private static int driver()
// This is the driver of the FA.
// If a valid token is found, assigns it to "t" and returns 1.
// If an invalid token is found, assigns it to "t" and returns 0.
// If end-of-stream is reached without finding any non-whitespace character, returns -1.
{
State nextSt; // the next state of the FA
t = "";
state = State.Start;
if (Character.isWhitespace((char) a)) a = getChar(); // get the next non-whitespace character
if (a == -1) // end-of-stream is reached
return -1;
while (a != -1) // do the body if "a" is not end-of-stream
{
c = (char) a;
nextSt = nextState[state.ordinal()][a];
if (nextSt == State.UNDEF) // The FA will halt.
{
if (isFinal(state)) return 1; // valid token extracted
else // "c" is an unexpected character
{
t = t + c;
a = getNextChar();
return 0; // invalid token found
}
} else // The FA will go on.
{
state = nextSt;
t = t + c;
a = getNextChar();
}
}
// end-of-stream is reached while a token is being extracted
if (isFinal(state)) return 1; // valid token extracted
else return 0; // invalid token found
} // end driver
