Development Guidelines

How your code should look like

• make sure the code is Java 8 compatible
• Document your code using inline comments and javadoc. Many people will thank you :)
• Try to avoid public fields
• JOSM has a lot of helper methods in the Utils, GuiUtils, Geometry ... classes. Use them if you need
• Check parameters. You can use Objects.requireNonNull.
• Don't write for performance - write for readability. Use Streams, Functions and other Java 8 features if they make the code more readable.

Threading / Locking

• JOSM uses various locking mechanisms, depending on the object.
• The data sets are protected by a RW lock. Some methods do not automatically lock for performance reasons. Make sure to acquire the locks required for your changes.
• GUI components should only be modified in the EDT thread
• Prefer to use SwingUtils.invokeLater if you need to run anything on the UI thread
• Many listeners already run in the EDT thread (layer changes) or have a central manager that allows you to register listeners that run in EDT (dataset changes, selection changes).

How your formatting should look like

• make sure there is no trailing white space
• don't use multiple consecutive empty lines
• JOSM uses 4 characters indentation and no tab stops. If you use Notepad++ you can change the default indentation in the "Preferences" -> "Language" -> "Tab Settings" -> check "Replace by spaces" (this is permanent) or with the "change indentation settings" button in the toolbar (this is a temopary setting and requires the plugin "Customize Toolbar").
• add curly brackets for each if, unless it is followed by return (or maybe throw)
• You should use checkstyle before patch/commit: ant checkstyle and check checkstyle-josm.xml; if you find running checkstyle slow for all files, run for changed files only:

    # make sure build2 dir exists, if it does not run 'ant checkstyle-compile' before
  
    svn diff --summarize | awk '{ print $2 }' | grep "^[a-z]" | xargs \
      java -classpath "build2:tools/checkstyle/checkstyle-all.jar" \
        com.puppycrawl.tools.checkstyle.Main -c tools/checkstyle/josm_checks.xml
    # or
    git diff --name-only | xargs \
      java -classpath "build2:tools/checkstyle/checkstyle-all.jar" \
        com.puppycrawl.tools.checkstyle.Main -c tools/checkstyle/josm_checks.xml
  

How your javadoc should look like

• The ​Oracle Javadoc style guide is used as the base guide
• @since is used for public classes and methods (visible to plugin developers) with the JOSM revision that introduced the element. Example: @since 5408
  • @since is updated / added when a public method signature changes or if a class is renamed.
  • @since can be omitted for public methods and fields introduced at the same time as the class, provided they do not have changed and the class is correctly documented.
  • There can be multiple @since tags, e.g. for adding interfaces to a class. The reason for those tags should be added Example: @since 12345 @FunctionalIterface was added
  • If you submit a patch and don't know the revision, add @since xxx any way. It can then be replaced when merging your patch.
• @throws is preferred to @exception
• check your changes before patch/commit by generating javadoc: ant javadoc, browse output messages; if you find running javadoc slow for all files, run for changed files only:

    svn diff --summarize | awk '{ print $2 }' | xargs javadoc -d javadoc
    # or
    git diff --name-only | xargs javadoc -d javadoc

Configuring Eclipse

Internationalization

• make sure you use tr(...) for all localized strings

  import import static org.openstreetmap.josm.tools.I18n.tr;
  
  // use tr(...) for exception messages
  //
  throw new Exception(tr("error message always in tr()"));
  
  // use tr(...) for labels, title, tooltip texts and the like
  //
  new JLabel(tr("Label always in tr()"));
  
  // etc.
  

• never assemble localized messages with +. Use format placeholders instead.

DONT new JLabel(tr("My Label " + labelId));

DO new JLabel(tr("My Label {0}",labelId));

Only exception: + can be used to break long lines of non-variable texts.

• When using apostrophe, the following rules apply:

For all tr the apostrophe is special. (Like backslash in C)
It needs to be escaped by another apostrophe:

new JButton(tr("Don''t press me more than {0} times!", n))

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