Does Good Code Matter?

Gian Lorenzetto

Implementation Patterns

By Kent Beck

• 157 Pages / 77 Implementation Patterns

• Not a “patterns” book

• Java programming habits for creating readable code

• Conscious approach

• what do I want to tell the reader about this code?

• what does the code communicate what I am thinking to others?

This book is not ...

• Not a style guide

• Not a design book

• Not a patterns book (!?)

• Not a language guide

• Not for beginners (despite what Amazon thinks ...)

This book is ...• About writing good code for others -

• to read, to understand, to learn from and to extend

• For those who think life is too short to waste on bad code

• For those who delight in writing beautiful code

• Like spending a few hours inside Kent Beck’s head while he’s hacking JUnit

Premise

• “I have seen too much ugly code make too much money to believe that quality of code is either necessary or sufficient for commercial success or wide-spread use.”

• Communication - “ ... programming so other people can understand your code.”

• Does good code matter?

Book OverviewIntroduction

Class

Behavior

Methods

State

CollectionsFrameworks

• Patterns• Values & Principles• Motivation

Similar Logic Different Data

Dividing Logic Multi-Valued Data

1. Introduction

• Overview

• Question minute-to-minute decisions

• Why am I so sure this method should be called foo?

• Program consciously, for others

• Format - essays, diagrams, teaching story, examples

Design Pattern Language Guide

Implementation Patterns

Few per day

Every fewseconds

Regulate object interaction

Why choose a particular construct?

2. Patterns

• Programming laws (forces)

1. Read more often than written

2. No such thing as done

3. Structured using basic set of state and control flow concepts

4. Readers need to understand in detail and in concept

• Patterns illustrate a point of view about the relative priorities of these forces

3. A Theory of Programming

• Values

• Over-arching universal themes of programming

• Communication, Simplicity, Flexibility

• Principles

• Bridge the values

3. A Theory of Programming

Values PatternsPrinciples

MotivationTranslate motive

into actionWhat to do

• Principles

• Local consequences

• Minimize repetition

• Logic and data together

• Symmetry

• Declarative expression

• Rate-of-change

3. A Theory of Programming

4. Motivation

• cost total = cost develop + cost maintain

• Increase up front costs does not help

• Implementation patterns satisfy human and economic needs

5. Class

• Bundles related state

• Class

• Simple Superclass Name

• Interface

• Value Object

• Inner Class

• Conditional

6. State

• Communicate use of state

• Objects package:

• Behaviour (presented to outside world)

• State (supports behaviour)

• Objects make analysing state easier

6. State

• Patterns

• Access (Direct, Indirect)

• State (Common, Variable, Extrinsic)

• Variable (Local, Field, Parameter)

• Role Suggesting Name

• Declared Type

• Initialisation (Eager, Lazy)

The best intentions ...x = 10;

setX(10);

openGarageDoor(10);

openGarageDoor() { setX(10);}

7. Behaviour

• How to express behaviour of a program

• Control Flow

• Message (Choosing, Double Dispatch, Reversing, Inviting, Explaining)

• Guard Clause

• Exception

Guards, Guards!void initialise() { if (!isInitialised()) { ... }}

• One entry point, one exit point

void initialise() { if (isInitialised()) { return; } ...}

• Express simple and local exceptional situations with purely local consequences

• Highlight the difference between normal and exceptional processing

8. Methods

• Why divide logic into chunks?

• Readability, critical flow, understanding, communication ...

• Logic into methods

• Methods into classes

• Classes into packages

Communicateconnection of

logic

8. Methods• Deciding what goes where is hard

• Compose Method

• Intention-Revealing Name

• Method Visibility

• Method Object

• Collection Accessor

• Query Method

• Setting Method

9. Collections

• Patterns

• Metaphors

• Issues

• Interfaces (Array, Iterable, Collection ...)

• Implementations (Collection, List, Set, Map)

• Collections (Searching, Sorting, Unmodiiable, Single Element, Empty)

• Extending Collections

Example ...stripHeader();stripFooter();process();

Attempt 1

strip???();process();Attempt 2

findTableElement();process();

Attempt 3

The End