Connector.java

public class Connector {

	// Implement an immutable connector that connects two points on the game board.
	// Invariant: 1 <= myPoint1 < myPoint2 <= 6.

	private int myPoint1, myPoint2;

	public Connector (int p1, int p2) {
		if (p1 < p2) {
			myPoint1 = p1;
			myPoint2 = p2;
		} else {
			myPoint1 = p2;
			myPoint2 = p1;
		}
	}

	public int endPt1 ( ) {
		return myPoint1;
	}

	public int endPt2 ( ) {
		return myPoint2;
	}

	public boolean equals (Object obj) {
		Connector e = (Connector) obj;
		return (e.myPoint1 == myPoint1 && e.myPoint2 == myPoint2);
	}

	public String toString ( ) {
		return "" + myPoint1 + myPoint2;
	}
	
	public boolean isOK()
	{
		if (myPoint1 == myPoint2)
			return false;
		
		if (myPoint1 < 1 || myPoint1 > 6 || myPoint2 < 1 || myPoint2 > 6)
			return false;
		
		return true;
	}

	public int hashCode()
	{
		return myPoint1 ^ myPoint2;
	}
	
	// Format of a connector is endPoint1 + endPoint2 (+ means string concatenation),
	// possibly surrounded by white space. Each endpoint is a digit between
	// 1 and 6, inclusive; moreover, the endpoints aren't identical.
	// If the contents of the given string is correctly formatted,
	// return the corresponding connector.  Otherwise, throw IllegalFormatException.

	public static Connector toConnector (String s) throws IllegalFormatException
	{
		if (s == null) 
			throw new IllegalFormatException("Null string");
		else if (s.length() <= 1) 
			throw new IllegalFormatException("String with length <= 1");

		int p1, p2;
		p1 = p2 = 0;

		boolean found_number = false;
		int i, numcount;
		i = numcount = 0;

		while (i < s.length())
		{
			if(Character.isWhitespace(s.charAt(i)))
			{
				if(found_number) 
				{
					throw new IllegalFormatException("Whitespace between endpoints");
				}
			}
			else
			{
				if(s.charAt(i) < '1' || s.charAt(i) > '6') 
					throw new IllegalFormatException("Not an endpoint");
				else
				{
					++numcount;
					if(numcount == 1)
					{ 
						p1 = s.charAt(i) - '0'; 
						found_number = true;
					}
					else if(numcount == 2) 
					{
						p2 = s.charAt(i) - '0';
						found_number = false;
					}
					else 
						throw new IllegalFormatException("More than 2 endpoints found"); //more than 2 endpoints
				}
			}
			++i;
		}


		if(p1 != p2) 
			return new Connector(p1,p2);
		else 
			throw new IllegalFormatException("Endpoints are the same");
	}
}