/java-style-guide

The official Java style guide for raywenderlich.com

Primary LanguageShell

The Official raywenderlich.com Java Style Guide

This style guide is different from other you may see, because the focus is centered on readability for print and the web. We created this style guide to keep the code in our tutorials consistent.

Our overarching goals are conciseness, readability and simplicity.

You should also check out out Swift and Objective-C style guides too.

Inspiration

This style-guide is somewhat of a mash-up between the existing Java language style guides, and a tutorial-readability focused Swift style-guide. The language guidance is drawn from the Android contributors style guide and the Google Java Style Guide. Alterations to support additional readability in tutorials were inspired by the raywenderlich.com Swift style guide.

Android Studio Coding Style

It is possible to get Android Studio to adhere to these style guidelines, via a rather complex sequence of menus. To make it easier, we've provided a coding style that can be imported into Android Studio.

First, clone this repository and run install.sh.

Then, open Android Studio. To set this codestyle as the default, select File > Other Settings > Default Settings...:

Default Settings

In Editor > Code Style, choose the Scheme to be raywenderlich.com:

Setting the Scheme

From now on, projects you create should follow the correct style guidelines.

Table of Contents

Nomenclature

On the whole, naming should follow Java standards.

Packages

Package names are all lower-case, multiple words concatenated together, without hypens or underscores:

BAD:

com.RayWenderlich.funky_widget

GOOD:

com.raywenderlich.funkywidget

Classes & Interfaces

Written in UpperCamelCase. For example RadialSlider.

Methods

Written in lowerCamelCase. For example setValue.

Fields

Written in lowerCamelCase.

Static fields should be written in uppercase, with an underscore separating words:

public static final int THE_ANSWER = 42;

As distasteful as it is, field naming should follow the Android source code naming conventions:

  • Non-public, non-static field names start with an m.
  • Static field names start with an s.

For example:

public class MyClass {
  public static final int SOME_CONSTANT = 42;
  public int publicField;
  private static MyClass sSingleton;
  int mPackagePrivate;
  private int mPrivate;
  protected int mProtected;
}

Note: You can set Android Studio to follow this convention. See this SO link for details http://stackoverflow.com/questions/22732722/intellij-android-studio-member-variable-prefix

Variables & Parameters

Written in lowerCamelCase.

Single character values to be avoided except for temporary looping variables.

Misc

In code, acronyms should be treated as words. For example:

BAD:

XMLHTTPRequest
String URL
findPostByID

GOOD:

XmlHttpRequest
String url
findPostById

Declarations

Access Level Modifiers

Access level modifiers should be explicitly defined for classes, methods and member variables.

Fields & Variables

Prefer single declaration per line.

BAD:

String username, twitterHandle;

GOOD:

String username;
String twitterHandle;

Classes

Exactly one class per source file, although inner classes are encouraged where scoping appropriate.

Enum Classes

Enum classes should be avoided where possible, due to a large memory overhead. Static constants are preferred. See http://developer.android.com/training/articles/memory.html#Overhead for further details.

Enum classes without methods may be formatted without line-breaks, as follows:

private enum CompassDirection { EAST, NORTH, WEST, SOUTH }

Spacing

Spacing is especially important in raywenderlich.com code, as code needs to be easily readable as part of the tutorial. Java does not lend itself well to this.

Indentation

Indentation is using spaces - never tabs.

Blocks

Indentation for blocks uses 2 spaces (not the default 4):

BAD:

for (int i = 0; i < 10; i++) {
    Log.i(TAG, "index=" + i);
}

GOOD:

for (int i = 0; i < 10; i++) {
  Log.i(TAG, "index=" + i);
}

Line Wraps

Indentation for line wraps should use 4 spaces (not the default 8):

BAD:

CoolUiWidget widget =
        someIncrediblyLongExpression(that, reallyWouldNotFit, on, aSingle, line);

GOOD:

CoolUiWidget widget =
    someIncrediblyLongExpression(that, reallyWouldNotFit, on, aSingle, line);

Line Length

Lines should be no longer than 100 characters long.

Vertical Spacing

There should be exactly one blank line between methods to aid in visual clarity and organization. Whitespace within methods should separate functionality, but having too many sections in a method often means you should refactor into several methods.

Getters & Setters

For external access to fields in classes, getters and setters are preferred to direct access of the fields. Fields should rarely be public.

However, it is encouraged to use the field directly when accessing internally (i.e. from inside the class). This is a performance optimization recommended by Google: http://developer.android.com/training/articles/perf-tips.html#GettersSetters

Brace Style

Only trailing closing-braces are awarded their own line. All others appear the same line as preceding code:

BAD:

class MyClass
{
  void doSomething()
  {
    if (someTest)
    {
      // ...
    }
    else
    {
      // ...
    }
  }
}

GOOD:

class MyClass {
  void doSomething() {
    if (someTest) {
      // ...
    } else {
      // ...
    }
  }
}

Conditional statements are always required to be enclosed with braces, irrespective of the number of lines required.

BAD:

if (someTest)
  doSomething();
if (someTest) doSomethingElse();

GOOD:

if (someTest) {
  doSomething();
}
if (someTest) { doSomethingElse(); }

Switch Statements

Switch statements fall-through by default, but this can be unintuitive. If you require this behavior, comment it.

Alway include the default case.

BAD:

switch (anInput) {
  case 1:
    doSomethingForCaseOne();
  case 2:
    doSomethingForCaseOneOrTwo();
    break;
  case 3:
    doSomethingForCaseOneOrThree();
    break;
}

GOOD:

switch (anInput) {
  case 1:
    doSomethingForCaseOne();
    // fall through
  case 2:
    doSomethingForCaseOneOrTwo();
    break;
  case 3:
    doSomethingForCaseOneOrThree();
    break;
  default:
    break;
}

Annotations

Standard annotations should be used - in particular @Override. This should appear the line before the function declaration.

BAD:

protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
}

GOOD:

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
}

XML Guidance

Since Android uses XML extensively in addition to Java, we have some rules specific to XML.

XML File Names

View-based XML files should be prefixed with the type of view that they represent.

BAD:

  • login.xml
  • main_screen.xml
  • rounded_edges_button.xml

GOOD:

  • activity_login.xml
  • fragment_main_screen.xml
  • button_rounded_edges.xml

Indentation

Similarly to Java, indentation should be two characters.

Use Context-Specific XML Files

Wherever possible XML resource files should be used:

  • Strings => res/values/strings.xml
  • Styles => res/values/styles.xml
  • Colors => res/color/colors.xml
  • Animations => res/anim/
  • Drawable => res/drawable

XML Attribute Ordering

Where appropriate, XML attributes should appear in the following order:

  • id attribute
  • layout_* attributes
  • style attributes such as gravity or textColor
  • value attributes such as text or src

Within each of these groups, the attributes should be ordered alphabetically.

Language

Use US English spelling.

BAD:

String colour = "red";

GOOD:

String color = "red";

Copyright Statement

The following copyright statement should be included at the top of every source file:

/*
 * Copyright (c) 2017 Razeware LLC
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * Notwithstanding the foregoing, you may not use, copy, modify, merge, publish, 
 * distribute, sublicense, create a derivative work, and/or sell copies of the 
 * Software in any work that is designed, intended, or marketed for pedagogical or 
 * instructional purposes related to programming, coding, application development, 
 * or information technology.  Permission for such use, copying, modification,
 * merger, publication, distribution, sublicensing, creation of derivative works, 
 * or sale is expressly withheld.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

Smiley Face

Smiley faces are a very prominent style feature of the raywenderlich.com site! It is very important to have the correct smile signifying the immense amount of happiness and excitement for the coding topic. The closing square bracket ] is used because it represents the largest smile able to be captured using ASCII art. A closing parenthesis ) creates a half-hearted smile, and thus is not preferred.

Bad:

:)

Good:

:]

Credits

This style guide is a collaborative effort from the most stylish raywenderlich.com team members: