/** 
* This class is used for unsigned binary numbers of 8 bits length 
* 
* @author Mr J
* @version 20040221
*/ 
class BinaryTextField extends java.awt.TextField 
{ 
  // Constructors (as for TextField) 
  public BinaryTextField() 
  { 
    super(); 
  }
  public BinaryTextField(int columns) 
  { 
    super(columns); 
  } 
  public BinaryTextField(String text) 
  { 
    super(text); 
  } 
  public BinaryTextField(String text, int columns) 
  { 
    super(text, columns); 
  } 
  /** 
  * This method returns a valid binary String of 8 bits or passes up an exception 
  * @return java.lang.String
  * @throws BinaryTextFieldException
  */ 
  public String binaryValue() throws BinaryTextFieldException 
  { 
    // Use the TextField built-in method for getting the text
    String s = super.getText();
    if ( isBinary() ) // method to test if is valid binary string 
    { 
      return s; 
    } 
    else 
    { 
      return null; // return a null value on error 
    }
  }

  /**
  * This method tests the binary number to see if it is a valid 
  * 8-bit binary unsigned integer 
  * @return true if the byte is valid
  * @throws BinaryTextFieldException
  */
  public boolean isBinary() throws BinaryTextFieldException 
  { 
    boolean ok = true; 
    String s = super.getText(); 
    if ( s.length() != 8 ) // byte must have 8 bits 
    { 
      // throw an exception with a custom error message 
      ok = false; 
      throw new BinaryTextFieldException("Bad byte length"); 
    } 
    else 
    { 
      int pos = 0; 
      char c; 
      while ( (pos < 8) && (ok) ) 
      { 
        c = s.charAt(pos); 
        if ( (c != '0') && (c != '1') ) // each bit must be a 1 or a 0 
        { 
          ok = false; 
          throw new BinaryTextFieldException("Bad digit " + c + " at " + (++pos)); 
        } 
        pos++; 
      } 
      return (ok); 
    } 
  }
  /** 
  * This method converts a valid, unsigned binary String of 8 bits to an integer 
  * @return int
  * @throws BinaryTextFieldException if value in field is invalid
  */ 
  public int convert() throws BinaryTextFieldException
  { 
	int sum = 0;
	int weight = 1;
	String s = binaryValue();
    // start at the LSB (right end of String)
    // if the digit is a 1, add it in
	for (int pos = 7; pos >= 0; pos--)
	{
		if ( s.charAt(pos) == '1' )
		{
			sum += weight;
		}
		weight *= 2; // next digit up is worth twice as much as this one
	}
	return(sum);
  }
}