Indent using tabs, not spaces.
Rationale: using tabs does not rely on fixed-width fonts, allows users to define their indentation size per tab either in spaces or even in cm or px, and they consume less characters.
Text files must end with a line separator.
See CheckStyle configuration.
See CheckStyle configuration.
Exception messages must be phrases and not sentences, using sentence case. They must start with a lowercase letter and not end with a punctuation mark.
Log messages must be sentences using sentence case. They must start with an uppercase letter and end with a punctuation mark.
Use "directory" instead of "folder".
Use perfect antonyms. For example, use "log in" and "log out", not "log in" and "log off" (the antonym of "off" being "on").
Use "log in/out" instead of "log on/off" or "sign in/out".
Suffix directories (or any non-leaf paths) with a slash so that it is clear from the path name that it's a directory. For example use "http://my.site.com/" instead of "http://my.site.com".
Unit test classes must end with Test.
Integration test classes must end with IntegrationTest.
Test classes and methods must be package-private by default. They may be public, but only for a specific reason.
Test methods must not start with test.
The @Test annotation alone is clear enough,
and prefixing every method with test clutters screen real estate that needs to be mentally ignored by the reader.
Test methods must be camel-cased as regular methods, and must not contain spaces. A good test method name completes the phrase "test that ...".
Tests must always load resources from the class path.
Never assume resources are files.
This ensures that tests can be run from within a *-tests.jar or that test resources from dependencies can be reused.
Test resources must reside in the directory corresponding to the package and class the resource is for. Resources common to tests may be in the package root. Resources specific to a particular test must be in a subdirectory
Release versions must only depend on other release versions, never on snapshots.
This includes parent projects, which are considered a form of dependencies.
Snapshot versions may depend on snapshot versions (also for parents).
This is enforced by the maven-enforcer-plugin.
All code must be covered 100% with unit tests by default.
This is enforced by the jacoco-maven-plugin.