Declaration of Throws for Generic Exception

Description

Declaring a method to throw Exception or Throwable makes it difficult for callers to perform proper error handling and error recovery. Java's exception mechanism, for example, is set up to make it easy for callers to anticipate what can go wrong and write code to handle each specific exceptional circumstance. Declaring that a method throws a generic form of exception defeats this system.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following method throws three types of exceptions.

public void doExchange() throws IOException, InvocationTargetException, SQLException {
  ...
}

While it might seem tidier to write

public void doExchange() throws Exception {
  ...
}

doing so hampers the caller's ability to understand and handle the exceptions that occur. Further, if a later revision of doExchange() introduces a new type of exception that should be treated differently than previous exceptions, there is no easy way to enforce this requirement.

Example Two

Early versions of C++ (C++98, C++03, C++11) included a feature known as Dynamic Exception Specification. This allowed functions to declare what type of exceptions it may throw. It is possible to declare a general class of exception to cover any derived exceptions that may be throw.

int myfunction() throw(std::exception) {
  if (0) throw out_of_range();
  throw length_error();
}

In the example above, the code declares that myfunction() can throw an exception of type "std::exception" thus hiding details about the possible derived exceptions that could potentially be thrown.

See Also