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This compliant solution does not violate CON04-J. Use the Synchronize using an internal private lock object idiom instead of the object's intrinsic lock because the accessibility of the class is package-private which is allowable when untrusted code cannot infiltrate the package.
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This is the preferred choice when untrusted code can obtain the intrinsic lock of the class object (CON04-J. Use the Synchronize using an internal private lock object idiom instead of the object's intrinsic lock).
Exceptions
EX1: If the subclass implements block synchronization instead of method synchronization, it is likely that thread-safety has been accounted for. This condition should be sufficiently documented.
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