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Android Code Style

Code guidelines used when developing Android applications.

Naming Convention

Class Files

Class names are in UpperCamelCase.

Component Class Name
Activity LoginActivity
Fragment ProfileFragment
Service BroadcastService
Adapter ContactAdapter
Holder ContactHolder
Dialog EditTextDialog

Resource Files

Resource names are in lowercase_underscore.

Layouts

Layout names should specify the component type follow by the class name defined.

Component Class Name Layout Name
Activity LoginActivity activity_login
Fragment ProfileFragment fragment_profile
Adapter -- item_contact
Dialog EditTextDialog dialog_edit_text

Strings

String names should specify the type of string follow by the use of string.

Prefix Description
error_ Error message
msg_ Regular information message
title_ Title e.g. Activity or dialog title
action_ An action such as save, cancel, ok etc.

Drawables

Drawable names should specify the type of drawable follow by the use of drawable.

Drawable Type Prefix Drawable Name
Background image (png, jpeg) bg_ bg_article
Button with background btn_bg_ btn_bg_purple
Button with border btn_bd_ btn_bd_purple
Button with radius 3 btn_rd_ btn_rd_3
Button with background, border and radius btn_bg_bd_rd btn_bg_white_bd_purple_rd
Icon ic_ ic_launcher

Resources ID

ID names should specify type of element follow by use of the content.

Element Prefix
Layouts (e.g. LinearLayout) layout_
TextView text_
EditText edit_
ImageView image_
Button button_
FloatingActionButton fab_
ProgressBar progress_

Android Java Styles

Fields Naming

  • Constants (static final fields) are ALL_CAPS_WITH_UNDERSCORES.
  • Private/protected, non-static field names start with m.
  • Private/protected, static field names start with s.
  • Other fields start with a lower case letter.
public class MainActivity {
    public static final String TITLE_DIALOG = "title";
    
    public int id;
    
    private static int sVariable;
    private int mVariable;
}

Constants Naming

Element Prefix
SharedPreferences PREF_
Bundle BUNDLE_
Intent Extra EXTRA_ 
private static final String PREF_EMAIL = "PREF_EMAIL";
private static final String BUNDLE_EMAIL = "BUNDLE_EMAIL";
private static final String EXTRA_EMAIL = "com.myapp.extras.EXTRA_EMAIL";

Braces

Braces shall be on the same line as the code before them.

if(isTrue) {
    // ...
} else {
    // ...
}

Use braces even if the if condition and body fit on one line!

if(isTrue) {
    // ...
}

Variables Ordering

  1. Constants
  2. UI variables (TextView etc)
  3. Other variables (String, int)
public class MainActivity extends Activity {

    private static final String TAG = MainActivity.class.getSimpleName();
    
    private EditText mEditTextEmail;
    
    private String mEmail;
}

Methods Ordering

  1. Constructors
  2. Override methods and callbacks (public or private)
  3. Public methods
  4. Private methods
  5. Inner classes or interfaces

Line Length Limit

Each code line should not exceed 100 characters.

Long Method Chain

Picasso.with(context)
        .load("http://google.com/hello.jpg")
        .into(imageView);

Long Method Paramters

loadPicture(context,
        "http://google.com/hello.jpg",
        mImageViewProfilePicture,
        clickListener,
        "Title of the picture");

Logging

Use Log to print out error messages or other information that may be useful for developers to identify issues. VERBOSE and DEBUG logs must be disabled on release builds. Leave INFORMATION, WARNING and ERROR logs enabled only if they are not leaking private information such as email addresses.

To only show logs on debug builds:

if (BuildConfig.DEBUG) {
     Log.d(TAG, "Email: " + email);
}

Verbose

Show all log messages (default).

Log.v(String tag, String msg)

Debug

Show debug log messages that are useful during development, such as logging the exact flow of your program.

Log.d(String tag, String msg)

Information

Show expected log messages for regular usage, as well as the message levels lower in this list.

Log.i(String tag, String msg)

Warning

Show possible issues that are not yet errors.

Log.i(String tag, String msg)

Error

Show issues that have caused errors, such as in a catch statement.

Log.e(String tag, String msg)

Use class name as tag and define it as a static final field at the top of the file. For example:

public class MainActivity {
    private static final String TAG = MainActivity.class.getSimpleName();

    public method() {
        Log.e(TAG, "Error message");
    }
}

References