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Thread: inheritance - why its not working?

  1. #1
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    Default inheritance - why its not working?

    Hi,
    I wrote a class named box With a variable named volume.
    This is the first class, very simple:


    package inheritance_Ex_2;
     
    public class Box {
    	private String Label;
    	private double volume;
     
    	public Box(String label) {
    		super();
    		Label = label;
    		this.volume = volume;
    	}
     
    	public void Volume(double volume) {
    		this.volume = volume;


    Then I wrote a class that inherite from Box and Sets a value to volume:


    package inheritance_Ex_2;
     
    public class PlasticBox extends Box {
    	private int length;
    	private int wigth;
    	private int hight;
     
    	public PlasticBox(String label, int length, int wigth, int hight) {
    		super(label);
    		this.length = length;
    		this.wigth = wigth;
    		this.hight = hight;
    	}
     
    	public void setVolume () {
    		Volume(getLength() * getWigth() * getHight());
    	}

    But when I write main class and try to use the setVolume function its not working:


     
    package inheritance_Ex_2;
     
    public class BoxProgram {
     
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		Box plastic1 = new PlasticBox("grapes", 4, 4, 4);
     
    		plastic1.setVolume();
     
    		plastic1.BoxData();
     
    	}
     
    }




    its write me that that there is no "setVolume" in Box class.
    its right, there is no "setVolume" in Box class but there is "setVolume" in PlasticBox class.
    I suppose that the problam is in this line:

    Box plastic1 = new PlasticBox("grapes", 4, 4, 4);


    and when I chage it to - PlasticBox plastic1 = new PlasticBox("grapes", 4, 4, 4);
    it fix the problem but I dont understand why.



  2. #2
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    Default Re: inheritance - why its not working?

    It tells you that because the setVolume() class is in the subclass, not the inherited class of Box. When you assign a instance of a subclass to its parent class, the only methods visible are those of the parent class.

    Regards,
    Jim

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