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Thread: Null Pointer Exception?

  1. #1
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    Default Null Pointer Exception?

    I am getting a null pointer exception and can not figure out what I'm missing here. Does anyone have any idea what I'm missing?

    import javax.swing.*;

    public class Truck{

    public int [] choice;
    public String [] model;
    public int [] cd;
    public int [] speaker;
    public int [] cost;

    public int choiceCount;
    public int modelCount;
    public int cdCount;
    public int speakerCount;
    public int costCount;

    public String summaryOutput;

    public void Truck(){

    choice = new int[100];
    model = new String[100];
    cd = new int[100];
    speaker = new int[100];
    cost = new int[100];

    choiceCount = 0;
    modelCount = 0;
    cdCount = 0;
    speakerCount = 0;
    costCount = 0;

    summaryOutput = "";

    }//end Truck method

    public String WithSpeakerSummary(){

    for(int i = 0; i < choiceCount; i++){

    if(choice[i] == 1){

    summaryOutput += "Cars with Stereos:/nModel: " + model[i] +
    "/nCost: " + cost[i] +
    "/n# CDs: " + cd[i] +
    "/n# Speakers: " + speaker[i] +
    "/n/n";

    }//end if statement

    }//end


    return summaryOutput;
    }//end Summary method

    public String WithOutSpeakerSummary(){

    for(int i = 0; i < choiceCount; i++){

    if(choice[i] == 0){

    summaryOutput += "Cars with Stereos:/nModel: " + model[i] +
    "/nCost: " + cost[i] +
    "/n/n";

    }//end if statement

    }//end


    return summaryOutput;
    }//end Summary method

    public void addWithChoice(int w){

    choice[choiceCount++] = w;

    }//end addWithChoice method

    public void addWithoutChoice(int wo){

    choice[choiceCount++] = wo;

    }//end addWithoutChoice method

    public void addModel(String m){

    model[modelCount++] = m;

    }//end addModel method

    public void addCD(int c){

    cd[cdCount++] = c;

    }//end addModel method

    public void addSpeaker(int s){

    speaker[speakerCount++] = s;

    }//end addModel method

    public void addCost(int t){

    cost[costCount++] = t;

    }//end addModel method

    }//end Truck super class

    import javax.swing.*;

    public class TruckWithStereo extends Truck{

    public static void main(String[] args){


    int aChoice = 0;
    String aModel = "";
    int aCD = 0;
    int aSpeaker = 0;
    int aCost = 0;

    Truck tObject = new Truck();

    do{

    while(JOptionPane.showConfirmDialog(null, "Does this car have a stereo?") == JOptionPane.YES_OPTION){

    //with speakers
    aChoice = 1;
    tObject.addWithChoice(aChoice);

    aModel = JOptionPane.showInputDialog("Model of car?");
    tObject.addModel(aModel);

    aCD = Integer.parseInt(JOptionPane.showInputDialog("How many CDs in the player?"));
    tObject.addCD(aCD);

    aSpeaker = Integer.parseInt(JOptionPane.showInputDialog("How many speakers in the car?"));
    tObject.addSpeaker(aSpeaker);

    aCost = Integer.parseInt(JOptionPane.showInputDialog("Cost of car?"));
    tObject.addCost(aCost);

    }//end YES Option while loop


    while(JOptionPane.showConfirmDialog(null, "Does this car have a stereo?") == JOptionPane.NO_OPTION){

    //without speakers
    aChoice = 0;
    tObject.addWithoutChoice(aChoice);

    aModel = JOptionPane.showInputDialog("Model of car?");
    tObject.addModel(aModel);

    aCost = Integer.parseInt(JOptionPane.showInputDialog("Cost of car?"));
    tObject.addCost(aCost);

    }//end NO Option while loop

    }while(JOptionPane.showConfirmDialog(null, "Still looking for cars?") == JOptionPane.YES_OPTION);//end do-while loop



    if(JOptionPane.showConfirmDialog(null, "Do you want to see cars with stereos?") == JOptionPane.YES_OPTION){

    tObject.WithSpeakerSummary();

    }//end YES Option while loop


    else if(JOptionPane.showConfirmDialog(null, "Do you want to see cars with stereos?") == JOptionPane.NO_OPTION){

    tObject.WithOutSpeakerSummary();

    }//end NO Option while loop


    }//end main method



    }//end TruckWithStereo subclass


  2. #2
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    Default Re: Null Pointer Exception?

    The error message will tell on which line it occurs. Go to that line and examine all your variables to determine which is null. Then make sure it is not null before you try to use it.
    Improving the world one idiot at a time!

  3. #3
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    Default Re: Null Pointer Exception?

    I did not realize that. I checked the lines, but still can not figure out what the problem is. I have initialized the variables.

    The first is on line 29 in the TruckWithStereo class

    tObject.addWithChoice(aChoice);
    The second is on line 85 in the Truck class

    choice[choiceCount++] = w;

  4. #4
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    Default Re: Null Pointer Exception?

    Copy and paste the exact error message.
    Improving the world one idiot at a time!

  5. #5
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    Default Re: Null Pointer Exception?

    Oh sorry here is the entire thing. If you are wondering about the IT206.labbassignments.lab2assignment. that's the package that I have the two files in.

    Exception in thread "main" java.lang.NullPointerException
    at IT206.labassignments.lab2assignment.Truck.addWithC hoice(Truck.java:85)
    at IT206.labassignments.lab2assignment.TruckWithStere o.main(TruckWithStereo.java:29)
    Java Result: 1

  6. #6
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    Default Re: Null Pointer Exception?

    The error is on line 85 of the Truck class which according to you is: choice[choiceCount++] = w;
    That means that the choice variable is null and has not been instantiated. "But it has been in the Truck constructor" I here you cry. Well you might want to check that. Hint: methods and constructors are different things.
    Improving the world one idiot at a time!

  7. The Following User Says Thank You to Junky For This Useful Post:

    Mr.777 (November 16th, 2011)

  8. #7
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    Default

    Uhhh do you think you could give a better hint then that? haha

    I apologize this has been driving me nuts and I am resorting to the forum because I'm hopelessly lost now.

  9. #8
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    Default Re: Null Pointer Exception?

    I almost pointed you directly to the problem. Where is the constructor in the Truck class? It doesn't have one.
    Improving the world one idiot at a time!

  10. #9
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    Default

    So the Truck method I created is not serving as a Truck constructor in that class then?

  11. #10
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    Default Re: Null Pointer Exception?

    Of course not since methods are method not constructors. If you do not understand the difference then you need to do some revision.
    Improving the world one idiot at a time!

  12. #11
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    Default

    After reading your last post I did do some reviewing and realized what I did to cause those errors. thanks for the help! turns out there were more that arose but I got all the bugs out finally.

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