The extcheck command checks a specified JAR file for title and version conflicts with any extensions installed in the Java SE SDK. Before installing an extension, you can use this utility to see whether the same or a more recent version of the extension is already installed.
The extcheck command compares the Specification-title and Specification-version headers in the manifest of the targetfile.jar file against the corresponding headers in all JAR files currently installed in the extension directory. By default, the extension directory is jre/lib/ext on Oracle Solaris and \jre\lib\ext on Windows. The extcheck command compares version numbers in the same way as the java.lang.Package.isCompatibleWith method.
If no conflict is detected, then the return code is 0.
If the manifest of any JAR file in the extensions directory has the same Specification-title and the same or a newer Specification-version number, then a non-zero error code is returned. A non-zero error code is also returned when targetfile.jar does not have the Specification-title or Specification-version attributes in its manifest file.