import java.util.*;

abstract class Worker {
  public Worker() {
    hunger = 0;
    allWorkers.addElement(this);
  }
  public void work () {
    hunger++;
    workDone++;
    System.out.println("whistle");
  }

  public void eat () {
    hunger--;
    System.out.println("yum");
  }

  public void live() {
    work();
    eat();
  }

  abstract public void printWorksWith(); // Prints the names of people one 
                                    // works with; depends on kind of worker.
  
  public String toString() {
    return "hunger level is: " + hunger;
  }

  public static void showWorkForce() {
    int i = 0;
    System.out.println("All the workers in the world:");
    for (i = 0; i < allWorkers.size(); i++) {
      System.out.println("    " + allWorkers.elementAt(i));
    }
  }

  protected int hunger;
  private static int workDone = 0;
  private static Vector allWorkers = new Vector();
}

class TA extends Worker {  
  public TA(String p) {
    super();
    prof = p;
    classList = new Vector();
  }

  public void workAlternate() {  // used in lecture 11 as the "work" method
    super.work();      /* do whatever a Worker does to work */
    System.out.println("let me help");
  }

  public void work() {
    hunger++;
    System.out.println("let me help");
  }

  public void printWorksWith() {
      System.out.println("Professor of course: " + prof);
      System.out.println("Students in section: " + classList);
  }  

  public String toString() {
    return super.toString() + ", class size: " + classList.size();
  }

  public void add(String student) {
    classList.addElement(student);
  }

   private String prof;
   private Vector classList;
}

class Lecture12 {
  static void foo (Worker w) {
    System.out.println("A week in a worker's life.");
    for (int i = 0; i < 5; i++) {
      w.live();
    }
    w.eat();
    w.eat();
    // t.add("Jeff");  not
  }

  static void bar (TA t) {
    t.live();
    t.add("Jeff");
  }
    
  public static void main(String[] argv) {
    /* If Worker is not abstract, the following works. 
    System.out.println("\nWorker w1 lives.");
    Worker w1 = new Worker();
    w1.live();
    foo(w1);
    // bar(w1); not legal, even if Worker is not abstract
    */
      
    System.out.println("\nTA t1 lives.");
    TA t1 = new TA("Yelick");
    t1.live();
    foo(t1);
    bar(t1);
    t1.printWorksWith();

    Worker.showWorkForce();
    System.out.println("\n");

    // test interfaces (below)
    IntBox ib1 = new IntBox(2);
    IntBox ib2 = new IntBox(3);
    System.out.println("ib1.lessThan(ib2) is: " + ib1.lessThan(ib2));
    ib2.negate();
    System.out.println("...after negating ib2");
    System.out.println("ib1.lessThan(ib2) is: " + ib1.lessThan(ib2));
  }
}


/* * * * * * * * * * * * Interfaces * * * * * * * * * * * * * * */

interface Negatable {
   void negate();
}
    
interface Comparable {
   boolean lessThan (Comparable c);
   boolean greaterThan (Comparable c);
}
    
class IntBox implements Negatable, Comparable {
  public IntBox(int v) { value = v; }
  public int getValue() { return value; }
  public void setValue(int v) { value = v; }

  public void negate() { value = -value; }
  public boolean lessThan (Comparable c) { return value < ((IntBox) c).value; }
  public boolean greaterThan (Comparable c) { return value > ((IntBox) c).value; }

  private int value;

}