TuringMachine.java

Below is the syntax highlighted version of TuringMachine.java from §7.4 Kleene Theorem.

/*************************************************************************
 *  Compilation:  javac TuringMachine.java
 *  Execution:    java TuringMachine
 *  Dependencies: Stack.java Control.java Tape.java Transition.java
 *  
 *  % java TuringMachine comparator.tur "1101<1110"
 *
 *  Reads in a .tur file describing a Turing machine, and simulates
 *  the input on the machine.
 *
 *************************************************************************/


public class TuringMachine {
    private Control control;          // control unit
    private Tape tape;                // ticker tape

    // input file
    public TuringMachine(In in) {
        control = new Control();
        String s = "";

        // the vertices / states
        while (!s.equalsIgnoreCase("vertices")) {
            s= in.readLine().trim();
        }
        while (!s.equalsIgnoreCase("edges")) {
            s = in.readLine().trim();
            if (s.equals("")) continue;
            if (s.startsWith("//")) continue;
            if (s.equalsIgnoreCase("edges")) continue;
            String[] fields = s.split("\\s");
            control.addState(fields[0], fields[1]);
        }

        // the edges / transitions
        while (!s.equalsIgnoreCase("tapes")) {
            s = in.readLine().trim();
            if (s.equals("")) continue;
            if (s.startsWith("//")) continue;
            if (s.equalsIgnoreCase("tapes")) continue;
            String[] fields = s.split("\\s");
            control.addTransition(fields[0], fields[1], fields[2], fields[3]);
        }
    }

    // simulate the Turing machine
    public void simulate(String input) {
        tape = new Tape(input);                                       // starting tape
        State state = control.getState();                             // starting state

        // do fetch, decode, execute cycle
        while(!state.isHalt() && !state.isYes() && !state.isNo()) {
            //// System.out.println(state);
            String read = tape.read();                                // current character
            Transition transition = control.getTransition(read);      // transition to follow
            if (transition != null) {                                 // state in same state if no transition
               state = transition.getNextState();                     // next state
               control.setState(state);                               // update the state
               tape.write(transition.getWrite());                     // write the symbol
            }
            if      (state.isLeft())  tape.left();                    // move tape left
            else if (state.isRight()) tape.right();                   // or move tape right
        }

        if      (state.isYes())  System.out.println("Accepted");
        else if (state.isNo())   System.out.println("Rejected");
        else if (state.isHalt()) System.out.println("Halted");
    }

    public static void main(String[] args) {
        In in = new In(args[0]);
        TuringMachine tm = new TuringMachine(in);
        tm.simulate(args[1]);
    }
	
}