ERR07-J. Do not throw RuntimeException, Exception, or Throwable

Methods must not throw RuntimeException, Exception, or Throwable. Handling these exceptions requires catching RuntimeException, which is disallowed by rule ERR08-J. Do not catch NullPointerException or any of its ancestors. Moreover, throwing a RuntimeException can lead to subtle errors; for example, a caller cannot examine the exception to determine why it was thrown and consequently cannot attempt recovery.

Methods can throw a specific exception subclassed from Exception or RuntimeException. Note that it is permissible to construct an exception class specifically for a single throw statement.

Noncompliant Code Example

The isCapitalized() method in this noncompliant code example accepts a string and returns true when the string consists of a capital letter followed by lowercase letters. The method also throws a RuntimeException when passed a null string argument.

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()));
}

A calling method must also violate rule ERR08-J. Do not catch NullPointerException or any of its ancestors to determine whether the RuntimeException was thrown.

Compliant Solution

This compliant solution throws NullPointerException to denote the specific exceptional condition.

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()));
}

Note that the null check is redundant; if it were removed, the subsequent call to s.equals("") would throw a NullPointerException when s is null. However, the null check is suggested because it explicitly indicates the programmer's intent. More complex code may require explicit testing of invariants and appropriate throw statements.

Noncompliant Code Example

This noncompliant code example specifies the Exception class in the throws clause of the method declaration for the doSomething() method.

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

Compliant Solution

This compliant solution declares a specific exception in the throws clause of the method declaration for the doSomething() method.

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

Exceptions

ERR07-EX0: Classes that sanitize exceptions to comply with a security policy are permitted to translate specific exceptions into more general exceptions. This translation could potentially result in throwing RuntimeException, Exception, or Throwable in some cases, depending on the details of the security policy.

Risk Assessment

Throwing RuntimeException, Exception, or Throwable prevents classes from catching the intended exceptions without catching other unintended exceptions as well.

Related Guidelines

Bibliography

      06. Exceptional Behavior (ERR)