boolean haveBeenCalled;

          @Override
          public Integer computeNext() {
            if (haveBeenCalled) {
              throw new AssertionError("Should not have been called again");
            } else {
              haveBeenCalled = true;
              sneakyThrow(new SomeCheckedException());
              throw new AssertionError(); // unreachable
            }
          }

          boolean haveBeenCalled;

          @Override
          public Integer computeNext() {
            if (haveBeenCalled) {
              throw new AssertionError("Should not have been called again");
            } else {
              haveBeenCalled = true;
              sneakyThrow(new SomeCheckedException());
              throw new AssertionError(); // unreachable
            }
          }