//********************************************************************
//  StackViewer.java       Author: Sophie Quigley
//
//  Class StackViewer shows a transparent stack and its contents.
//  This class is intended to be subclassed.
//
//********************************************************************

public class StackViewer
{
    // The stack viewer keeps a reference to the transparent stack inside its visible stack.
    // It will interact directly with it to get stack elements for its display.
    protected TransparentStack stack;

    // When a new stackviewer for a visible stack is created, 
    // it is added to the list of viewers for that visible stack
    public StackViewer (VisibleStack stack)
    {
        stack.addViewer(this);
    }

    // After a viewer has been added to a visible stack's list of viewers,it is initialized.
    // At the very least the transparent stack reference is initialized.
    // This is why initialize must be invoked once before the other methods,
    // and why the functionality below should be duplicated if this method is overridden.
    public void initialize (TransparentStack stack)
    {
        this.stack = stack;
    }
    
    // Display which displays the stack should be overridden in the subclasses.
    public void display()
    {
        int size = stack.currentSize();
        if (size == 0)
            System.out.println("The stack is empty");
        else
            System.out.println("The stack has "+size+ " elements.  The top is "+stack.top().toString());
    }

    // ShowTop simply shows the top of the stack.
    public void showTop()
    {
        if (stack.empty())
            System.out.println("There is no top because the stack is empty");
        else
            System.out.println("The top of the stack is "+stack.top().toString());
    }

}