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Thread: Using an array which is in a superclass

  1. #1
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    Default Using an array which is in a superclass

    Ok so I have these two classes: Book and Encyclopedia. I want to create a method in Encyclopedia. I want it to modify an array which is an object in Book class. I'm not allowed to take the array as a method input like this: public void MethodName(Book [] a, String ...){ Instead, I have to find a way to call that array in the method and modify one of the elements in it. I know how to modify the element, just I don't know how to call the array in a superclass to a subclass. Thanks.


  2. #2
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    Default Re: Using an array which is in a superclass

    In order to directly edit a variable from a superclass, you need to set it protected. Here is the gist of the modifiers:
    • public: Anyone can use the variable.
    • no modifier: Anyone in this package can use this variable.
    • protected: Sub-classes can use this variable
    • private: Only this class can use this variable


    So let's say you have a "Beverage" and a "Soda" class. Where Soda extends Beverage

    Beverage:
    /**
     * A classic beverage with a name. Not inheritantly mutable.
     */
    public class Beverage
    {
      //Variables
      /**
       * The name of the Beverage
       */
      protected String name;
      //Constructors
      /**
       * Specifies the name of the beverage.
       * @param nameOfBeverage The name of the beverage
       */
      public Beverage(String nameOfBeverage)
      {
        name = nameOfBeverage;
      }
      //Methods
      /**
       * @return name of the beverage
       */
      public String getName()
      {
        return name;
      }
    }
    Soda:
    /**
     * Extension of Beverage whom's name is either Coke, Dr. Pepper, or Root Beer.
     */
    public class Soda extends Beverage
    {
      //Constructors
      /**
       * Create a beverage of the specified type. 0, 1 and 2 being Coke, Dr. Pepper and Root Beer respectively.
       */
      public Soda(int type)
      {
        /* First get the String value of the type.  I do believe it is only possible to call
         * the super-classes constructor as the first line of code, so we modifiy the variable
         * directly.
         */
        String name = null;
        switch(type)
        {
          case 0:
            name = "Coke";
            break;
          case 1:
            name = "Dr. Pepper";
            break;
          case 2:
            name = "Root Beer";
            break;
        }
        //Call our parent classes variable "name" and sets it.
        super.name = name;
      }
    }

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    Default Re: Using an array which is in a superclass

    This thread has been cross posted here:

    http://www.java-forums.org/new-java/50499-using-array-superclass.html

    Although cross posting is allowed, for everyone's benefit, please read:

    Java Programming Forums Cross Posting Rules

    The Problems With Cross Posting


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