EXC33-J. Do not throw RuntimeException or Exception

A method should never throw RuntimeException or Exception. This is because handling these requires catching RuntimeException, which is forbidden in [EXC32-J. Do not catch RuntimeException]. Moreover, throwing a RuntimeException can lead to subtle errors such as a caller who fails to retrieve a return value from the offending method, is unable to check for appropriate feedback. The Java Language Specification (Section 8.4.7 Method Body) allows the declaration of a method with a return type without making it necessary to return a value if a runtime exception is thrown from within the method [[JLS 05]].

Instead, always throw an exception subclassed from Exception. It is permissible to construct an exception class specifically for a single throw statement.

Noncompliant Code Example

The following function takes a string and returns true if it consists of a capital letter succeeded by lowercase letters. To handle corner cases, it checks for them and throws exceptions if they would prevent normal analysis.

boolean isCapitalized(String s) {
  if (s == null) {
    throw new RuntimeException("Null String");
  }
  if (s.equals("")) {
    return true;
  }
  String first = s.substring( 0, 1);
  String rest = s.substring( 1);
  return (first.equals( first.toUpperCase()) &&
          rest.equals( rest.toLowerCase()));
}

In order to handle the case of passing in a null string, code calling this function would have to catch RuntimeException, which violates EXC32-J. Do not catch RuntimeException

Compliant Solution

An exception specifically devoted to the error would be more appropriate.

boolean isCapitalized(String s) {
  if (s == null) {
    throw new NullPointerException();
  }
  if (s.equals("")) {
    return true;
  }
  String first = s.substring( 0, 1);
  String rest = s.substring( 1);
  return (first.equals( first.toUpperCase()) &&
          rest.equals( rest.toLowerCase()));
}

Noncompliant Code Example

This noncompliant code snippet uses a broad Exception class in the throws statement within the method declaration.

private void doSomething() throws Exception {
//...
}

Compliant Solution

To be compliant, be as specific as possible while declaring exceptions and heed the given abstraction level.

private void doSomething() throws IOException {
//...
}

Risk Assessment

Throwing RuntimeException, Exception, or General prevents classes from catching your exception without catching other unintended exceptions as well.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[MITRE 09]] CWE ID 397 "Declaration of Throws for Generic Exception", CWE ID 537 "Information Leak Through Java Runtime Error Message"
[[Goetz 04b]]
[[Tutorials 08]] Unchecked Exceptions — The Controversy

EXC03-J. Try to recover gracefully from system errors      11. Exceptional Behavior (EXC)      EXC30-J. Do not exit abruptly from a finally block