Java Coding style

  • We use the Java Coding Style. Quick summary:

    • FirstLetterUpperCase for class names.

    • camelCase for method and variable names.

    • One declaration per line:

      int x, y; // this is BAD!
      int a;    // split it over
      int b;    // two lines
  • Braces should be placed like so (generally, opening braces on same line, closing braces on a new line):

    public void func(int arg) {
        if (arg != 0) {
            while (arg > 0) {
        } else {
  • Places we differ from the Java coding style:

    • Start class variable names with ‘m’ prefix (e.g. mSomeClassVariable) and static variables with ‘s’ prefix (e.g. sSomeStaticVariable)

    • import statements:

      • Do not use wildcard imports like `import java.util.*;`

      • Organize imports by blocks separated by empty line: org.mozilla.*, android.*, com.*, net.*, org.*, then java.* This is basically what Android Studio does by default, except that we place org.mozilla.* at the front - please adjust Settings -> Editor -> Code Style -> Java -> Imports accordingly.

      • Within each import block, alphabetize import names with uppercase before lowercase. For example, com.example.Foo is before

    • 4-space indents.

    • Spaces, not tabs.

    • Don’t restrict yourself to 80-character lines. Google’s Android style guide suggests 100-character lines, which is also the default setting in Android Studio. Java code tends to be long horizontally, so use appropriate judgement when wrapping. Avoid deep indents on wrapping. Note that aligning the wrapped part of a line, with some previous part of the line (rather than just using a fixed indent), may require shifting the code every time the line changes, resulting in spurious whitespace changes.

  • For additional specifics on Firefox for Android, see the Coding Style guide for Firefox on Android.

  • The Android Coding Style has some useful guidelines too.