code: public void clear( ) {
  		checkNotClosed( );
  		if ( objects_to_close == null ) {
  			return;
  		}
  		RuntimeException re = null;
  		for ( AutoCloseable ac : objects_to_close ) {
  			try {
  				ac.close( );
  			}
  			catch ( Exception e ) {
  				if ( re == null ) {
  					re = new RuntimeException( e );
  				}
  				else {
  					re.addSuppressed( e );
  				}
  			}
  		}
  		objects_to_close.clear( );
  		if ( re != null ) {
  			throw re;
  		}
  	}
docs: <p>
  {@code clear} closes all resources still present in this {@code Rook} and
  removes them from this {@code Rook}.
  </p>
  
  @throws IllegalStateException
  When this {@code BasicRook} is closed.
  @throws RuntimeException
  When one or more invocations of
  {@link java.lang.AutoCloseable#close() close()} on the collected
  resources throw exception.
  @since 1.0