369 lines
13 KiB
HTML
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369 lines
13 KiB
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<body>
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<div id="content" class="content">
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<h1 class="title">design-patterns-notes</h1>
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<div id="table-of-contents" role="doc-toc">
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<h2>Table of Contents</h2>
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<div id="text-table-of-contents" role="doc-toc">
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<ul>
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<li><a href="#org1bb65db">1. Design patterns. What are they?</a>
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<ul>
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<li><a href="#orge09a476">1.1. OO concepts:</a>
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<ul>
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<li><a href="#org8c31d5f">1.1.1. Abstraction:</a></li>
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<li><a href="#orgf31693b">1.1.2. Inheritance:</a></li>
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<li><a href="#orgabea4a6">1.1.3. Encapsulation:</a></li>
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<li><a href="#org33bf2fc">1.1.4. Polymorphism:</a></li>
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</ul>
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</li>
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<li><a href="#orga0e9712">1.2. OO principles:</a></li>
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<li><a href="#org8f57089">1.3. OO Patterns</a>
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<ul>
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<li><a href="#org477711e">1.3.1. Behavioural patterns</a></li>
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</ul>
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</li>
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</ul>
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</li>
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</ul>
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</div>
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</div>
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<div id="outline-container-org1bb65db" class="outline-2">
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<h2 id="org1bb65db"><span class="section-number-2">1.</span> Design patterns. What are they?</h2>
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<div class="outline-text-2" id="text-1">
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<p>
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They are reusable solutions to common problems in software design. They help to make code more flexible, maintainable, and scalable.
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</p>
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<p>
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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.
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</p>
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</div>
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<div id="outline-container-orge09a476" class="outline-3">
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<h3 id="orge09a476"><span class="section-number-3">1.1.</span> OO concepts:</h3>
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<div class="outline-text-3" id="text-1-1">
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</div>
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<div id="outline-container-org8c31d5f" class="outline-4">
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<h4 id="org8c31d5f"><span class="section-number-4">1.1.1.</span> Abstraction:</h4>
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<div class="outline-text-4" id="text-1-1-1">
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<p>
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Focuses on essential features while hiding unnecessary internal details, allowing developers to work with high‑level concepts instead of implementation complexity.
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</p>
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<p>
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Example: A Car class exposes start() and stop() methods without revealing how the engine ignition system works.
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</p>
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</div>
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</div>
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<div id="outline-container-orgf31693b" class="outline-4">
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<h4 id="orgf31693b"><span class="section-number-4">1.1.2.</span> Inheritance:</h4>
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<div class="outline-text-4" id="text-1-1-2">
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<p>
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Enables one class to derive properties and behaviours from another, promoting code reuse and creating natural parent–child hierarchies.
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</p>
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<p>
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Example: A Dog class inherits from an Animal class, automatically gaining attributes like age and methods like eat().
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</p>
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</div>
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</div>
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<div id="outline-container-orgabea4a6" class="outline-4">
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<h4 id="orgabea4a6"><span class="section-number-4">1.1.3.</span> Encapsulation:</h4>
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<div class="outline-text-4" id="text-1-1-3">
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<p>
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Protects an object’s internal state by restricting direct access to its data and exposing controlled interfaces for interaction.
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</p>
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<p>
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Example: A BankAccount class keeps its balance private and provides deposit() and withdraw() methods to modify it safely.
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</p>
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</div>
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</div>
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<div id="outline-container-org33bf2fc" class="outline-4">
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<h4 id="org33bf2fc"><span class="section-number-4">1.1.4.</span> Polymorphism:</h4>
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<div class="outline-text-4" id="text-1-1-4">
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<p>
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Allows different objects to respond to the same interface or method call in their own unique ways, enabling flexible and extensible system design.
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</p>
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<p>
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Example: Calling makeSound() on an Animal reference triggers bark() for a Dog and meow() for a Cat.
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</p>
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</div>
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</div>
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</div>
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<div id="outline-container-orga0e9712" class="outline-3">
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<h3 id="orga0e9712"><span class="section-number-3">1.2.</span> OO principles:</h3>
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<div class="outline-text-3" id="text-1-2">
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<ul class="org-ul">
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<li>Encapsulate what varies</li>
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<li>Favor composition over inheritance</li>
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<li>Program to interfaces, not implementations</li>
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<li>Strive for loosely coupled designs between objects that interact</li>
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</ul>
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</div>
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</div>
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<div id="outline-container-org8f57089" class="outline-3">
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<h3 id="org8f57089"><span class="section-number-3">1.3.</span> OO Patterns</h3>
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<div class="outline-text-3" id="text-1-3">
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<p>
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You have:
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</p>
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<ul class="org-ul">
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<li><b>behavioural</b> patterns</li>
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<li><b>creational</b> patterns</li>
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<li><b>structural</b> patterns</li>
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</ul>
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</div>
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<div id="outline-container-org477711e" class="outline-4">
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<h4 id="org477711e"><span class="section-number-4">1.3.1.</span> Behavioural patterns</h4>
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<div class="outline-text-4" id="text-1-3-1">
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</div>
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<ol class="org-ol">
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<li><a id="org2073a8f"></a>Structural:<br />
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<div class="outline-text-5" id="text-1-3-1-1">
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<p>
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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.
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</p>
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</div>
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</li>
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<li><a id="org99ab840"></a>Observer:<br />
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<div class="outline-text-5" id="text-1-3-1-2">
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<p>
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The Observer Pattern defines a one-to-many dependency between objects so that when
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one object changes state, all of its dependents are notified and updated automatically.
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</p>
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<p>
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Subjects, or as we also know them, Observables, update Observers using a common
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interface
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</p>
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<p>
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Observers are loosely coupled in that the Observable knows nothing about them,
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other than that they implement the Observer interface.
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</p>
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<p>
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You can push or pull data from the Observable when using the pattern (pull is
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considered more “correct”).
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</p>
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<p>
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Don’t depend on a specific order of notification for your Observers.
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</p>
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<p>
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Java has several implementations of the Observer Pattern, including the general
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purpose java.util.Observable
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</p>
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</div>
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</li>
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</ol>
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</div>
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</div>
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</div>
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||
</div>
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||
<div id="postamble" class="status">
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<p class="date">Created: 2025-12-24 Wed 14:03</p>
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||
<p class="validation"><a href="https://validator.w3.org/check?uri=referer">Validate</a></p>
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||
</div>
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</body>
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</html>
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