Abbreviations and acronyms should not be uppercase when used as a part of a name.

exportHtmlSource();
openDvdPlayer();

    

    


    
    

exportHTMLSource();
openDVDPlayer();

    

    


    
    

Variables with a large scope should have long names, variables with a small scope can have short names.

Scratch variables used for temporary storage or indices can be kept short. A programmer reading such variables should be able to assume that its value is not used outside a few lines of code. Common scratch variables for integers are i, j, k, m, n and for characters c and d.

Rationale: When the scope is small, the reader does not have to remember it for long.

Plural form should be used on names representing a collection of objects.

Collection<Point> points;
int[] values;

    

    


    
    

Rationale: Enhances readability since the name gives the user an immediate clue of the type of the variable and the operations that can be performed on its elements. One space character after the variable type is enough to obtain clarity.

Associated constants should have a common prefix.

static final int COLOR_RED   = 1;
static final int COLOR_GREEN = 2;
static final int COLOR_BLUE  = 3;

    

    


    
    

Rationale: This indicates that they belong together, and make them appear together when sorted alphabetically.

Place line break to improve readability

When wrapping lines, the main objective is to improve readability. Do not always accept the auto-formatting suggested by the IDE.

In general:

• Break after a comma.

• Break before an operator. This also applies to the following "operator-like" symbols: the dot separator ., the ampersand in type bounds <T extends Foo & Bar>, and the pipe in catch blocks catch (FooException | BarException e)

totalSum = a + b + c
        + d + e;
setText("Long line split"
        + "into two parts.");
method(param1,
        object.method()
                .method2(),
        param3);

    

    


    
    

• A method or constructor name stays attached to the open parenthesis ( that follows it.

someMethodWithVeryVeryVeryVeryVeryVeryVeryVeryVeryVeryVeryLongName(
        int anArg, Object anotherArg);

    

    


    
    

someMethodWithVeryVeryVeryVeryVeryVeryVeryVeryVeryVeryVeryLongName
        (int anArg, Object anotherArg);

    

    


    
    

• Prefer higher-level breaks to lower-level breaks. In the example below, the first is preferred, since the break occurs outside the parenthesized expression, which is at a higher level.

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

    

    


    
    

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

    

    


    
    

• Here are two acceptable ways to format ternary expressions:

alpha = (aLongBooleanExpression) ? beta : gamma;
alpha = (aLongBooleanExpression)
        ? beta
        : gamma;

    

    


    
    

White space within a statement

It is difficult to give a complete list of the suggested use of whitespace in Java code. The examples below however should give a general idea of the intentions.

Rationale: Makes the individual components of the statements stand out and enhances readability.

Logical units within a block should be separated by one blank line.

// Create a new identity matrix
Matrix4x4 matrix = new Matrix4x4();

// Precompute angles for efficiency
double cosAngle = Math.cos(angle);
double sinAngle = Math.sin(angle);

// Specify matrix as a rotation transformation
matrix.setElement(1, 1,  cosAngle);
matrix.setElement(1, 2,  sinAngle);
matrix.setElement(2, 1, -sinAngle);
matrix.setElement(2, 2,  cosAngle);

// Apply rotation
transformation.multiply(matrix);

    

    


    
    

Rationale: Enhances readability by introducing white space between logical units. Each block is often introduced by a comment as indicated in the example above.

Put related classes in a single package.

Package together the classes that are related. For example in Java, the classes related to file writing is grouped in the package java.io and the classes which handle lists, maps etc are grouped in java.util package.

The ordering of import statements must be consistent.

Rationale: A consistent ordering of import statements makes it easier to browse the list and determine the dependencies when there are many imports.

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

import java.io.File;
import java.io.IOException;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;

import org.loadui.testfx.GuiTest;
import org.testfx.api.FxToolkit;

import com.google.common.io.Files;

import javafx.geometry.Bounds;
import javafx.geometry.Point2D;
import junit.framework.AssertionFailedError;

    

    


    
    

IDEs have support for auto-ordering import statements. However, note that the default orderings of different IDEs are not always the same. It is recommended that you and your team use the same IDE and stick to a consistent ordering.

Classes and Interfaces

Class and Interface declarations should be organized in the following manner:

1. Class/Interface documentation (Comments)
2. class or interface statement
3. Class (static) variables in the order public, protected, package (no access modifier), private
4. Instance variables in the order public, protected, package (no access modifier), private
5. Constructors
6. Methods (no specific order)

Rationale: Make code easy to navigate by making the location of each class element predictable.

Methods

Method modifiers should be given in the following order:

<access> static abstract synchronized <unusual> final native

<access> = public | protected | private
<unusual> = volatile | transient

    

    


    
    

The <access> modifier (if present) must be the first modifier.

public static double square(double a);

    

    


    
    

static public double square(double a);

    

    


    
    

Rationale: The most important point here is to keep the access modifier as the first modifier. The order is less important for the other modifiers , but it make sense to have a fixed convention.

Variables

Variables should be initialized where they are declared and they should be declared in the smallest scope possible.

int sum = 0;
for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        sum += i * j;
    }
}


    

    


    
    

int i, j, sum;
sum = 0;
for (i = 0; i < 10; i++) {
    for (j = 0; j < 10; j++) {
        sum += i * j;
    }
}

    

    


    
    

Rationale: This ensures that variables are valid at any time. Sometimes it is impossible to initialize a variable to a valid value where it is declared. In these cases it should be left uninitialized rather than initialized to some phony value.

Class variables should never be declared public unless the class is a data class with no behavior. This rule does not apply to constants.

Bad

public class Foo{

   public int bar;

}

    

    


    
    

Rationale: The concept of Java information hiding and encapsulation is violated by public variables. Use non-public variables and access functions instead.

Avoid unnecessary use of this with fields.

Use the this keyword only when a field is shadowed by a method or constructor parameter.

public User(String name) {
    this.name = name;
    ...
}


    

    


    
    

public User(String name) {
    // 'id' is not shadowed by any method parameters
    this.id = User.getNewId();
    ...
}

    

    


    
    

Rationale: to reduce unnecessary noise.

Write descriptive header comments for all public classes/methods.

You MUST write header comments for all classes, public methods. But they can be omitted for the following cases:
i. Getters/setters
ii. When overriding methods (provided the parent method's Javadoc applies exactly as is to the overridden method)

Rationale: public method are meant to be used by others and the users should not be forced to read the code of the method to understand its exact behavior. The code, even if it is self-explanatory, can only tell the reader HOW the code works, not WHAT the code is supposed to do.

All non-trivial private methods should carry header comments.

Rationale: Writing header comments will hep novice programmers to self-detect abstraction problems. e.g. If it is hard to describe the method succinctly, there is something wrong with the method abstraction.

Javadoc comments should have the following form:

/**
 * Returns lateral location of the specified position.
 * If the position is unset, NaN is returned.
 *
 * @param x X coordinate of position.
 * @param y Y coordinate of position.
 * @param zone Zone of position.
 * @return Lateral location.
 * @throws IllegalArgumentException If zone is <= 0.
 */
public double computeLocation(double x, double y, int zone)
        throws IllegalArgumentException {
    //...
}

    

    


    
    

Note in particular:

• The opening /** on a separate line.
• Write the first sentence as a short summary of the method, as Javadoc automatically places it in the method summary table (and index).
  • In method header comments, the first sentence should start in the form Returns ..., Sends ..., Adds ... etc. (not Return or Returning etc.)
• Subsequent * is aligned with the first one.
• Space after each *.
• Empty line between description and parameter section.
• Punctuation behind each parameter description.
• No blank line between the documentation block and the method/class.
• @return can be omitted if the method does not return anything or the return value is obvious from the rest of the comment.
• @params can be omitted if all parameters of a method have self-explanatory names or already explained in the main part of the comment i.e., when adding @params to the comment does not add any value. This means the comment will have @param for all its parameters, or none.
• When writing Javadocs for overridden methods, the @inheritDoc tag can be used to reuse the header comment from the parent method but with further modifications e.g., when the method has a slightly different behavior from the parent method.

Javadoc of class members can be specified on a single line as follows:

/** Number of connections to this database */
private int connectionCount;

    

    


    
    

Comments should be indented relative to their position in the code.

while (true) {
    // Do something
    something();
}

    

    


    
    

while (true) {
        // Do something
    something();
}

    

    


    
    

while (true) {
// Do something
    something();
}

    

    


    
    

Rationale: This is to avoid the comments from breaking the logical structure of the program.

Note that trailing comments such as the below are allowed as well.

    process('ABC'); // process a dummy String frst