code: private void pop(final int elements) {
          if (outputStackTop >= elements) {
              outputStackTop -= elements;
          } else {
              // if the number of elements to be popped is greater than the number
              // of elements in the output stack, clear it, and pops the remaining
              // elements from the input stack.
              owner.inputStackTop -= elements - outputStackTop;
              outputStackTop = 0;
          }
      }
docs: Pops the given number of types from the output frame stack.
  
  @param elements
  the number of types that must be popped.