How to build SOLID code
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The document discusses principles for writing solid code, emphasizing clarity and maintainability. It outlines common pitfalls like singletons, tight coupling, and untestability, along with principles such as single responsibility, open/closed, and dependency inversion. The presentation encourages developers to avoid bad practices and adopt solid design principles for better code quality.
![Liskov Substitution Principle
#zenetr
public class Rectangle {
protected int width;
protected int height;
public int getArea() { return width * height; }
public void setWidth(int width) { this.width = width; }
public void setHeight(int height) { this.height = height; }
}
public class Square extends Rectangle {
public void setWidth(int width) { this.width = width; this.height = width; }
public void setHeight(int height) { this.width = height; this.height = height; }
}
public class Main {
public static void main(String[] args) {
Rectangle rectangle = new Square();
rectangle.setWidth(10); rectangle.setHeight(20);
assert rectangle.getArea() == 200; // this will fail!
}
}](https://image.slidesharecdn.com/howtobuildsolidcode-140525071639-phpapp02/85/How-to-build-SOLID-code-29-320.jpg)
How to build SOLID code
- 1. How to build SOLID code Sebastiano (eTr) Merlino
- 3. Almost entirely copied from inspired by the presentation “From STUPID to SOLID” by William Durand. #zenetr
- 4. DISCLAIMER: I give you an opinion not rules. Please, consider these just as principles, not laws! #zenetr
- 5. Only 2 types of code do exist: Your code: Other people code: It’s REASSURING and you understand it It INTIMIDATES you and it’s ~99. 999% of world’s code #zenetr
- 6. Why should my code be clear? Because we READ much more than we WRITE #zenetr
- 8. What makes code STUPID? ● Singleton ● Tight Coupling ● Untestability ● Premature Optimization ● Indescriptive Naming (yeah! It’s not misspelled) ● Duplication #zenetr
- 10. Singleton ● It represents a GLOBAL STATE in your code ● Programs using global state are VERY difficult to test and debug ● Programs relying on global state HIDE their dependencies Links: - Why singletons are controversial? - Why is singleton an antipattern? - So Singletons are bad, then what? #zenetr
- 12. Tight Coupling ● Generalization of the singleton ISSUE ● If changing something in a module FORCES you to change also another module ● It makes code difficult to REUSE and also difficult to TEST ● To avoid it, favor COMPOSITION over inheritance and try to use DEPENDENCY INJECTION where possible. Links: - Reducing Coupling (Martin Fowler) #zenetr
- 14. Untestability ● Testing should not be HARD ● Whenever you don’t write UNIT TESTS because you DON’T HAVE TIME, the real issue is that your code is BAD ● Most of the time untestability is caused by TIGHT COUPLING #zenetr
- 16. Premature Optimization PREMATURE OPTIMIZATION is the root of all evil - DONALD KNUTH ● Do not OVER-COMPLICATE your system in order to optimize it ● There is only COST and no BENEFIT ● MEASURE the performances before you start to optimize DON’T DO IT. For experts only: DON’T DO IT NOW! Links: - Premature Optimization Anti-Pattern #zenetr
- 18. Indescriptive Naming ● Name your classes, methods, attributes and variables properly ● Don’t abbreviate, NEVER! ● If you are not able to give your class a short name, maybe its responsibilities are not WELL DEFINED ● Programming languages are for HUMANS #zenetr
- 20. Duplication ● If you do it, you will find yourself changing your code in multiple places. ● Don’t Repeat Yourself (DRY) ● Keep It Simple, Stupid! (KISS) ● Be DRY not WET (We Enjoy Typing) Links: - No, seriously. Don’t repeat yourself - DRY principle - KISS principle #zenetr
- 21. #zenetr
- 22. SOLID Term describing a collection of design principles for GOOD CODE that was coined by ROBERT C. MARTIN aka UNCLE BOB #zenetr
- 23. What makes code SOLID? ● Single Responsibility Principle ● Open/Closed Principle ● Liskov Substitution Principle ● Interface Segregation Principle ● Dependency Inversion Principle #zenetr
- 25. Single Responsibility Principle ● There should NEVER be more than ONE reason for a class to change ● Split big classes ● Use LAYERS ● Avoid GOD classes ● Write STRAIGHTFORWARD comments Links: - Single Responsibility Principle #zenetr
- 27. Open/Closed Principle ● Software entities should be OPEN for extension but CLOSED for manipulation ● Make ALL member variables private ● NO global variables, EVER ● Avoid SETTERS (as much as possible) ● Builder Pattern + Immutable Objects Links: - Open/Closed Principle #zenetr
- 29. Liskov Substitution Principle #zenetr public class Rectangle { protected int width; protected int height; public int getArea() { return width * height; } public void setWidth(int width) { this.width = width; } public void setHeight(int height) { this.height = height; } } public class Square extends Rectangle { public void setWidth(int width) { this.width = width; this.height = width; } public void setHeight(int height) { this.width = height; this.height = height; } } public class Main { public static void main(String[] args) { Rectangle rectangle = new Square(); rectangle.setWidth(10); rectangle.setHeight(20); assert rectangle.getArea() == 200; // this will fail! } }
- 30. Liskov Substitution Principle #zenetr ● Objects in a program should be replaceable with instances of their subtypes WITHOUT ALTERING THE CORRECTNESS of the program Links: ● Liskov Substitution Principle ● Circle-ellipse problem ● Should sets inherit from bags?
- 32. Interface Segregation Principle #zenetr ● MANY client-specific interfaces are BETTER THAN ONE general- purpose interface. ● You should not have to implement methods you don’t use ● Enforcing ISP gives you LOW COUPLING and HIGH COHESION ● KEEP COMPONENTS FOCUSED and MINIMIZE DEPENDENCIES BETWEEN THEM Links: ● Interface Segregation Principle ● Coupling and Cohesion: Principles of Orthogonal OOP
- 34. Dependency Inversion Principle #zenetr ● High level modules SHOULD NOT DEPEND upon low level modules. Both SHOULD DEPEND upon abstractions ● Abstractions should not depend upon details. Details should depend upon abstractions ● Use the same level of abstraction at a given level ● It REDUCES DEPENDENCY on implementation specifics and makes code MORE REUSABLE Links: ● Dependency Inversion Principle ● Programming to the interface
- 35. Rule of thumb: USE YOUR BRAIN! #zenetr
- 38. License: Creative Commons Attribution-ShareAlike 3.0 Unported License #zenetr