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Dr. Javier Gonzalez-Sanchez [email protected] www.javiergs.info o ffi ce: 14 -227 CSC 307 Introduction to Software Engineering Lecture 09. Patterns

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Homework Quiz 2

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Previously

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Relationships 4 Association Directed Association Reflexive Association Multiplicity Aggregation Composition Generalization Realization

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Good Code vs Bad Code 5

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Not Everything that Can be … Should be … 6

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Not Everything that Can be … Should be … 7

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Patterns

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De f inition • Design patterns a re solutions to softw a re design problems you f ind a g a in a nd a g a in in re a l-world a pplic a tion development. • P a tterns a re a bout reusable designs a nd inter a ctions between objects. • The 23 G a ng of Four (GoF) patterns a re gener a lly considered the found a tion for a ll other p a tterns (G a mm a , Helm, Johnson, a nd Vlissides). 9

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GoF Patterns 10

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Singleton

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Singleton 12

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Singleton 13 https://github.com/CSC3100/Patterns

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Singleton 14 https://github.com/CSC3100/Patterns

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Warning 15 Do not Abuse of the Singleton You are transforming OOP into Structural Programming!! 🙈

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Homework 16 Reading https://medium.com/javarevisited/design-patterns-101-hello-singleton-2d3f227c7729

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Observer

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Observer 18

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Classroom | Initial Version 19 https://github.com/CSC3100/Patterns

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Student | Initial Version 20 https://github.com/CSC3100/Patterns

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Teacher | Initial Version 21 https://github.com/CSC3100/Patterns

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Observer 22

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Observer 23 https://github.com/CSC3100/Patterns

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Observable 24 https://github.com/CSC3100/Patterns

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Classroom | New Version 25 https://github.com/CSC3100/Patterns

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Student | New Version 26 https://github.com/CSC3100/Patterns

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Teacher | New Version 27 https://github.com/CSC3100/Patterns

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Important 28 Do not reinvent the wheel! (Do not make another implementation for classes Observer or Observable -they already exist in libraries!)

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Important 29 Depreciated java.util.Observer java.util.Observable The implementation of these packages That is NOT about the Observer pattern being depreciated.

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Important 30 Use java.beans.PropertyChangeListener java.beans.PropertyChangeSupport

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Classroom | Listener Version 31 https://github.com/CSC3100/Patterns

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Student | Listener Version 32 https://github.com/CSC3100/Patterns

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Teacher | Listener Version 33 https://github.com/CSC3100/Patterns

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Thoughts? 34

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Homework 35 Reading https://medium.com/swlh/software-design-patterns-why-what-and-an-example-8d4c0934a6ca

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Test Yourselves

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Problem • Im a gine a cl a ss Te a cher running in its own execution thre a d, forever gr a ding—recording gr a des a s a collection of numeric a l v a lues. • A p a nel (PrinterP a nel) would like to show the gr a des a s they a re gener a ted. • Another p a nel (St a tistic a lP a nel) would like to show re a l-time st a tistics a bout the gr a des (how m a ny p a ss a nd how m a ny f a il). 37

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Questions 38

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Lab.

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Lab 40 Draft a Class Diagram

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Code public class B implements E { public B() { C c1 = new C(); } public void method(X x) { x.m() B b = new B(); b.sleep(); } } public class Y { X x = new X(); B b = new B(); } public class A extends B { C c1, c2; public A() { c1 = new C(); } public void method() { D d = new D(); d.working(); } } public class X { B var = new A(); public void m() { double x – Math.sqrt(5); } }

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Let’s work 42

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CSC 307 Introduction to Software Engineering Javier Gonzalez-Sanchez, Ph.D. [email protected] Spring 2025 Copyright. These slides can only be used as study material for the class CSC307 at Cal Poly. They cannot be distributed or used for another purpose.