In 2013, Oracle announced the Java SE - Change in Version Numbering Scheme. The announcement stated that Limited Update releases (those "that include new functionality and non-security fixes") and Critical Patch Updates (CPUs) [those "that only include fixes for security vulnerabilities"] would be released with specific version number schemes. In particular, Limited Use Releases would have version numbers with multiples of 20 while Critical Patch Updates would have version numbers that are multiples of 5 and come after the latest Limited Use Release version number. The purpose of this scheme change was to allow room for versions with numbers between these, which allows Oracle "to insert releases – for example security alerts or support releases, should that become necessary - without having to renumber later releases."
Yesterday's announcement ("Java CPU and PSU Releases Explained") states, "Starting with the release of Java SE 7 Update 71 (Java SE 7u71) in October 2014, Oracle will release a Critical Patch Update (CPU) at the same time as a corresponding Patch Set Update (PSU) for Java SE 7." This announcement explains the difference between a CPU and a PSU:
|Critical Patch Update||CPU||"Fixes to security vulnerabilities and critical bug fixes."||Minimum recommended for everyone.|
|Patch Set Update||PSU||"All fixes in the corresponding CPU" and "additional non-critical fixes."||Recommended only for those needing bugs fixed by PSU additional fixes.|
Yesterday's announcement states that PSU releases (which are really CPU+ releases) will be released along with their corresponding CPU releases. Because the additional fixes that a PSU release contains beyond what's in the CPU release are expected to be part of the next CPU release, developers are encouraged to experiment with PSU releases to ensure that coming CPU features work well for them.