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We use the following code conventions for Java and JavaScript.


The OpenTripPlanner Java code style is revised in OTP2. We use the Google Java style guide, with a few modifications. Here is the original Google style guide:

IntellJ Code Style formatter

If you use IntelliJ, import the provided intellij-code-style.xml. Open the Preferences from the menu and select Editor > Code Style. Then import the code-style xml document. Configure Scheme using Import Scheme > IntelliJ IDEA code style XML.

Note that the IntelliJ formatter will not always format the code according to the coding standard. It struggle to do the line breaks properly. Hence, use it to format new code and to rearrange members, then manually fix any mistakes.

Other IDEs

We do not have support for other IDEs at the moment. If you use another editor and make one please feel free to share it.

Code Style

Our style differs in the following ways from the Google guide. Each point references the section of the original document that is modified.

  • 4.5.1 We apply the same line breaking rules to parentheses as to curly braces. Any time the contents of the parentheses are not all placed on one line, we insert a line break after the opening paren, and place the closing one at the beginning of a new line.

    int value = calculateSomeValue(
    // Also Ok
    int value = calculateSomeValue(
        arg1, arg2, arg3 
    // Avoid this
    int value = calculateSomeValue(arg1,
        arg2, arg3 
    // and this
    int value = calculateSomeValue(
        arg1, arg2, arg3) 

  • 4.6.1 We insert double empty lines before comments that introduce the highest level groupings of methods or fields within a class, for example /* private methods */, /* symbolic constants */.

    public foo() { 
    /* private methods */
    private bar() ...

  • 4.8.3 the final example is not allowed. All opening brackets or parens should be on the same line as the identifier or other construct that they follow.
  • 4.8.5 All annotations on classes, fields, and methods should always have a newline after the last annotation, i.e. they should not appear on the same line as the identifier they annotate, and should only appear on the same line as other annotations. Series of multiple annotations may each appear on a separate line, or may all be grouped together on the same line.
  • On multi-line /* ... */ comments we do not begin the intermediate lines with asterisks *.
  • 5.2.8 We only use single capital letters (single characters) for generic type parameters.
  • 7.2 We do not begin Javadoc with summary fragments. This is because will no longer generate and publish Javadoc pages, the Javadoc will only be used within IDEs.
  • 7.3.1 The item in the original document implies that trivial Javadoc like /** Returns the canonical name. */ should still be included. There is almost always something more to explain to someone who is seeing this method or class for the first time.

Notes on breaking lines

The eye scan the code much faster if there is less need of horizontal movement, so formatting the code becomes a balance on how long the lies should be and how to break it. Try to brake the code at the outer-most scope aligning expressions with the same scope. Consider to chop down all expressions with the same scope and indent them, do not align code further to the right than the indentation margin.

  // Conider this code:
  xxxx xxx = xxx + xxx * xxx - ( x.xxxx().xx().xxx() - xxx ) / xxx;

  // Break tha line as every operator, pharenphasis and method chanin.
  // This is a bit extrem, but illustrates the correct way to break the lines.
  xxxx xxx 
      = xxx 
          * xxx 
              - xxx 
          / xxx

  // Prefered compromize
  xxxx xxx = xxx + xxx * xxx 
      - ( x.xxxx().xx().xxx() - xxx ) / xxx

  // or 
  xxxx xxx 
      = xxx + xxx * xxx 
      - ( 
          - xxx 
      ) / xxx
  // Right alignment not allowed
  xxxx xxx = xxx 
           + xxx * xxx; 

  // use indentation margin instead
  xxxx xxx = xxx
      + xxx * xxx; 

Sorting class members

Some of the classes in OTP have a lot of fields and methods. Keeping members sorted reduce the merge conflicts. Adding fields and methods to the end of the list will cause merge conflicts more often than inserting methods and fields in an ordered list. Fields and methods can be sorted in "feature" sections or alphabetically, but stick to it and respect it when adding new methods and fields.

The provided formatter will group class members in this order:

  1. Getter and Setter methods are kept together
  2. Overridden methods are kept together
  3. Dependent methods are sorted in a breadth-first order.
  4. Members are sorted like this:
    1. static final fields
    2. static fields
    3. static initializer
    4. final fields
    5. fields
    6. class initializer (avoid using it)
    7. Constructor
    8. static methods
    9. static getter and setters
    10. methods
    11. getter and setters
    12. enums
    13. interfaces
    14. static classes
    15. classes
  5. Each section of members are sorted by visibility:
    1. ´public´
    2. package private
    3. ´protected´
    4. ´private´

JavaDoc Guidlines

What to put in Javadoc: - On methods: - Side effects on instance state (is it a pure function) - Contract of the method - Input domain for which the logic is designed - Range of outputs produced from valid inputs - Is behavior undefined or will fail when conditions are not met - Are null values allowed as inputs - Will null values occur as outputs (what do they mean) - Invariants that hold if the preconditions are met - Concurrency - Is method thread-safe - Usage constraints for multi-threaded use - On classes: - Initialization and teardown process - Can instance be reused for multiple operations, or should it be discarded - Is it immutable or should anything be treated as immutable - Is it a utility class of static methods that should not be instantiated


As of #206, we follow Crockford's JavaScript code conventions. Further guidelines include:

  • All .js source files should contain one class only
  • Capitalize the class name, as well as the source file name (a la Java)
  • Include the namespace definition in each and every file: otp.namespace("otp.configure");
  • Include a class comment. For example,
 * Configure Class
 * Purpose is to allow a generic configuration object to be read via AJAX/JSON, and inserted into an
 * Ext Store
 * The implementation is TriMet route map specific...but replacing ConfigureStore object (or member
 * variables) with another implementation, will give this widget flexibility for other uses beyond 
 * the iMap.
 * @class

Note: There is still a lot of code following other style conventions, but please adhere to consistent style when you write new code, and help clean up and reformat code as you refactor.