I would like to change some current interface methods in Commons RNG to have a default implementation. This is detected as not allowed by the current japicmp settings in commons parent. I think the settings should be updated.
The default settings for japicmp state that default methods introduced into an interface break binary (and source) compatibility. This is entry METHOD_NEW_DEFAULT in the japicmp-maven-plugin documentation here [1]. This is not correct (and is the reason for default methods in interfaces) and was fixed in commons parent in commit d5d3a1b [2]. Changing an existing method in an interface to have a default implementation is also listed as not compatible in japicmp (entry METHOD_ABSTRACT_NOW_DEFAULT). However I cannot prove that this does break binary (or functional) compatibility. I've tested execution of classes compiled against an old version of the interface when the classpath includes a new version with a default implementation. It all runs as expected, i.e. existing implementations of interface methods are invoked. I ran some other tools listed on the japicmp page against the code where one interface method has been changed from abstract to default. Java API Compliance Checker [3] revapi [4] If I do something wrong such as removing an interface method then the tools list compatibility as broken. If I add a default implementation to an interface method both these tools do not raise an error. The change is reported by the Java API Compliance Checker and is listed as compatible. However I cannot get revapi to report that the interface methods now have a default implementation. The revapi check is Method Now Default and is listed as a transparent change [5]. The omission from the report may be due to some settings I did not find in the maven plugin. I suggest updating commons parent to allow METHOD_ABSTRACT_NOW_DEFAULT to be a non-breaking change. Alex [1] https://siom79.github.io/japicmp/MavenPlugin.html [2] https://gitbox.apache.org/repos/asf?p=commons-parent.git;a=commit;h=d5d3a1bcb03cf3c2bb50e66786ce73e6779fa62d [3] http://ispras.linuxbase.org/index.php/Java_API_Compliance_Checker [4] https://revapi.org/revapi-site/main/index.html [5] https://revapi.org/revapi-java/0.26.1/differences.html#java.method.nowDefault
