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Unchecked exception classes such as Error and its subclasses are not subject to compile-time checking not only because it is tedious to account for all exceptional conditions , but also and because recovery is generally difficult. However, even when recovery is impossible, the Java Virtual Machine (JVM) allows a graceful exit and a chance to at least log the error. This is made possible by using a try-catch block that catches Throwable. Also, when code must avoid leaking potentially sensitive information, catching Throwable is permitted. In all other cases, catching Throwable is not recommended. Where cleanup operations such as releasing system resources are possible, code should use a finally block within which the resources are released or should use a try-with-resources statement.
Catching Throwable is forbidden by rule ERR08-J. Do not catch NullPointerException or any of its ancestors, but is permitted when filtering exceptions by the exception ERR08-EX0 in that rule.
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Note that the Forward to handler code must operate correctly in very constrained memory conditions , because the stack or heap may be nearly exhausted. In such a scenario, one useful technique would be for the program to initially reserve memory specifically to be used by an out-of-memory exception handler.
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In the event of actually running out of memory, it is likely that some program data will be in an inconsistent state. Consequently, it might be best to restart the process. If an attempt is made to carry on, reducing the number of threads , or just simply cycling them , may be a good idea because threads often leak memory.
The methods
Thread.setUncaughtExceptionHandler()andThreadGroup.uncaughtException()can be used to help deal with anOutOfMemoryErrorin threads.