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Exploring general development principles

From: Foundations of Programming: Object-Oriented Design

Video: Exploring general development principles

First, we're going to go through some general development principles, some obvious and some not so obvious. Now, one well-known idea in software development--and not just limited to Object-Oriented Design but still worth mentioning--is D-R-Y or DRY: Don't Repeat Yourself. Now, the very obvious impact of this is we don't copy and paste unchanged blocks of code from one place to another, we contain them in functions or methods. But what's not so obvious is the idea that this can be applied in multiple areas.

Exploring general development principles

First, we're going to go through some general development principles, some obvious and some not so obvious. Now, one well-known idea in software development--and not just limited to Object-Oriented Design but still worth mentioning--is D-R-Y or DRY: Don't Repeat Yourself. Now, the very obvious impact of this is we don't copy and paste unchanged blocks of code from one place to another, we contain them in functions or methods. But what's not so obvious is the idea that this can be applied in multiple areas.

We don't just want to avoid duplication in code, but in our database schemas, in our diagrams, in our documentation, and more than that, there should be a single source of truth. There should be one place in our system that deals with the particular problem. One place that that gets taken care of, whether that's handling a business problem or storing or calculating a piece of data. And then there's YAGNI, Y-A-G-N-I: You Ain't Gonna Need It. Solve the problems that you know exist, don't write speculative code, solve today's problems.

Now, this is why we want to at the very least have basic user stories or use cases so that when we're buried in our code editor we're not actually trying to figure out what we're actually attempting to solve. It's very tempting for developers when writing code, when solving a problem, to add in some extra functionality for something that seems like it might be necessary in the future. But that's not a great thing to do. Everything you add is code that needs to be maintained, it needs to be tested, it needs to be debugged, and it's easy for this to lead to feature-creep, or just general code bloat.

So unnecessary code and duplicated code are what are sometimes referred to as a Code Smell. Code Smells are a great term for when reading code, either your own, or someone else's. The code may be valid, it may work, it may compile, but there is something about it that just doesn't smell right. It's often a clue, a warning sign of a deeper problem, and here are just a few examples of what I mean by a Code Smell. One would be the idea of a long method. You open up a method to read it, it has got 250, 300 lines.

This is the kind of thing that really needs to be split up into much smaller methods. Or working with very short or very long identifiers. Aside from using letters like I for indexes and iteration, you shouldn't be expecting to see variables called A and B and C in real code. Another clue would be pointless comments. Yes, code should be commented and code should be well-written so that it's readable and the code comments itself. We do want comments, but we don't want comments like this, where the comment is actually longer than the code that it's describing.

More specifically when doing Object- Oriented Design, we have Code Smells like the God object. This is where you have one master object that tries to do everything in the program, or at least one object that seems to be doing very different responsibilities that have nothing to do with each other. This is very common when procedural programmers start working in an object-oriented language, but the only change they learned was the syntax of the language and not the principles behind them. It's a clue that this needs to be revisited and broken apart into the right kind of objects.

And then there's Feature envy. If a class seems to do very little except use all the methods of one other class, it's another sign that you need to rethink the roles of one or the other. So those are just a few examples, and in the next section I'm going to cover some more formalized and object- oriented specific principles that we can use.

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Foundations of Programming: Object-Oriented Design

47 video lessons · 48277 viewers

Simon Allardice
Author

 
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  1. 11m 35s
    1. Welcome
      1m 25s
    2. Who this course is for
      1m 15s
    3. What to expect from this course
      3m 6s
    4. Exploring object-oriented analysis, design, and development
      1m 41s
    5. Reviewing software development methodologies
      4m 8s
  2. 26m 14s
    1. Why we use object-orientation
      2m 42s
    2. What is an object?
      5m 22s
    3. What is a class?
      4m 43s
    4. What is abstraction?
      2m 45s
    5. What is encapsulation?
      3m 45s
    6. What is inheritance?
      3m 35s
    7. What is polymorphism?
      3m 22s
  3. 12m 16s
    1. Understanding the object-oriented analysis and design processes
      4m 13s
    2. Defining requirements
      6m 9s
    3. Introduction to the Unified Modeling Language (UML)
      1m 54s
  4. 23m 35s
    1. Understanding use cases
      6m 11s
    2. Identifying the actors
      4m 16s
    3. Identifying the scenarios
      5m 7s
    4. Diagramming use cases
      4m 18s
    5. Employing user stories
      3m 43s
  5. 16m 36s
    1. Creating a conceptual model
      1m 59s
    2. Identifying the classes
      2m 27s
    3. Identifying class relationships
      2m 38s
    4. Identifying class responsibilities
      6m 43s
    5. Using CRC cards
      2m 49s
  6. 22m 25s
    1. Creating class diagrams
      6m 11s
    2. Converting class diagrams to code
      4m 57s
    3. Exploring object lifetime
      5m 55s
    4. Using static or shared members
      5m 22s
  7. 19m 49s
    1. Identifying inheritance situations
      6m 49s
    2. Using inheritance
      2m 43s
    3. Using abstract classes
      2m 2s
    4. Using interfaces
      4m 20s
    5. Using aggregation and composition
      3m 55s
  8. 9m 23s
    1. Creating sequence diagrams
      5m 18s
    2. Working with advanced UML diagrams
      2m 3s
    3. Using UML tools
      2m 2s
  9. 10m 39s
    1. Introduction to design patterns
      2m 40s
    2. Example: the singleton pattern
      4m 53s
    3. Example: the memento pattern
      3m 6s
  10. 21m 47s
    1. Introduction to object-oriented design principles
      2m 50s
    2. Exploring general development principles
      3m 55s
    3. Introduction to SOLID principles
      6m 43s
    4. Introduction to GRASP principles
      8m 19s
  11. 7m 1s
    1. Reviewing feature support across different object-oriented languages
      3m 50s
    2. Additional resources
      2m 27s
    3. Goodbye
      44s

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