/* use a stack to push and pop displayable objects which will include
* public void pushDisplayable(Displayable)
* public void popDisplayable()
* public void home() methods
*/
/**************************************
* Source & Further Reading: J. W. Muchow (2002), Core J2ME Technology & MIDP, Sun MICROSYSTEMS
***************************************/


import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
import java.util.*;

public class DisplayManager extends Stack {

  private Display display; // refer to a Display object
  private Displayable mainDisplayable; // the main Displayable for the MIDlet
  private Alert alSE; // Any stack error to be displyed by this Alert object

  // MyDisplayManager Constructor

  public DisplayManager(Display display, Displayable mainDisplayable){
    // You can only display one Displayable object per MIdlet, "this"

    this.display = display;
    this.mainDisplayable = mainDisplayable;

    // create the alert display if an error occurs
    alSE = new Alert("Unable to Perform Task"); // Stack error Alert
    alSE.setTimeout(Alert.FOREVER); // Modal
  }

  // Pop displayable from stack and activate
public void popDisplayable() {
 // if stack is not empty show next displayable
 if(empty() == false)
   display.setCurrent((Displayable) pop());
   else
     // if error occurs alert, and set the main displayable active
  display.setCurrent(alSE, mainDisplayable);
}


  /* Push the displayable object onto stack and set the passed in displayable
      as active */
  public void pushDisplayable(Displayable newDisplayable){
    push(display.getCurrent());
    display.setCurrent(newDisplayable);
  }

  // Return to the main displayable object

  public void home(){
    while (elementCount > 1) {
      pop();
      display.setCurrent(mainDisplayable);
    }
  }
}