f.set("foo");
    f.addListener(() -> sneakyThrow(new SomeCheckedException()), directExecutor());
  }

  private static final class SomeCheckedException extends Exception {}

  /** Throws an undeclared checked exception. */
  private static void sneakyThrow(Throwable t) {
    class SneakyThrower<T extends Throwable> {
      @SuppressWarnings("unchecked") // intentionally unsafe for test

    }
    return (short) hextet;
  }

  /**
   * Convert a byte array into an InetAddress.
   *
   * <p>{@link InetAddress#getByAddress} is documented as throwing a checked exception "if IP
   * address is of illegal length." We replace it with an unchecked exception, for use by callers
   * who already know that addr is an array of length 4 or 16.
   *

focus~.custom-control-label::before,.was-validated .custom-control-input:valid:focus~.custom-control-label::before{box-shadow:0 0 0 .2rem rgba(40,167,69,.25)}.custom-control-input.is-valid:focus:not(:checked)~.custom-control-label::before,.was-validated .custom-control-input:valid:focus:not(:checked)~.custom-control-label::before{border-color:#28a745}.custom-file-input.is-valid~.custom-file-label,.was-validated .custom-file-input:valid~.custom-file-label{border-color:#28a745}.custom-file-input.i...

                  (SecureDirectoryStream<Path>) parent,
                  /*
                   * requireNonNull is safe because paths have file names when they have parents,
                   * and we checked for a parent at the beginning of the method.
                   */
                  requireNonNull(path.getFileName()));
        }
      }

      if (!sdsSupported) {

                  (SecureDirectoryStream<Path>) parent,
                  /*
                   * requireNonNull is safe because paths have file names when they have parents,
                   * and we checked for a parent at the beginning of the method.
                   */
                  requireNonNull(path.getFileName()));
        }
      }

      if (!sdsSupported) {

focus~.custom-control-label::before,.was-validated .custom-control-input:valid:focus~.custom-control-label::before{box-shadow:0 0 0 .2rem rgba(40,167,69,.25)}.custom-control-input.is-valid:focus:not(:checked)~.custom-control-label::before,.was-validated .custom-control-input:valid:focus:not(:checked)~.custom-control-label::before{border-color:#28a745}.custom-file-input.is-valid~.custom-file-label,.was-validated .custom-file-input:valid~.custom-file-label{border-color:#28a745}.custom-file-input.i...

	g()
}
</pre>

<p>
it can happen that <code>g</code> prints <code>2</code> and then <code>0</code>.
</p>

<p>
This fact invalidates a few common idioms.
</p>

<p>
Double-checked locking is an attempt to avoid the overhead of synchronization.
For example, the <code>twoprint</code> program might be
incorrectly written as:
</p>

<pre>
var a string
var done bool

func setup() {

="done",Et={onCheck:function(e){return e},onUnCheck:function(e){return e}},Lt=function(){function e(e,t){this._config=t,this._element=e,this._init()}var t=e.prototype;return t.toggle=function(e){e.parents("li").toggleClass(Ft),n.default(e).prop("checked")?this.check(e):this.unCheck(n.default(e))},t.check=function(e){this._config.onCheck.call(e)},t.unCheck=function(e){this._config.onUnCheck.call(e)},t._init=function(){var e=this,t=this._element;t.find("input:checkbox:checked").parents("li").toggl...

     *          since casting to long is monotonic
     * k <= (long) Math.sqrt(x) <= k + 1
     *          since (long) Math.sqrt(k * k) == k, as checked exhaustively in
     *          {@link LongMathTest#testSqrtOfPerfectSquareAsDoubleIsPerfect}
     */
    long guess = (long) Math.sqrt((double) x);
    // Note: guess is always <= FLOOR_SQRT_MAX_LONG.

     *          since casting to long is monotonic
     * k <= (long) Math.sqrt(x) <= k + 1
     *          since (long) Math.sqrt(k * k) == k, as checked exhaustively in
     *          {@link LongMathTest#testSqrtOfPerfectSquareAsDoubleIsPerfect}
     */
    long guess = (long) Math.sqrt((double) x);
    // Note: guess is always <= FLOOR_SQRT_MAX_LONG.