */
|
||
pre.src-conf:before { content: 'Configuration File'; }
|
||
|
||
table { border-collapse:collapse; }
|
||
caption.t-above { caption-side: top; }
|
||
caption.t-bottom { caption-side: bottom; }
|
||
td, th { vertical-align:top; }
|
||
th.org-right { text-align: center; }
|
||
th.org-left { text-align: center; }
|
||
th.org-center { text-align: center; }
|
||
td.org-right { text-align: right; }
|
||
td.org-left { text-align: left; }
|
||
td.org-center { text-align: center; }
|
||
dt { font-weight: bold; }
|
||
.footpara { display: inline; }
|
||
.footdef { margin-bottom: 1em; }
|
||
.figure { padding: 1em; }
|
||
.figure p { text-align: center; }
|
||
.equation-container {
|
||
display: table;
|
||
text-align: center;
|
||
width: 100%;
|
||
}
|
||
.equation {
|
||
vertical-align: middle;
|
||
}
|
||
.equation-label {
|
||
display: table-cell;
|
||
text-align: right;
|
||
vertical-align: middle;
|
||
}
|
||
.inlinetask {
|
||
padding: 10px;
|
||
border: 2px solid gray;
|
||
margin: 10px;
|
||
background: #ffffcc;
|
||
}
|
||
#org-div-home-and-up
|
||
{ text-align: right; font-size: 70%; white-space: nowrap; }
|
||
textarea { overflow-x: auto; }
|
||
.linenr { font-size: smaller }
|
||
.code-highlighted { background-color: #ffff00; }
|
||
.org-info-js_info-navigation { border-style: none; }
|
||
#org-info-js_console-label
|
||
{ font-size: 10px; font-weight: bold; white-space: nowrap; }
|
||
.org-info-js_search-highlight
|
||
{ background-color: #ffff00; color: #000000; font-weight: bold; }
|
||
.org-svg { }
|
||
</style>
|
||
|
||
<link rel="stylesheet" href="/assets/styles/style.css" />
|
||
<link rel="stylesheet" href="/assets/styles/bigger-picture.min.css" />
|
||
<link rel="stylesheet" href="/assets/styles/media.css" />
|
||
|
||
<script src="/assets/scripts/script.js" defer></script>
|
||
<script src="/assets/scripts/search.js" defer></script>
|
||
<script src="/assets/scripts/bigger-picture.min.js" defer></script>
|
||
<script src="/assets/scripts/svg-pan-zoom.min.js" defer></script>
|
||
<script src="/assets/scripts/gallery-init.js" defer></script>
|
||
</head>
|
||
<body>
|
||
<div id="preamble" class="status">
|
||
|
||
<div class="banner-header">
|
||
<div class="banner-left">
|
||
<a href="/20241210233721-brain_moc.html"> <img src="/assets/gr.png" alt="Site Logo" class="banner-logo" /> </a>
|
||
<div id="updated">Updated: 2025-12-28 Sun 19:48</div>
|
||
</div>
|
||
|
||
<div class="banner-search">
|
||
<input id="search-box"
|
||
type="search"
|
||
placeholder="Search notes…"
|
||
aria-label="Search notes"
|
||
autocomplete="off" />
|
||
<div id="search-results"></div>
|
||
</div>
|
||
|
||
<button id="close-all">Close All</button>
|
||
</div>
|
||
</div>
|
||
<div id="stack-root">
|
||
<div class="stack-track">
|
||
<article class="stack-pane pane-root" data-url="/20251223215636-design_patterns_notes.html">
|
||
<div id="content" class="content">
|
||
<div class="title-section">
|
||
<div class="title-controls">
|
||
<button class="pane-fullscreen" aria-label="Fullscreen">F</button>
|
||
<button class="pane-edit" aria-label="Edit pane">E</button>
|
||
<button class="pane-close" aria-label="Close pane">×</button>
|
||
</div>
|
||
<h1 class="title">Design patterns</h1>
|
||
<div class="title-metadata">
|
||
<span class="metadata-item">
|
||
<span class="metadata-label">planted:</span>
|
||
<span class="metadata-value">2025-12-23</span>
|
||
</span>
|
||
<span class="metadata-item">
|
||
<span class="metadata-label">last tended to:</span>
|
||
<span class="metadata-value">2025-12-28</span>
|
||
</span>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-org93f35de" class="outline-2">
|
||
<h2 id="org93f35de"><a href="#org93f35de">Design patterns. What are they?</a></h2>
|
||
<div class="outline-text-2" id="text-org93f35de">
|
||
<p>
|
||
They are reusable solutions to common problems in software design. They help to make code more flexible, maintainable, and scalable.
|
||
</p>
|
||
|
||
<p>
|
||
Patterns allow you to say more with less. When you use a pattern in a description, other developers quickly know precisely the design you have in mind.
|
||
</p>
|
||
</div>
|
||
<div id="outline-container-org95ca282" class="outline-3">
|
||
<h3 id="org95ca282"><a href="#org95ca282">OO concepts:</a></h3>
|
||
<div class="outline-text-3" id="text-org95ca282">
|
||
</div>
|
||
<div id="outline-container-org7cf919b" class="outline-4">
|
||
<h4 id="org7cf919b"><a href="#org7cf919b">Abstraction:</a></h4>
|
||
<div class="outline-text-4" id="text-org7cf919b">
|
||
<p>
|
||
Focuses on essential features while hiding unnecessary internal details, allowing developers to work with high‑level concepts instead of implementation complexity.
|
||
</p>
|
||
|
||
<p>
|
||
Example: A Car class exposes start() and stop() methods without revealing how the engine ignition system works.
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-orgfede525" class="outline-4">
|
||
<h4 id="orgfede525"><a href="#orgfede525">Inheritance:</a></h4>
|
||
<div class="outline-text-4" id="text-orgfede525">
|
||
<p>
|
||
Enables one class to derive properties and behaviours from another, promoting code reuse and creating natural parent–child hierarchies.
|
||
</p>
|
||
|
||
<p>
|
||
Example: A Dog class inherits from an Animal class, automatically gaining attributes like age and methods like eat().
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-org9c0c14d" class="outline-4">
|
||
<h4 id="org9c0c14d"><a href="#org9c0c14d">Encapsulation:</a></h4>
|
||
<div class="outline-text-4" id="text-org9c0c14d">
|
||
<p>
|
||
Protects an object’s internal state by restricting direct access to its data and exposing controlled interfaces for interaction.
|
||
</p>
|
||
|
||
<p>
|
||
Example: A BankAccount class keeps its balance private and provides deposit() and withdraw() methods to modify it safely.
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-orgd595df4" class="outline-4">
|
||
<h4 id="orgd595df4"><a href="#orgd595df4">Polymorphism:</a></h4>
|
||
<div class="outline-text-4" id="text-orgd595df4">
|
||
<p>
|
||
Allows different objects to respond to the same interface or method call in their own unique ways, enabling flexible and extensible system design.
|
||
</p>
|
||
|
||
<p>
|
||
Example: Calling makeSound() on an Animal reference triggers bark() for a Dog and meow() for a Cat.
|
||
</p>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-org9e0611e" class="outline-3">
|
||
<h3 id="org9e0611e"><a href="#org9e0611e">OO principles:</a></h3>
|
||
<div class="outline-text-3" id="text-org9e0611e">
|
||
<ul class="org-ul">
|
||
<li>Encapsulate what varies</li>
|
||
|
||
<li>Favor composition over inheritance</li>
|
||
|
||
<li>Program to interfaces, not implementations</li>
|
||
|
||
<li>Strive for loosely coupled designs between objects that interact</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div id="outline-container-org6be45eb" class="outline-3">
|
||
<h3 id="org6be45eb"><a href="#org6be45eb">OO Patterns</a></h3>
|
||
<div class="outline-text-3" id="text-org6be45eb">
|
||
<p>
|
||
You have:
|
||
</p>
|
||
<ul class="org-ul">
|
||
<li><b>behavioural</b> patterns</li>
|
||
<li><b>creational</b> patterns</li>
|
||
<li><b>structural</b> patterns</li>
|
||
</ul>
|
||
</div>
|
||
<div id="outline-container-orgcf0c708" class="outline-4">
|
||
<h4 id="orgcf0c708"><a href="#orgcf0c708">Behavioural patterns</a></h4>
|
||
<div class="outline-text-4" id="text-orgcf0c708">
|
||
</div>
|
||
<ul class="org-ul">
|
||
<li><a id="orgb14bd0d"></a><a href="#orgb14bd0d">Structural:</a><br />
|
||
<div class="outline-text-5" id="text-orgb14bd0d">
|
||
<p>
|
||
The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
|
||
</p>
|
||
</div>
|
||
</li>
|
||
<li><a id="orge0f49c2"></a><a href="#orge0f49c2">Observer:</a><br />
|
||
<div class="outline-text-5" id="text-orge0f49c2">
|
||
<p>
|
||
The Observer Pattern defines a one-to-many dependency between objects so that when
|
||
one object changes state, all of its dependents are notified and updated automatically.
|
||
</p>
|
||
|
||
<p>
|
||
Subjects, or as we also know them, Observables, update Observers using a common
|
||
interface
|
||
</p>
|
||
|
||
<p>
|
||
Observers are loosely coupled in that the Observable knows nothing about them,
|
||
other than that they implement the Observer interface.
|
||
</p>
|
||
|
||
<p>
|
||
You can push or pull data from the Observable when using the pattern (pull is
|
||
considered more “correct”).
|
||
</p>
|
||
|
||
<p>
|
||
Don’t depend on a specific order of notification for your Observers.
|
||
</p>
|
||
|
||
<p>
|
||
Java has several implementations of the Observer Pattern, including the general
|
||
purpose java.util.Observable
|
||
</p>
|
||
|
||
<p class="backlinks-section" id="backlinks">
|
||
Backlinks
|
||
</p>
|
||
<ul class="org-ul backlinks-list">
|
||
<li><a href="20241210001045-technical.html#ID-2f285f04-fcf4-4ade-a1ac-2c50b43d529a">Technical MOC</a></li>
|
||
</ul>
|
||
</div>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
</div></article></div></div>
|
||
<div id="postamble" class="status">
|
||
<footer>
|
||
<div class="copyright-container">
|
||
<div class="copyright">
|
||
Copyright © 2022-2025 Zaine Qayyum. All rights reserved unless otherwise noted.</div></div>
|
||
<div class="generated">
|
||
Created with <a href="https://www.gnu.org/software/emacs/">Emacs</a> 30.2 (<a href="https://orgmode.org">Org</a> mode 9.7.11) on <a href="https://www.archlinux.org/">Arch</a> <a href="https://www.gnu.org">GNU</a>/<a href="https://www.kernel.org/">Linux</a>
|
||
</div>
|
||
</footer>
|
||
</div>
|
||
</body>
|
||
</html>
|