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Thread: TimeUnit.SECONDS.sleep(x) stops simulation

  1. #1
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    Default TimeUnit.SECONDS.sleep(x) stops simulation

    Hey guys! I get a NullPointerException Error and really dont know what to do anymore ... Ive tried anything I know and nothing helped so I hope someone here can help me!

    I simulate bacteria and penezilin(shroom) in a petri dish. So heres the code

    bacteria:

    import java.util.ArrayList;
     
    public class Bakterium extends Lebewesen
    {
        //Vermehrungsrate 0.25; Sterberate 0.0
        public Bakterium(int position, int alter, ArrayList<Lebewesen> lebewesen)
        {
            super(position, alter, lebewesen, 0.25, 0.0);
        }
     
        public void vermehren()
        {
            Bakterium b;
            int wo;
            wo=super.platzSuchen();
            if (wo>0) {
                b = new Bakterium(wo, 0, super.lebewesenGeben());
     
                super.lebewesenGeben().add(b);
            }
     
            }
     
        public boolean istPilz()
        {
            return false;
        }
        }

    JFrame:

    import java.util.ArrayList;
    import javax.swing.*;
    import java.awt.*;
     
    public class Darstellung extends JFrame
    {
        ArrayList<Lebewesen> lebewesen;
     
        public Darstellung(ArrayList<Lebewesen> nLebenwesen)
        {
            super("Population"); //Name des Fensters/JFrames
            setSize(550,580);
            setVisible(true);
            lebewesen=nLebenwesen;
        }
     
           public void paint(Graphics g)
        {
            g.setColor(Color.yellow);
            g.fillRect(0, 0, 550, 580);
     
            g.setColor(Color.white);
            g.fillRect(25, 50, 500, 500);      
     
            Lebewesen l;
     
            for (int i=0; i<lebewesen.size(); i++)
            {
                l = lebewesen.get(i);
                if (l.istPilz()==false)
                {
                    g.setColor(Color.red);    
                }
                else
                {
                    g.setColor(Color.blue);
                }
     
                int x=(l.positionGeben()%100);
                if (x==0) {x=100;}
                int y=(l.positionGeben()-x);
                x=x*5+20;
                y=y/100*5+50;
                g.fillOval(x, y, 5, 5);
            }
        }
    }

    shroom:

    {
        public Pilz(int position, int alter, ArrayList<Lebewesen> lebewesen)
        {
            super(position, alter, lebewesen, 0.9, 0.2);
        }
     
        public void vermehren()
        {
            Pilz p;
            int wo;
            wo=super.platzSuchen();
            if (wo>0) {
                p=new Pilz(wo, 0, super.lebewesenGeben());
                super.lebewesenGeben().add(p);
            }
        }
     
        public boolean istPilz()
        {
            return true;
        }
     
        public boolean istNachbar(int pos)
        {
            int position=super.positionGeben();
            if ((position==(pos+1))||
                (position==(pos-1))||
                (position==(pos+99))||
                (position==(pos+100))||
                (position==(pos+101))||
                (position==(pos-99))||
                (position==(pos-100))||
                (position==(pos-101)))
                return true; else return false;
        }
     
        public void bakterienAbtoeten()
        {
            Lebewesen l=null;
            ArrayList<Lebewesen> lebewesen;
            lebewesen=super.lebewesenGeben(); 
            for (int i=0; i<lebewesen.size(); i=i++)
            {       
                    l=lebewesen.get(i);
                    if((istNachbar(l.positionGeben())==true)&& (l.istPilz()==false))
                    {lebewesen.remove(i);}
            } 
            lebewesen.trimToSize();        
        }   
        }

    Simlation:

    import java.util.ArrayList;
    import java.util.Random;
    import java.awt.*;
    import javax.swing.*;
     
    public class Simulation
    {
        private ArrayList<Lebewesen> lebewesen;
        private Random rand;
     
        public Simulation()
        {
            rand=new Random();
            lebewesen=new ArrayList<Lebewesen>();
        }
     
        public void lebewesenErzeugen(int anzBakterien, int anzPilze)
        {
            //random bakterium
            for (int i=0; i<anzBakterien; i=i+1)
            {
                Bakterium b;
                b=new Bakterium(rand.nextInt(10000)+1, rand.nextInt(5), lebewesen);
                lebewesen.add(b);
     
            }
            //random pilz
            for(int i=0; i<anzPilze; i=i+1)
            {
                Pilz p;
                p=new Pilz(rand.nextInt(10000)+1, 0, lebewesen);
                lebewesen.add(p);
            }
     
        }
     
        public void simulationStarten(int dauer)
        {
            Darstellung d=new Darstellung(lebewesen);
            lebewesenErzeugen(1,1);
            for (int i=0; i<dauer; i=i+1)
            {  
                pilzeToetenBakterienAb();
                alleLebewesenVermehrenSich();
                alleLebewesenAltern();
                lebewesen.trimToSize();
            }
        }
     
        private void alleLebewesenAltern()
        {
            Lebewesen l;
            double wahrscheinlichkeit;
            for (int i=0; i<lebewesen.size(); i++)
            {
                l=lebewesen.get(i);
                l.altern();
                wahrscheinlichkeit=rand.nextDouble();
                if ((wahrscheinlichkeit<l.pSterbenGeben()))
                {
                    lebewesen.remove(i);
                }
            }
        }
     
        private void pilzeToetenBakterienAb()
        {
            Lebewesen l;
            for (int i=0; i<lebewesen.size(); i=i+1)
            {
                l=lebewesen.get(i);
                l.bakterienAbtoeten();
            }
        }
     
        private void alleLebewesenVermehrenSich()
        {
            Lebewesen l;
            double wahrscheinlichkeit;
            int anzahl=lebewesen.size();
            for (int i=0; i<anzahl; i++)
            {
                l=lebewesen.get(i);
                wahrscheinlichkeit=rand.nextDouble();
                if ((wahrscheinlichkeit<l.pVermehrungGeben()))
                {
                    l.vermehren();
                }
            }
        }
     
        public int anzahlLebewesen()
        {
            int l;
            l=lebewesen.size();
            return l;
        }
    }

    lifeform:

    import java.util.ArrayList;
     
    public class Lebewesen{
     
        private int alter;
        private int position;
        private double pVermehrung;
        private double pSterben;
        private ArrayList<Lebewesen> lebewesen;
     
        public Lebewesen(int nPosition, int nAlter, ArrayList<Lebewesen> nLebewesen, 
        double nPVermehrung, double nPSterben)
        {
            position=nPosition;
            alter=nAlter;
            pVermehrung=nPVermehrung;
            pSterben=nPSterben;
        }
     
        public void altern()
        {
            alter=alter++;
            pSterben=pSterben+0.05;
        }
     
        private boolean istFrei(int wo)
        {
            boolean ergebnis;
            ergebnis=true;
            Lebewesen l;
            for (int i=0; i<lebewesen.size(); i++)
            {
                l=lebewesen.get(i);
                if (wo==l.positionGeben()) {ergebnis=false;}
            }
            return ergebnis;
        }
     
        public void vermehren()
        {
            //nur Pilze und Bakterien
        }
     
        public int platzSuchen()
        {
            int ergebnis=-1;
            //links
            if (istFrei(position-1)) ergebnis=position-1; else
            // links oben
            if (istFrei(position-101)) ergebnis=position-101; else 
            // oben
            if (istFrei(position-100)) ergebnis=position-100; else
            // rechts oben
            if (istFrei(position-99)) ergebnis=position-99; else
            // rechts
            if (istFrei(position+1)) ergebnis=position+1; else
            // rechts unten
            if (istFrei(position+101)) ergebnis=position+101; else
            // unten
            if (istFrei(position+100)) ergebnis=position+100; else
            // links unten
            if (istFrei(position+99)) ergebnis=position+99; else
            // nichts frei
            if (ergebnis<1 || ergebnis>10000) ergebnis=-1;
            return ergebnis;
        }
     
        // weitere Methoden
        public int alterGeben() {return alter;}
        public int positionGeben() {return position;}
        public double pSterbenGeben() {return pSterben;}
        public double pVermehrungGeben() {return pVermehrung;}
        public ArrayList<Lebewesen> lebewesenGeben(){return lebewesen;}
     
        //wird benötigt auch wenn später überschrieben
        public boolean istPilz() {return true;}
        public void bakterienAbtoeten() { /**void -> kein return**/}
    }

    Yes I am from Germany.

    So when I create an object of simulation and call the method simulationStarten(int dauer) [dauer means duration] it opens the JFrame with 2 dots, the created shroom and bacteria and then it says:

    java.lang.NullPointerException
    at Pilz.bakterienAbtoeten(Pilz.java:45)
    at Simulation.pilzeToetenBakterienAb(Simulation.java: 72)
    at Simulation.simulationStarten(Simulation.java:43)

    the method with the problem is:

       public void bakterienAbtoeten()
        {
            Lebewesen l;
            ArrayList<Lebewesen> lebewesen;
            lebewesen=super.lebewesenGeben(); 
            [I]for (int i=0; i<lebewesen.size(); i=i++)[/I]
            {       
                    l=lebewesen.get(i);
                    if((istNachbar(l.positionGeben())==true)&& (l.istPilz()==false))
                    {lebewesen.remove(i);}
            } 
            lebewesen.trimToSize();        
        }

    the fat code is marked. And if I delete this method out of simulationStarten(int dauer) the same error occours in:

        private boolean istFrei(int wo)
        {
            boolean ergebnis;
            ergebnis=true;
            Lebewesen l;
            [B]for (int i=0; i<lebewesen.size(); i++)[/B]
            {
                l=lebewesen.get(i);
                if (wo==l.positionGeben()) {ergebnis=false;}
            }
            return ergebnis;
        }

    what is the problem with my "for loop"?

    I hope someone can help me!

    Thanks in advance!


  2. #2
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    Default Re: NullPointerException in a "for loop"

    In the Lebewesen class you have this private member:

    private ArrayList<Lebewesen> lebewesen;

    and this constructor:

    public Lebewesen(int nPosition, int nAlter, ArrayList<Lebewesen> nLebewesen, 
        double nPVermehrung, double nPSterben)

    The private member is never set. You are missing a single line of code:

    lebewesen = nLebwesen;

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    CrusoCraruso (January 20th, 2014)

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    Default Re: NullPointerException in a "for loop"

    This is the kind of thought process you should follow when debugging your code.

    Let's focus on the problem as indicated by the error:
    ArrayList<Lebewesen> lebewesen;
    lebewesen=super.lebewesenGeben(); 
     
    // the error statement, indicating that lebewesen is null
    for (int i=0; i<lebewesen.size(); i=i++)

    I've indicated by the comment above what I think is happening, and the two statements previous suggest:

    1. The ArrayList lebewesen is created locally, not initialized
    2. The statement:

    lebewesen=super.lebewesenGeben();

    does not change #1.

    So, searching for the method , I found this in class Lebewesen:
    public ArrayList<Lebewesen> lebewesenGeben()
    {
        return lebewesen;
    }

    Then, looking for the initialization of lebewesen, something like:

    lebewesen = new ArrayList<Lebewesen>();

    I couldn't find anything similar in class Lebewesen, though I see it in class Simulation. I admit that I get a bit distracted by the German variables, but I don't think that's the problem. Where is lebewesen initialized in class Lebewesen so that lebewesenGeben() returns something other than null?
    Last edited by GregBrannon; January 20th, 2014 at 09:22 AM. Reason: Forgot to add code tags.

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    Default Re: NullPointerException in a "for loop"

    At first glance private ArrayList<Lebewesen> lebewesen of class Lebewesen is not being initialized. That's why you getting NPE.

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    CrusoCraruso (January 20th, 2014)

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    Default Re: NullPointerException in a "for loop"

    I really forgot that single line of code "lebewesen = nLebwesen;" in the constructor of Lebewesen. Cant believe I forgot that.

    Thanks to all of you. That solved it actually!!

    --- Update ---

    Hey guys! I got a new problem ^^

    Why does when I call "warte(int)" the simulation stop?

    import java.util.ArrayList;
    import java.util.Random;
    import java.awt.*;
    import javax.swing.*;
    import java.util.concurrent.TimeUnit;
     
    public class Simulation
    {
        private ArrayList<Lebewesen> lebewesen = new ArrayList<Lebewesen>();
        private Random rand;
     
        public Simulation()
        {
            rand=new Random();
            lebewesen=new ArrayList<Lebewesen>();
        }
     
        public void lebewesenErzeugen(int anzBakterien, int anzPilze)
        {
            //random bakterium
            for (int i=0; i<anzBakterien; i=i+1)
            {
                Bakterium b;
                b=new Bakterium(rand.nextInt(10000)+1, rand.nextInt(5), lebewesen);
                lebewesen.add(b);
     
            }
            //random pilz
            for(int i=0; i<anzPilze; i=i+1)
            {
                Pilz p;
                p=new Pilz(rand.nextInt(10000)+1, 0, lebewesen);
                lebewesen.add(p);
            }
     
        }
     
        public void simulationStarten()
        {
            int dauer=999999999;
            Darstellung d=new Darstellung(lebewesen);
            lebewesenErzeugen(1,1);
            for (int i=0; i<dauer; i++)
            {  
                pilzeToetenBakterienAb();
                alleLebewesenVermehrenSich();
                alleLebewesenAltern();
                lebewesen.trimToSize();
                warte(1);
            }
        }
     
        private void alleLebewesenAltern()
        {
            Lebewesen l;
            double wahrscheinlichkeit;
            for (int i=0; i<lebewesen.size(); i++)
            {
                l=lebewesen.get(i);
                l.altern();
                wahrscheinlichkeit=rand.nextDouble();
                if ((wahrscheinlichkeit<l.pSterbenGeben()))
                {
                    lebewesen.remove(i);
                }
            }
        }
     
        private void pilzeToetenBakterienAb()
        {
            Lebewesen l;
            for (int i=0; i<lebewesen.size(); i=i+1)
            {
                l=lebewesen.get(i);
                l.bakterienAbtoeten();
            }
        }
     
        private void alleLebewesenVermehrenSich()
        {
            Lebewesen l;
            double wahrscheinlichkeit;
            int anzahl=lebewesen.size();
            for (int i=0; i<anzahl; i++)
            {
                l=lebewesen.get(i);
                wahrscheinlichkeit=rand.nextDouble();
                if ((wahrscheinlichkeit<l.pVermehrungGeben()))
                {
                    l.vermehren();
                }
            }
        }
     
        private int anzahlLebewesen()
        {
            int l;
            l=lebewesen.size();
            return l;
        }
     
        private void warte(int ms)
        {
            try
            {
                TimeUnit.SECONDS.sleep(ms);
            }
            catch (Exception e)
            {
                //nichts tun
            }
        }
    }

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    Default Re: TimeUnit.SECONDS.sleep(x) stops simulation

    Looks like you set default thread to sleep. So it's normal. How do you call the warte(int ms) ?

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    Default Re: TimeUnit.SECONDS.sleep(x) stops simulation

    Quote Originally Posted by trod View Post
    Looks like you set default thread to sleep. So it's normal. How do you call the warte(int ms) ?
    I call it with the method simulationStarten()

        public void simulationStarten()
        {
            int dauer=999999999;
            Darstellung d=new Darstellung(lebewesen);
            lebewesenErzeugen(1,1);
            for (int i=0; i<dauer; i++)
            {  
                pilzeToetenBakterienAb();
                alleLebewesenVermehrenSich();
                alleLebewesenAltern();
                lebewesen.trimToSize();
                warte(1);
            }
        }

    Therer I insert "1" so it waits 1s per loop. But somehow the loop just stops without any error when it hits this line.

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    Default Re: TimeUnit.SECONDS.sleep(x) stops simulation

    But dauer (duration?) is 999999999.

    Then you are running a for loop from 0 to 999999999 and it hangs for 1 second each iteration. I am guessing that 31.6888 years to complete the loop isn't the desired behavior.
    Last edited by ChristopherLowe; January 20th, 2014 at 11:45 AM. Reason: type-o

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    Default Re: TimeUnit.SECONDS.sleep(x) stops simulation

    Yea I just wanted that the simulation gets to its end. Means that every bacteria is being removed by the penecilin. But that doesnt occur the "error". When I write the
    method simulationStarten() like this:

    public void simulationStarten(int dauer)
        {
            Darstellung d=new Darstellung(lebewesen);
            lebewesenErzeugen(1,1);
            for (int i=0; i<dauer; i++)
            {  
                pilzeToetenBakterienAb();
                alleLebewesenVermehrenSich();
                alleLebewesenAltern();
                lebewesen.trimToSize();
                warte(1);
            }
        }

    the loop still ends without any error after it hits the method warte(int ms)

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