An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions. The ThreadDeath error, though a "normal" condition, is also a subclass of Error because most applications should not try to catch it.
A method is not required to declare in its throws clause any subclasses of Error that might be thrown during the execution of the method but not caught, since these errors are abnormal conditions that should never occur.
java.lang.Object java.lang.Throwable java.lang.Error
The class Exception and its subclasses are a form of Throwable that indicates conditions that a reasonable application might want to catch.
java.lang.Object java.lang.Throwable java.lang.Exception
RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.
A method is not required to declare in its throws clause any subclasses of RuntimeException that might be thrown during the execution of the method but not caught.
java.lang.Object java.lang.Throwable java.lang.Exception java.lang.RuntimeException