Clean code Bites

Applying clean code

Roy Nitert

28-3-2012

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Agenda

Why clean code What is clean code Examples:o SRPo Small methodso Descriptive nameso Parameterso DRY

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Why clean code ?

So it is easier to understand (readability) and cheaper to modify (maintainability) software

The code you write will be read more times than it was written and by more people.

Focus on the small things that make us better programmers.

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What is clean code ?

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What is clean code ?

http://en.wiktionary.org/wiki/clean_code

Noun

clean code (plural clean codes)

(idiomatic) software code that is formatted correctly and in an organized manner so that another coder can easily read or modify it.

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What is clean code ?

Characteristics of clean code: Small methods and classes Descriptive names Not too many parameters in methods (and no flags) No obvious or irrelevant comments (code must be

self describing) No redundancy (DRY: don’t repeat yourself) No magic numbers Single responsibility principle (SRP) Uniform coding style

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SRP: Single Responsibility Principle

every object should have a single responsibility, and that responsibility should be entirelyencapsulated by the class.

a class or module should haveone, and only one, reason to change

If class names have ‘manager’ or ‘processor’ in them, they probably have multiple responsibilities

the "S" in "SOLID" stands for the single responsibility principle (“Principles Of OOD”, Robert C. Martin)

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SRP example

Public class DashboardManager {

public Component getLastFocusedComponent();

public void setLastFocused(Component lastFocused);

public int getMajorVersionNumber();

public int getMinorVersionNumber();

public int getBuildNumber();

}

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SRP example

Public class FocusedComponent {

public Component getLastFocusedComponent();

public void setLastFocused(Component lastFocused);

Public class Version {

public int getMajorVersionNumber();

public int getMinorVersionNumber();

public int getBuildNumber();

}

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Small methods

They should be very very small Should do one thing, do it well, do it only One level of abstraction Should read like a narrative Should not have sections Blocks within if, else and while

statements should be one line long

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Small methods example

public static String renderPageWithSetupsAndTeardowns(

PageData pageData, boolean isSuite

) throws Exception {

boolean isTestPage = pageData.hasAttribute(“Test”);

if (isTestPage) {

WikiPage testPage = pageData.getWikiPage();

StringBuffer newPageContent = new StringBuffer();

includeSetupPages(testPage, newPageContent, isSuite);

newPageContent.append(pageData.getContent());

includeTeardownPages(testPage, newPageContent, isSuite);

pageData.setContent(newPageContent.toString());

}

return pageData.getHTML();

}

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Small methods example

public static String renderPageWithSetupsAndTeardowns(

PageData pageData, boolean isSuite

) throws Exception {

if (isTestPage(pageData))

includeSetupAndTeardownPages(pageData, isSuite);

return pageData.getHTML();

}

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Descriptive names

Names make software readable Helps clarify the design in your mind Use long names for long scopes Avoid encodings

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Descriptive names example

Public int x() {

int q = 0;

int z = 0;

for (int kk = 0; kk < 10; kk++) {

if (l[z] == 10) {

q += 10 + (l[z + 1] + l[z + 2]);

z += 1;

} else if (l[z] + l[z + 1] == 10) {

q += 10 + l[z + 2];

z += 2;

} else {

q += l[z] + l[z + 1];

z += 2;

}

}

return q;

}

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Descriptive names example

Public int score() {

int score = 0;

int frame = 0;

for (int frameNumber = 0; frameNumber < 10; frameNumber++) {

if (isStrike(frame)) {

score += 10 + nextTwoBallsForStrike(frame);

frame += 1;

} else if (isSpare(frame)) {

score += 10 + nextBallForSpare(frame);

frame += 2;

} else {

score += TwoBallsInFrame(frame);

frame += 2;

}

}

return score;

}

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Parameters / arguments

Small number: Zero is best, followed by one, two or three

More than three is questionable Output arguments are counterintuitive Boolean arguments (flags) loudly declare than

the function does more than one thing Simpler is easy to understand and easy to test Reduce number of arguments by creating

objects out of them

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Parameters example

Circle makeCircle(double x, double y, double radius);

public void AlignTaskCanBeStopped(bool useRealXps);

AlignTaskCanBeStopped(true);

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Parameters example

Circle makeCircle(Point center, double radius);

public void AlignTaskCanBeStoppedWith RealXps();

public void AlignTaskCanBeStoppedWith SimulatedXps();

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Don’t repeat yourself

Duplication DRY principle (Dave Thomas) Once, and only once (Kent Beck) Duplication is a missed opportunity for abstraction Examples:o Identical code (copy/paste)o Switch/case (or if/else) chainso Similar algorithms

Design patterns and OO itself are strategies for eliminating duplication

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DRY example

public void scaleToOneDimension( float desiredDimension, float imageDimension) {

if (Math.abs(desiredDimension – imageDimension) < errorThreshold)

return;

float scalingFactor = desiredDimension / imageDimension;

scalingFactor = (float)(Math.floor(scalingFactor * 100) * 0.01f);

RenderOp newImage = ImageUtilities.getScaledImage( image, scalingFactor, scalingFactor);

image.dispose();

System.gc();

image = newImage;

}

public synchronized void rotate(int degrees) {

RenderOp newImage = ImageUtilities.getRotatedImage( image, degrees);

image.dispose();

System.gc();

image = newImage;

}

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DRY example

public void scaleToOneDimension( float desiredDimension, float imageDimension) {

if (Math.abs(desiredDimension – imageDimension) < errorThreshold)

return;

float scalingFactor = desiredDimension / imageDimension;

scalingFactor = (float)(Math.floor(scalingFactor * 100) * 0.01f);

replaceImage(ImageUtilities.getScaledImage( image, scalingFactor, scalingFactor));

}

public synchronized void rotate(int degrees) {

replaceImage(ImageUtilities.getRotatedImage( image, degrees));

}

private void replaceImage(RenderedOp newImage) {

image.dispose();

System.gc();

image = newImage;

}

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Applying clean code

Know how to write clean code Think about these small improvements

during:o New developmento Code reviewso Changing codeo Fixing bugs

So code will be easier to understand and cheaper to modify

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Conclusion

Write code as if the person who is going to maintain it, is a psychopath who knows

where you live.

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Questions?

25© Sioux 2012 | Confidential |

roy.nitert@sioux.eu

+31 (0)40 2677100