Java conventions

Java conventions
A.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));

Wrapping Lines
Break before an operator

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

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

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 INDENTATION
someMethod(int anArg, Object anotherArg, String yetAnotherArg,
Object andStillAnother) {
...
}

//INDENT 8 SPACES TO AVOID VERY DEEP INDENTS
private static synchronized horkingLongMethodName(int anArg,
Object anotherArg, String yetAnotherArg,
Object andStillAnother) {
...
}

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

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

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

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

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

Naming Conventions
Packages
● all lower case
● starts with domain name[ com, edu, gov,
mil, net, org]
● the rest is organizational standards
Examples
com.sun.eng
com.apple.quicktime.v2
edu.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

Examples
run();
getBackground();
findByUser(user);

Naming Conventions
Variables
● Init small camel case
● meaningful

Example
Product product;
List<Product> products;

Note: Usually IDE suggestions are good candidates.

Naming Conventions
Constants
● All caps separated by '_'

Examples
static 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

Referring to Class Variables and Methods

Use class to access the method, as the
responsibility goes to the class not the object.

AClass.classMethod(); //OK
anObject.classMethod(); //AVOID!

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

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

Has
Object Property

Has
Behaviour

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 special
right???

Object
Now let us say we have a driver

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

Driven by Drives
Car Driver

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
● 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
Examples
user.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

Java conventions

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