FSM.java

import java.util.ArrayList;

public class FSM
{
  public class State
  {
    final boolean acceptor;
    private final int num;
    final int r0; // what to return if given zero
    final int r1; // what to return if given one
    final int n0; // next state if given zero
    final int n1; // next state if given one

    /**
     * Instantiate a state
     * @param num the current state numer
     * @param r0 what to return if given zero
     * @param r1 what to return if given one
     * @param n0 next state if given zero
     * @param n1 next state if given one
     * @param acceptor is this an accepting state?
     */
    State(int num, int r0, int r1, int n0, int n1, boolean acceptor)
    {
      this.num = num;
      this.r0 = r0;
      this.r1 = r1;
      this.n0 = n0;
      this.n1 = n1;
      this.acceptor = acceptor;
    }

    public int getOutput(int b)
    {
      return (b == 1) ? r1 : r0;
    }

    public int getNext(int b)
    {
      return (b == 1) ? n1 : n0;
    }
  }

  public class StateResult
  {
    final int input;
    final int output;
    final int next;
    
    StateResult(int input, int output, int next)
    {
      this.input = input;
      this.output = output;
      this.next = next;
    }
  }
  
  private ArrayList<State> states;
  private ArrayList<StateResult> results;

  FSM()
  {
    states = new ArrayList<State>();
    results = new ArrayList<StateResult>();
  }

  /**
   * clear and initialise the FSM so counting can start from 1
   */
  public void clear()
  {
    states.clear();
    states.add(new State(0, 0, 0, 0, 0, false)); // zero null state
    results.clear();
  }

  /**
   * add a state to the FSM
   * @param r0 what to return if given 0 
   * @param r1 what to return if given 1
   * @param n0 next state if given 0
   * @param n1 next state if given 1
   * @param acceptor
   */
  public void addState(int r0, int r1, int n0, int n1, boolean acceptor)
  {
    states.add(new State(states.size() + 1, r0, r1, n0, n1, acceptor));
  }

  public static void main(String[] args)
  {
    FSM f = new FSM();
    f.clear();

    f.addState(1,0,3,4,false);
    f.addState(0,1,5,4,false);
    f.addState(1,0,1,6,false);
    f.addState(0,0,4,6,false);
    f.addState(1,0,1,2,false);
    f.addState(1,0,1,3,false);

    f.run("0110111011001");
    
    System.out.printf("  IN|");
    for(StateResult r : f.results)
      System.out.printf("& %d ",r.input);
    System.out.printf("\\\\\n");
    
    System.out.printf(" OUT|");
    for(StateResult r : f.results)
      System.out.printf("& %d ",r.output);
    System.out.printf("\\\\\n");
    
    System.out.printf("NEXT|");
    for(StateResult r : f.results)
      System.out.printf("& %d ",r.next);
    System.out.printf("\\\\\n");
  }

  public void run(String inputs)
  {
    State active = states.get(1); // always start at state 1
                                  // (because MQ dept of mathematics aren't real
                                  // computer scientists)
    for (char c : inputs.toCharArray())
    {
      int i = (c == '1') ? 1 : 0;
      results.add(new StateResult(i, active.getOutput(i), active.getNext(i)));
      //System.out.printf("%d", active.getOutput(i));
      //active = states.get(active.getNext(i));
    }
  }
}