Clean code - Agile Software Craftsmanship

Use pronounceable names
class DtaRcrd102
class DtaRcrd102 class Customer
class Customer

class InchToPointConvertor {
//convert the quantity in inches to points.
//convert the quantity in inches to points.
static float parseInch(float inch) {
static float parseInch(float inch) {
return inch * 72; //one inch contains 72
return inch * 72; //one inch contains 72
points.
points.
}}
}}


final static int POINTS_PER_INCH=72;
final static int POINTS_PER_INCH=72;

static float convertToPoints(float inch) {
static float convertToPoints(float inch) {
return inch * POINTS_PER_INCH;
return inch * POINTS_PER_INCH;
}}
}}

class Account {
class Account {
//check if the password is complex enough, i.e.,
//check if the password is complex enough, i.e.,
//contains letter and digit/symbol.
//contains letter and digit/symbol.
boolean isComplexPassword(String password) {{
boolean isComplexPassword(String password)
//found aa digit or symbol?
//found digit or symbol?
boolean dg_sym_found=false;
boolean dg_sym_found=false;
//found aa letter?
//found letter?
boolean letter_found=false;
boolean letter_found=false;
for(int i=0; i<password.length(); i++){
for(int i=0; i<password.length(); i++){
char c=password.charAt(i);
char c=password.charAt(i);
if(Character.isLowerCase(c)||Character.isUpperCase(c))
if(Character.isLowerCase(c)||Character.isUpperCase(c))
letter_found=true;
letter_found=true;
else dg_sym_found=true;
else dg_sym_found=true;
}}
return (letter_found) && (dg_sym_found);
return (letter_found) && (dg_sym_found);
}}
}}
class Account {
class Account {
boolean isComplexPassword(String password){
boolean isComplexPassword(String password){
return containsLetter(password) &&
return containsLetter(password) &&
(containsDigit(password) ||
(containsDigit(password) ||
containsSymbol(password));
containsSymbol(password));
}}
boolean containsLetter(String password) {{
boolean containsLetter(String password)
return false;
return false;
}}
boolean containsDigit(String password) {{
boolean containsDigit(String password)
return false;
return false;
}}
boolean containsSymbol(String password) {{
boolean containsSymbol(String password)
return false;
return false;
}}

Goal of OOAD:
Identify the classes and relations between them for a given
problem.

Read the problem statement carefully and identify:
• Nouns (Classes)
• Verbs (Behavior)
• Actors (Users)

Identify relationships between classes
• Is-A (Generalization / Inheritance)
• Has-A (Composition)
• Uses (Dependency)

A basket contains oranges 11
Basket
Basket
and apples.

** **
Apple
Apple Orange
Orange

11 **
Fruits have cost Basket
Basket Fruit
Fruit
int Price;
int Price;

Apple
Apple Orange
Orange

Generalize to accommodate new requirements.
Generalize to accommodate new requirements.
Slide 34

A user has password. Password can be encrypted and decrypted.

11 11
User
User Password
Password
public String encrypt();
String userid;
String userid; public String decrypt();
public String decrypt();

Password is encrypted using a encryption service.

11 11
User
User Password
Password EncryptionService
EncryptionService
public String encrypt(); public String encrypt(String);
public String encrypt(String);
String userid;
String userid; public String decrypt();
public String decrypt(); public String decrypt(String);
public String decrypt(String);

Slide 35

Class should have one and only one reason to change.

Rectangle
Rectangle Rectangle
Rectangle
Point topLeftCorner
Point topLeftCorner
public draw()
public draw()
Point bottomRightCorner
Point bottomRightCorner
public area()
public area()

Two responsibilities:
1.Mathematical model of the geometry of rectangle
2.Render rectangle to a graphical user interface. Geometric
Geometric
Rectangle
Rectangle
public area()
public area()

Slide 36

Module should not know internal details of objects it manipulates.
A method M of an object O may only invoke the methods of the
following kinds of objects:
•O itself
•M's parameters
•any objects created/instantiated within M Class PaperBoy { {
Class PaperBoy
•O's instance variables void collectPaymetents() { {
void collectPaymetents()
Class PaperBoy { {
Class PaperBoy float payment ==2.0;
float payment 2.0;
void collectPaymetents() { {
void collectPaymetents() float fundsCollected ==0.0;
float fundsCollected 0.0;
float payment ==2.0;
float payment 2.0; for (Customer customer : :customerList) { {
for (Customer customer customerList)
float fundsCollected ==0.0;
float fundsCollected 0.0;
try { {
try
for (Customer customer : :customerList) { {
for (Customer customer customerList) fundsCollected +=
fundsCollected +=
customer.makePayment(payment);
float moneyInWallet ==customer.getWallet().getMoney(); customer.makePayment(payment);
float moneyInWallet customer.getWallet().getMoney(); }}
catch (NotEnoughMoneyComeLaterException
catch (NotEnoughMoneyComeLaterException
ifif(moneyInWallet >= payment) { {
(moneyInWallet >= payment) e) { {
e)
customer.getWallet.setMoney(moneyInWallet ––
customer.getWallet.setMoney(moneyInWallet }}
payment);
payment); }}
fundsCollected += payment;
fundsCollected += payment; }}
}}
}}
} } Slide 37
}}

In object oriented languages, power of polymorphism comes from Liskov’s
substitution principle.

“A subclass can be used as an argument where a base class is expected”

Class Mechanic { {
Class Mechanic

public void repair (Car car) { {
public void repair (Car car)

}}

}}

class HyundaiCar implements Car { {
class HyundaiCar implements Car
}}

class MarutiCar implements Car { {
class MarutiCar implements Car
}}
HyundaiCar faultyHyundai ==new HyundaiCar();
HyundaiCar faultyHyundai new HyundaiCar();
mechanic.repair (faultyHyunai);
mechanic.repair (faultyHyunai);
class HyundaiSantro extends HyundaiCar { {
class HyundaiSantro extends HyundaiCar MarutiCar faultyMaruti ==new MarutiCar();
MarutiCar faultyMaruti new MarutiCar();
}}
mechanic.repair(faultyMaruti);
mechanic.repair(faultyMaruti);
Slide 38

Class Driver { {
Class Driver

public void drive (Car car) { {
public void drive (Car car)

}}

public void drive (Truck truck) { {
public void drive (Truck truck)

}}
}}

Class Driver { {
Class Driver

public void drive (Vehicle vehicle) { {
public void drive (Vehicle vehicle)

}}

}}

Slide 39

Class should be open for extension, but closed for modification.

ifif( (isGoingToMovie() ) ){ {
isGoingToMovie()

Vehicle vehicle ==new Car();
Vehicle vehicle new Car();

driver.drive (vehicle ) )
driver.drive (vehicle

}}
Vehicle vehicle ==getVehicle(conditions);
Vehicle vehicle getVehicle(conditions);
else ( (ifRelocatingToNewHome ()()) ){ {
else ifRelocatingToNewHome driver.drive (vehicle ););
Vehicle vehicle ==new Truck();
Vehicle vehicle new Truck();

driver.drive (vehicle ););

}}

Slide 40

Extract Try/Catch Blocks
Error Handling Is One Thing

List<Employee> employees = getEmployees();
for(Employee e : employees) {
totalPay += e.getPay();
}
public List<Employee> getEmployees() {
if( .. there are no employees .. )
return Collections.emptyList();
}

public double xProjection(Point p1, Point p2) {
return (p2.x – p1.x) * 1.5;
}
public double xProjection(Point p1, Point p2) {
if (p1 == null || p2 == null) {
throw InvalidArgumentException ("Invalid argument
for MetricsCalculator.xProjection");
}
return (p2.x – p1.x) * 1.5;
}

Clean code - Agile Software Craftsmanship

Clean code - Agile Software Craftsmanship

More Related Content

What's hot

Viewers also liked

Similar to Clean code - Agile Software Craftsmanship

Clean code - Agile Software Craftsmanship