Why are some exceptions in Java not caught by catch (Exception ex)
? This is code is completely failing out with an unhandled exception. (Java Version 1.4).
public static void main(String[] args) {
try {
//Code ...
} catch (Exception ex) {
System.err.println("Caught Exception");
ex.printStackTrace();
exitCode = app.FAILURE_EXIT_CODE;
}
finally {
app.shutdown();
}
System.exit(exitCode);
}
I get a Exception in thread "main" java.lang.NoSuchMethodError
But this works
public static void main(String[] args) {
int exitCode = app.SUCCESS_EXIT_CODE;
try {
//Code ...
} catch (java.lang.NoSuchMethodError mex){
System.err.println("Caught NoSuchMethodError");
mex.printStackTrace();
exitCode = app.FAILURE_EXIT_CODE;
} catch (Exception ex) {
System.err.println("Caught Exception");
ex.printStackTrace();
exitCode = app.FAILURE_EXIT_CODE;
}
finally {
app.shutdown();
}
System.exit(exitCode);
}
I get Caught NoSuchMethodError java.lang.NoSuchMethodError:
I thought catching exceptions would catch all exceptions? How can I catch all exceptions in java?
Because some exceptions don't derive from Exception
- e.g. Throwable
and Error
.
Basically the type hierarchy is:
Object
|
Throwable
/ \
Exception Error
Only Throwables
and derived classes can be thrown, so if you catch Throwable
, that really will catch everything.
Throwable
, Exception
and any exception deriving from Exception
other than those derived from RuntimeException
count as checked exceptions - they're the ones that you have to declare you'll throw, or catch if you call something that throws them.
All told, the Java exception hierarchy is a bit of a mess...