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| Copyright 1999 Sams Publishing |
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| Understanding Thread Group Security |
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| The checkAccess() method of ThreadGroup is called internally by many of the other ThreadGroup methods . It checks to see if a SecurityManager exists for a VM. By default, applications do not have a SecurityManager installed. Applets, on the other hand, might ave one. |
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| If a SecurityManager exists and it determines that a particular thread is not permitted to take an action, it throws a SecurityException . SecurityException is a subclass of RuntimeException , so try/catch blocks are typically not used. If no SecurityManager is installed, or if the SecurityManager approves of the access, checkAccess() silently returns. |
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| A full discussion of security in Java is beyond the scope of this book. You just need to be aware that a SecurityException might be thrown from most of the methods of ThreadGroup . If you are writing an application, you can usually safely ignore these checkAccess() issues. |
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