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I find Java's exception hierarchy confusing. Throwable is divided into Error and Exception, and RuntimeException inherits from Exception.
Error is an unchecked exception. Why doesn't Error inherit from RuntimeException then?
Exception is a checked exception. RuntimeException is an unchecked exception, yet it inherits from Exception. Doesn't this violate the Liskov-Substitution-Principle?
Wouldn't it make more sense if Throwable were divided into Exception (checked) and RuntimeException (unchecked), and Error would inherit from RuntimeExeption?
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The class at the top of the exception class hierarchy is the Throwable class, which is a direct subclass of the Object class. Throwable has two direct subclasses - Exception and Error. The Exception class is used for exception conditions that the application may need to handle.
An exception is thrown for one of three reasons: An abnormal execution condition was synchronously detected by the Java virtual machine. Such conditions arise because: evaluation of an expression violates the normal semantics of the language, such as an integer divide by zero, as summarized in §15.6.
The hierarchy of Exceptions in the Java programming language begins with the Throwable class – which comes from the Object class and is its direct subclasswhileThe Exception class presents all This Throwable class further branches into two subclasses – Error and Exception.
The Python exception class hierarchy consists of a few dozen different exceptions spread across a handful of important base class types. As with most programming languages, errors occur within a Python application when something unexpected goes wrong.
Chained Exception helps to identify a situation in which one exception causes another Exception in an application.
I find Java's exception hierarchy confusing. Throwable is divided into Error and Exception, and RuntimeException inherits from Exception.
A Throwable is anything that can be used to unwind the call stack. This should include some VM level fault (flagged by an Error) and something application specific (flagged by an Exception)
Erroris an unchecked exception. Why doesn't Error inherit from RuntimeException then?
Simply because Errors are not Exceptions. There wouldn't be any point in actually "catching" an Error. For eg. What would you do after catching an OutOfMemoryError. Errors are meant to flag something seriously happened at the VM level which is not necessarily handle-able by the programmer
Exception is a checked exception. RuntimeException is an unchecked exception, yet it inherits from Exception. Doesn't this violate the Liskov-Substitution-Principle?
Not really. What the implementors were trying to say was that Exceptions MUST always be checked. Your code will be cleaner if all your methods declare what sort of application/library Exceptions they throw. RuntimeExceptions should only be thrown in case of more general / dynamic situations such as a NullPointerException where the developer might not have coded for the case but is a serious bug which is not exactly something mentioned in the application spec.
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