code: public String getValuesAsString() {
  		StringBuilder builder = new StringBuilder();
  		for(E row: rowKeys.keySet())
  			for(E col: colKeys.keySet()) {
  				builder.append(getValueAsString(row, col, true));
  				builder.append('\n');
  			}
  		return builder.toString();
  	}
docs: Returns a String representation of all matrix entries.
  @return String representation of all matrix entries
  @see #getValueAsString(Object, Object, boolean)