Clean Code

Clean Code
// by Ingo Schwarz

What‘s the content?
// try to find a simple definition
What is Clean Code?
// try to convince them, so you don‘t have to force them
Why do I need Clean Code?
// show some simple rules
How to produce Clean Code?

What is Clean Code?
Bjarne Stroustrup
“I like my code to be
elegant and efficient“
“Clean code does
one thing well“

What is Clean Code?
Grady Booch
“Clean code is
Simple and direct“
“Clean code reads like
well-written prose“

What is Clean Code?
Dave Thomas
“Clean code can be read“
“Clean code should
be literate“

What is Clean Code?
Michael Feathers
“Clean Code always looks
like it was written by someone
who cares“

What is Clean Code?
Ward Cunningham
“You know you are working
on clean code, when each routine
you read turns out to be
the pretty much what you
expected“

What is Clean Code?
How to measure good code?

…because you are an author
// YES, YOU ARE!!!
“An author is someone
who practices writing as a profession“
by somebody

…because you don‘t want to be a verb
// NO, YOU DON‘T!!!
“Oh man, this code has been Jimmy’d“
by somebody else

…because you are lazy
// YES, YOU ARE!!!
// so am I
// PROOF: no quotation at this slide

Robert C. Martin
(aka Uncle Bob)
“The Boy Scout Rule“
// General

// Naming
“Names are sound and smoke”
Johannes Wolfgang von Goethe – Faust I

Take care about names!
// we name everything:
// variables, functions, arguments, classes, packages
// Naming

public class DtaRcrd102 {
private Date genymdhms;
private Date modymdhms;
private static final String pszqint = “102“;
}
// Naming
Use Pronounceable Names

public class Customer {
private static final String RECORD_ID = “102“;
private Date generationTimestamp;
private Date modificationTimestamp;
}
// Naming
Use Pronounceable Names

private String m_dsc;
// Naming
Avoid Encodings (member prefixes)
private PhoneNumber phoneString;
Avoid Encodings (hungarian notation)

private String description;
// Naming
Avoid Encodings (member prefixes)
private PhoneNumber phone;
Avoid Encodings (hungarian notation)

Add Meaningful Context
fistName, lastName, street, city, state, zipcode
// a better solution
addressFirstName, addressLastName, addressState
// a better solution
Adress myAddress = new Address();
myAddress.getFirstName();
// Naming

Small!
Rules of Functions:
1. should be small
2. should be smaller than that
// < 150 characters per line
// < 20 lines
// Functions

Do One Thing
Functions should do ONE thing.
They should do it WELL.
They should do it ONLY.
// Functions

One Level of Abstraction
// high level of abstraction
getHtml();
// intermediate level of abstraction
String pagePathName = PathParser.getName( pagePath );
// remarkable low level
htmlBuilder.append(“n”);
// Functions

Switch Statements
class Employee {
int getSalary() {
switch( getType() ) {
case EmployeeType.ENGINEER:
return _monthlySalary;
case EmployeeType.SALESMAN:
return _monthlySalary + _commission;
case EmployeeType.MANAGER:
return _monthlySalary + _bonus;
default:
throw new InvalidEmployeeException();
}
}
}
// Functions

Switch Statements
interface Employee {
int getSalary();
}
class Salesman implements Employee {
int getSalary() {
return getMonthlySalary() + getCommision();
}
}
class Manager implements Employee {
…
}
// Functions

// niladic
getHtml();
// monadic
execute( boolean executionType );
// dyadic
assertEquals(String expected, String actual);
// triadic
drawCircle(double x, double y, double radius);
// Function Arguments

Improve Monadic Functions with Flag Argument
// ???
execute( boolean executionType );
// !!!
executeInSuite();
executeStandAlone();

Improve Dyadic Functions with two similar Argument Types
// ???
assertEquals(String expected, String actual);
assertEquals(String actual, String expected);
// !!!
assertExpectedEqualsActual(expected, actual);

Improve Triadic Functions with three similar Argument Types
// ???
drawCircle(double x, double y, double radius);
drawCircle(double radius, double x, double y);
// …
// !!!
drawCircle(Point center, double radius);

Don‘t comment bad code, rewrite it!
// Comments

Noise
/** Default Consturctor */
public AnnaulDateRule() { … }
/** The day of the Month. */
private int dayOfMonth();
/** Returns the day of the Month.
@return the day of the Month. */
public int getDayOfMonth() {
return dayOfMonth;
}
// Comments

Scary Noise
/** The name. */
private String name;
/** The version. */
private String version;
/** The licenseName. */
private String licenseName;
/** The version. */
private String info;
// Comments

Don‘t use comments if you can use a Function/Variable
// does the moduel from the global list <mod> depend on the
// subsystem we are part of?
if(smodule.getDependSubsystems()
.contains(subSysMod.getSubSystem())) { … }
// improved
ArrayList moduleDependencies = module.getDependentSubsystems();
String ourSubsystem = subSystemModule.getSubSystem();
if( moduleDependencies.contains( ourSubsystem ) ) { … }
// Comments

The Law of Demeter
// Bad
String outputDir = ctxt.getOptions()
.getScratchDir()
.getAbsolutePath();
// Good
String outputDir = ctxt.getScratchDirPath();
// Data Access

Prefer Exceptions to Returning Error Codes
if( deletePage( page ) == E_OK ) {
if( registry.deleteReference(page.name) == E_OK ) {
if( configKeys.deleteKey( page.name.makeKey() ) == E_OK ) {
logger.log(“page deleted”);
} else {
logger.log(“configKey not deleted”);
}
} else {
logger.log(“deleteReference from registry failed”);
}
} else {
logger.log(“delete failed”);
}
// Error Handling

Prefer Exceptions to Returning Error Codes
try {
deletePage(page);
registry.deleteReference(page.name);
configKeys.deleteKey(page.name.makeKey());
} catch( Exception e ) {
logger.log(e.getMessage());
}
// Error Handling

Extract Try/Catch Blocks
public void delete(Page page) {
try {
deletePageAndAllReferences( page );
} catch ( Exception e ) {
logError( e );
}
}
private void deletePageAndAllReferences(Page page) throws Exception {
deletePage( page );
registry.deleteReference(page.name);
configKeys.deleteKey(page.name.makeKey());
}
// Error Handling

Don‘t return Null
List<Employee> employees = getEmployees();
If( employees != null ) {
for( Employee employee : employees ) {
totalSalary += employee.getSalary();
}
}
// Error Handling

Don‘t return Null
List<Employee> employees = getEmployees();
for( Employee employee : employees ) {
totalSalary += employee.getSalary();
}
// Error Handling

Small!
Rules of Classes:
1. should be small
2. should be smaller than that
// Single Responsibility Principle (SRP)
// a class should have one, and only one, readon to change
// Classes

// More Information
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