Java conventionsA.K.M. Ashrafuzzaman

Java code conventions

Some of the code conventions of Java, suggested by sun, followed by the article below, Code Conventions for the Java TM Programming Language Revised April 20, 1999

Java code conventions

● Indentation● Statements● Naming Conventions● Programming Practices Classes and methods good, bad and ugly

Indentation

Four spaces should be used as the unit of indentation  

Line Length

Avoid lines longer than 80 characters.

Wrapping Lines

Break after a comma someMethod(longExpression1, longExpression2, longExpression3, longExpression4, longExpression5); var = someMethod1(longExpression1, someMethod2(longExpression2, longExpression3));

Break before an operator longName1 = longName2 * (longName3 + longName4 - longName5) + 4 * longname6; // PREFER

longName1 = longName2 * (longName3 + longName4 - longName5) + 4 * longname6; // AVOID 

Wrapping Lines

Wrapping Lines

● If the above rules lead to confusing code or to code that's squished up against the right margin, just indent 8 spaces instead

● Align the new line with the beginning of the expression at the same level on the previous line

Wrapping Lines//CONVENTIONAL INDENTATIONsomeMethod(int anArg, Object anotherArg, String yetAnotherArg, Object andStillAnother) { ...} //INDENT 8 SPACES TO AVOID VERY DEEP INDENTSprivate static synchronized horkingLongMethodName(int anArg, Object anotherArg, String yetAnotherArg, Object andStillAnother) { ...}

Wrapping Lines

//DON'T USE THIS INDENTATIONif ((condition1 && condition2) || (condition3 && condition4) ||!(condition5 && condition6)) { //BAD WRAPS doSomethingAboutIt(); //MAKE THIS LINE EASY TO MISS}

//USE THIS INDENTATION INSTEADif ((condition1 && condition2) || (condition3 && condition4) ||!(condition5 && condition6)) { doSomethingAboutIt();}

//OR USE THISif ((condition1 && condition2) || (condition3 && condition4) ||!(condition5 && condition6)) { doSomethingAboutIt();}

Statements

if (condition) { statements;} else if (condition) { statements;} else { statements;}

Always prefer foreach statement//ugly codevoid cancelAll(Collection<TimerTask> c) { for (Iterator<TimerTask> i = c.iterator(); i.hasNext(); ) i.next().cancel();}//clean codevoid cancelAll(Collection<TimerTask> c) { for (TimerTask t : c) t.cancel();}

Statements

Naming Conventions

Packages● all lower case● starts with domain name[ com, edu, gov,

mil, net, org]● the rest is organizational standardsExamplescom.sun.engcom.apple.quicktime.v2edu.cmu.cs.bovik.cheese

Naming Conventions

Classes/Interfaces● Should be noun● Cap init camel case Note: If you can not name a class then that is an indication of "Something went wrong, when you were splitting the responsibility"

Naming Conventions

Methods● Should be verbs● Init small camel case Examplesrun(); getBackground();findByUser(user);

Naming Conventions

Variables● Init small camel case● meaningful ExampleProduct product;List<Product> products; Note: Usually IDE suggestions are good candidates.

Naming Conventions

Constants● All caps separated by '_' Examplesstatic final int MIN_WIDTH = 4;static final int MAX_WIDTH = 999;static final int GET_THE_CPU = 1;

Programming Practices

Providing Access to Instance and Class Variables● Don't make any instance or class variable

public

Programming Practices

Referring to Class Variables and Methods Use class to access the method, as the responsibility goes to the class not the object. AClass.classMethod(); //OKanObject.classMethod(); //AVOID!

Programming Practices

Keep the code consiseif (booleanExpression) { return true;} else { return false;}should instead be written as,return booleanExpression;

Programming Practices

if (condition) { return x;}return y; Better be, return (condition ? x : y);

Classes, objects and methods

Thinking in terms of "object"Not as easy as you think

Object

Object Property

Behaviour

Has

Has

Object

● An actor (Noun)● Has some properties● Has some behavior

Object

Example● An actor (Noun) => Car● Has some properties => Fuel● Has some behavior => start, stop,

accelerate, etc

Object

Nothing specialright???

Object

car.addFuel(10);

Object

car.start();

Object

Now let us say we have a driver

Object

● Driver drives a car● A car is driven by a driver

Car DriverDriven by Drives

The big question

???.addFuel(10); 

VS

Object

● Responsibility● Which object is being impacted

○ Which are the properties that are changed○ Which object has changed his behavior

car.addFuel(10);

Object

Anyone can add fuel to the car, even the driver Class Driver { ...

public void refillCar() { car.addFuel(10); }}

Methods

Behavior of an object,that can change the properties of

that object

Relationships

How we set the relationship of driver with the car ???

Relationships

Relationships

● Driver owns a car● Driver drives a car● Loves a car

In short

When we design a software● Search for classes (Entity)● Search for behavior● Identify which is the behavior of which

entity● Identify the relationship between the

entities

Methods

● Should properly express an action● Should have very few arguments● Should be readable as a plain english

language not as a geeky programming language

● Better be an active voice● Should be short, should look like a pseudo

code, which means the details should be hidden in the sub methods

Methods

Examplesuser.isPermitedToEdit(task);story.totalEstimatedHours();classService.findClassesFor(user);classService.findClasseByTeacherAndSemester(teacher, semester);

Conclusion

● Follow the conventions● Any code is 20% of its time is written and

80% time is read, so write it well● Top level method should only contain a

pseudo code● Methods should be small● Think in terms of object and identify

responsibilty