# Java Coding style

- We use the [Java Coding
  Style](https://www.oracle.com/technetwork/java/codeconvtoc-136057.html).
  Quick summary:

  - FirstLetterUpperCase for class names.

  - camelCase for method and variable names.

  - One declaration per line:

    ```java
    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):

  ```java
  public void func(int arg) {
      if (arg != 0) {
          while (arg > 0) {
              arg--;
          }
      } else {
          arg++;
      }
  }
  ```

- 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 `com.example.bar`

  - 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.

- NOTE: Geckoview uses the [Google Java Style](https://google.github.io/styleguide/javaguide.html) instead of the Java Coding Style.

- However, the [Android Coding
  Style Documentation](https://source.android.com/source/code-style.html) has some
  useful guidelines too.