code: public void setPermissionsFromMaskString(String mask) {
  		if (mask.length() != 4) {
  			throw new IllegalArgumentException("Mask length must be 4");
  		}
  
  		try {
  			setPermissions(new UnsignedInteger32(String.valueOf(Integer
  					.parseInt(mask, 8))));
  		} catch (NumberFormatException nfe) {
  			throw new IllegalArgumentException(
  					"Mask must be 4 digit octal number.");
  		}
  	}
docs: Set permissions given a UNIX style mask, for example '0644'
  
  @param mask
  mask
  
  @throws IllegalArgumentException
  if badly formatted string