ERR04-J. Do not exit abruptly from a finally block

Never 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 completion. Statements that cause the finally block to terminate abruptly also cause the try block to terminate abruptly and consequently mask any exception thrown from the try or catch blocks [JLS 2005].

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("logic done");
      return true;
    }
  }
}

The IllegalStateException is suppressed by the abrupt termination 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("logic done");
    }
    // Any return statements must go here; applicable only when exception is thrown conditionally
  }
}

ERRO4-EX0: Control flow statements whose destination is within the finally block are perfectly acceptable.

For instance, the following code does not violate this rule, because the break statement exits the while loop, but not 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

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

Related Guidelines

Bibliography

      06. Exceptional Behavior (ERR)