Why can companies charge money for their JDK Version despite the GNU GPL v2 of OpenJDK? : <p>OpenJDK is released under the GNU General Public License v2.0 with a classpath exception. If you modify software under such license, you are obliged to release it under the GPL as well. 
So how come e.g. IBM can charge you for their modified version of the OpenJDK, which mostly includes bugfixes and minor optimizations by changing the existing OpenJDK (which means this doesn't fall under the classpath exception)? Don't they have to release it under the GPL as well which would make it free to use?</p>

<p>The only way I could explain this is, that they release the bug fixes and optimizations to OpenJDK delayed to their payed version, but I didn't find any reference stating this to be allowed.</p>
