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Wiki MarkupNever use {{return}}, {{break}}, {{continue}}, or {{throw}} statements within a {{finally}} block. When program execution enters a {{try}} block that has a {{finally}} block, the {{finally}} block always executes , regardless of whether the {{try}} block (or any associated {{catch}} blocks) executes to normal completion. Statements that cause the {{finally}} block to terminate complete abruptly also cause the {{try}} block to terminate complete abruptly and consequently mask suppress any exception thrown from the {{try}} or {{catch}} blocks \[[JLS 2005|http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.20.2]\]. According to The Java Language Specification, §14.20.2, "Execution of try-finally and try-catch-finally" [JLS 2015]:

If execution of the try block completes abruptly for any other reason R, then the finally block is executed. Then there is a choice:

• If the finally block completes normally, then the try statement completes abruptly for reason R.
• If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).

Noncompliant Code Example

In this noncompliant code example, the finally block completes abruptly because of a return statement in the block.:

class TryFinally {
  private static boolean doLogic() {
    try {
      throw new IllegalStateException();
    } finally {
      System.out.println("Uncaughtlogic Exceptiondone");
      return true;
    }
  }

  public static void main(String[] args) {
    doLogic();
  }
}

The IllegalStateException is suppressed by the abrupt termination completion of the finally block caused by the return statement.

Compliant Solution

This compliant solution removes the return statement from the finally block.:

class TryFinally {
  private static boolean doLogic() {
    try {
      throw new IllegalStateException();
    } finally {
      System.out.println("Caughtlogic Exceptiondone");
    }
    // Any return statements must go here; 
    // applicable only when exception is thrown conditionally
  }
}
  public static void main(String[] args) {
    doLogic();
  }
}

Risk Assessment

Exceptions

ERRO4-J-EX0: Control flow statements whose destination is within the finally block are perfectly acceptable. For example, the following code does not violate this rule because the break statement exits within the while loop but not within the finally block:

class TryFinally {
  private static boolean doLogic() {
    try {
      throw new IllegalStateException();
    } finally {
      int c;
      try {
        while ((c = input.read()) != -1) {
          if (c > 128) {
            break;
          }
        }
      } catch (IOException x) {
        // Forward to handler
      }
      System.out.println("logic done");
    }
    // Any return statements must go here; applicable only when exception is thrown conditionally
  }
}

Risk Assessment

Abrupt completion of Exiting abruptly from a finally block masks any exceptions thrown inside the associated try and catch blocks.

Related Vulnerabilities

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

Bibliography

\[[Bloch 2005|AA. Bibliography#Bloch 05]\] Puzzle 36: Indecision
\[[Chess 2007|AA. Bibliography#Chess 07]\] 8.2 Managing Exceptions, "The Vanishing Exception"
\[[JLS 2005|AA. Bibliography#JLS 05]\] [§14.20.2, Execution of try-catch-finally|http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.20.2]
\[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE-705|http://cwe.mitre.org/data/definitions/705.html] "Incorrect Control Flow Scoping" and [CWE-584|http://cwe.mitre.org/data/definitions/584.html] "Return Inside Finally Block"

Automated Detection

Related Guidelines

Bibliography

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