End users can modify JDK 5.0

Sun has decided to use a new license for the JDK called the Java Internal Use License,
as Ray Gans reported in Java Internal Use License (JIUL) released for JDK 5.0. The
license lets end users fix any critical bug in the JDK that could affect deployed Java applications. JDK 5.0 was released under this new
license.

End-users of Sun’s implementations of J2SE 5.0 now have the ability under 
the JIUL to fix any critical issue in the code that adversely affects their business operations. 
In addition, Sun will waive the commercial requirement to pass the Technology 
Compatibility Kit (TCK) for J2SE (a.k.a. the JCK) as long as all code changes 
are made with diligence to assure the resulting implementation remains true 
to the specification and that its use is restricted to the licensee’s internal 
business or organization.