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Thread: Problem with Arrays

  1. #1
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    Unhappy Problem with Arrays

    Hello,
    Okay I'm stuck here, and have been for a while I've searched everything I can and still can't seem to find out what is going on. Alright I have an Object Called Aircraft. The Object Airplane has the following Fields Aircraft_Id (String), Aircraft_Type (String), Index (BigDecimal), BOW (Int). I have two different Constructors, has nothing passed to it and sets all the fields to an default Value, and a second one that requires ALL fields be supplied.

    When I try to set a Field (i.e. Airplane.Aircraft_Id = "Some Aircraft Id") everything seems to work just great, I can set it, and later retrive it.
    Unforuntatly I don't find see having 100 differenct aircraft Instances as very efficent so I wanted to create an array of Airplanes.

    static public Airplane Aircraft[] = new Airplane[100];

    Everything Seems to work fine until I try to set a field

    Aircraft[1].Aircraft_Id = "Some Aircraft Id";

    This causes my program to crash.

    A Side note this is to be run on Android however, this appears to be a failure in my understanding of basic Java is the reason why I'm here and not an an android developers forum.

    Thank You for your Help


  2. #2
    Administrator copeg's Avatar
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    Default Re: Problem with Arrays

    This causes my program to crash.
    It helps to define 'crash'...eg the exception you receive. Did you instantiate the members of the array? You can create an array of Objects, but unless you actually instantiate these they will by default be null

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    Default Re: Problem with Arrays

    Quote Originally Posted by copeg View Post
    It helps to define 'crash'...eg the exception you receive. Did you instantiate the members of the array? You can create an array of Objects, but unless you actually instantiate these they will by default be null
    I would define Crash as the Program ends.

    I was wondering if you had to create each member of the array or not, but i would assume that they would have been all created simply throught the act of creating the array. How does one go about creating an istance of the object with in the array?

  4. #4
    Administrator copeg's Avatar
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    Default Re: Problem with Arrays

    Did you see the console? Do you know what an exception is?
    Yes you have to instantiate members of the array. See the following, which defines an array with 1 element not instantiated, and which will throw a NullPointerException because of this
     
    String[] myString = new String[2];
    myString[0] = "My String";//instantiate the first element
    if ( myString[1].equals(myString[1] ) {
       System.out.println("The above line will throw a NullPointerException");
    }

  5. The Following User Says Thank You to copeg For This Useful Post:

    dashpilot (March 6th, 2012)

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    Default Re: Problem with Arrays

    Okay I got it figured out. As far as I can tell there isn't a console for Android Apps, or at least not one that tells you anything.

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