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Joshua Bloch [Bloch 2008] suggests implementing a stop()
method explicitly such that it leaves the class in an unusable state beyond its lifetime. A private field within the class can signal whether the class is unusable. All the class methods must check this field prior to operating on the class. This is akin to the "initialized flag"–compliant solution discussed in OBJ11-J. Be wary of letting constructors throw exceptions. As always, a good place to call the termination logic is in the finally
block.
Exceptions
MET12-J-EX0: Finalizers may be used when working with native code because the garbage collector cannot reclaim memory used by code written in another language and because the lifetime of the object is often unknown. Again, the native process must not perform any critical jobs that require immediate resource deallocation.
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The ordering problem can be dangerous when dealing with native code. For example, if object A
references object B
(either directly or reflectively) and the latter gets finalized first, A
's finalizer may end up dereferencing dangling native pointers. To impose an explicit ordering on finalizers, make sure that B
remains reachable until A
's finalizer has concluded. This can be achieved by adding a reference to B
in some global state variable and removing it when A
's finalizer executes. An alternative is to use the java.lang.ref
references.
MET12-J-EX1: A class may use an empty final finalizer to prevent a finalizer attack, as specified in OBJ11-J. Be wary of letting constructors throw exceptions.
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