Threads

[Duran Harris]

Hi...so I'm busy messing around with threads and I decided to make a small game.It's not working well so far though.My cat thread isn't running.Also I'm not sure that I've used wait() and notify() correctly.

The idea is that I create a Mouse and cat class.Then I create a single Cat and multiple Mouse threads.When a mouse is created it gets put in a static hash map.I use math.random() in the Cat thread to create a random chance of the cat catching(and killing) a mouse.Not quite sure how I should go about this..Oh yes..also the idea is that there should only be one mouse running around at a time.The game is meant to end either when cheese=0 OR when the mice have all been killed...
I just can't seem to get the Cat thread to output anything....any suggestions??

import java.lang.Math.*;
import java.util.*;
class Cat extends Thread
{
 
public Cat()
{
 
Mouse.theGuard=this;
 
}
 
public void run()
{ 
 
while(Mouse.preyArray.size()>0)
{
synchronized(Mouse.theGuard)
   {
    int  aKill= (int)Math.random()*3;
    
        if(aKill<=3&Mouse.preyArray.get(aKill)!=null)
  {System.out.print("Cat killed "+Mouse.preyArray.get(aKill));
  Mouse.preyArray.remove(aKill);   
          notifyAll();
  }
   }
}
 
}
public static void main(String[] args)
{   
     Cat aCat = new Cat();
     new Mouse("Jerry").start();
     new Mouse("Chuck").start();
     new Mouse("Giggles").start();
     aCat.start();
}
 
}
class Mouse extends Thread
{
 
static Map<Mouse,String> preyArray= new HashMap<Mouse,String>();
static Cat theGuard;
static int cheese =500;
String name;
 
public Mouse(String name)
{
preyArray.put(this,name);
this.name=name;


}
  public String toString()
  {
  String mouseString ="";
  mouseString+=this.name;
  return mouseString;
  
  }
 
public void run()
{ 
    {while(cheese>0)
synchronized(theGuard)
    
{
         
System.out.print(this.name+" ate some cheese while cat was asleep!");
cheese--;
        
  try{theGuard.wait(); 
      }
      catch(InterruptedException IE)
  {
  } 
}
 
    }
}
 
}

[ December 29, 2008: Message edited by: Duran Harris ]

[Anthony Accioly]

Hey,

Your program had several issues...
1) The program was freezing because everyone was waiting at the cat monitor
2) You forgot to interrupt the mouse thread once you killed it
3) The static HashMap approach wasen't really working

Here is a version of the program that seens to be working allright for me:

import java.lang.Math.*;
import java.util.*;
 
class Cat extends Thread {
 
    public Cat() {
        Mouse.theGuard = this;
    }
 
    public void run() {
        // prevents cat from running after cheese is zero
        while (Mouse.preyArray.size() > 0 && Mouse.cheese > 0) {
            synchronized (Mouse.theGuard) {
                int aKill = (int) Math.random() * 3;
 
                if (aKill <= 3 & Mouse.preyArray.get(aKill) != null) {
                    String killedMouseName = Mouse.preyArray.get(aKill).name;
 
                    if (Mouse.cheese > 0) {
                        System.out.println("Cat killed " + killedMouseName);
 
                        // interrupt mouse thread and remove the mouse of the list
                        Mouse m = Mouse.preyArray.get(aKill);
                        m.interrupt();
                        Mouse.preyArray.remove(aKill);
 
                        notifyAll();
                        yield();
                    }
                }
            }
        }
    }
 
    public static void main(String[] args) {
        Cat aCat = new Cat();
        Mouse m1 = new Mouse("Jerry");
        Mouse m2 = new Mouse("Chuck");
        Mouse m3 = new Mouse("Giggles");
 
        m1.start();
        m2.start();
        m3.start();
        aCat.start();
 
        // waits for every thread to finish
        try {
            aCat.join();
            m1.join();
            m2.join();
            m3.join();
        } catch (InterruptedException ex) {
        }
 
        System.out.println("\n\nCheese Left: " + Mouse.cheese);
        System.out.println("----------");
        if (Mouse.cheese > 0) {
            System.out.println("CAT Wins!");
        } else {
            System.out.println("MOUSES wins!");
        }
    }
}
 
class Mouse extends Thread {
 
    static List<Mouse> preyArray = new ArrayList<Mouse>();
    static Cat theGuard;
    static int cheese = 100;
    String name;
 
    public Mouse(String name) {
        this.name = name;
        preyArray.add(this);
    }
 
    public String toString() {
        String mouseString = "";
        mouseString += this.name;
        return mouseString;
    }
 
    public void run() {
        {
 
            while (cheese > 0) {
                synchronized (theGuard) {
                    // so we know if the thread has been interrupted
                    if (isInterrupted()) {
                        return;
                    }
                    if (cheese > 0) {
                        cheese--;
                        System.out.println(this.name + " ate some cheese while cat was asleep!");
                    }
                    // notify other objects and release the lock
                    theGuard.notifyAll();
                    yield();
                }
            }
        }
    }
}

ps: There is a game development forum here at the saloon .

Cheers

[ December 29, 2008: Message edited by: Anthony Accioly ]
[ December 29, 2008: Message edited by: Anthony Accioly ]