Thread: 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.