stack.java

The Funambol J2ME Mail Client aims to be a light, easy to use, free email client for J2ME devices.

/*
 * Copyright (C) 2006-2007 Funambol
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package com.funambol.mailclient.ui.controller;

import javax.microedition.lcdui.*;

/**
 * This class can be used to implement a stack of displayable screens.
 * It provides a function to go forward and back with the screens
 * of the UI
 */
public class Stack {
    
    /** Array of screens in the Stack
     *  Configure the right dimension of the stack considering the depth of the
     *  UI workflow: i.e. how many back commands do we need to go back from the
     *  leaf to the root of the UI?
     */
    private Displayable [] screens;
    private final int STACK_DEPTH=20;
    
    public Stack() {
        screens = new Displayable [STACK_DEPTH];
    }
    
    /**
     * Insert a screen in the Stack
     * @param d Displayable screen to put in the Stack in order to retrieve later
     */
    public void push(Displayable d) {
        
        if ((d!=null) && (d!=screens[0]) && !(d instanceof Alert)) {
            for (int i=STACK_DEPTH-1; i>0;i--) {
                screens[i] = screens[i-1];
            }
            screens[0] = d;
        }
    }
    
    /**
     * Get the latest Screen to go back
     * @return Returns the Displayable Screen to display to go back
     */
    public Displayable pop() {
        Displayable result = screens[0];
        for (int i=0; i<STACK_DEPTH-2;i++) {
            screens[i] = screens[i+1];
        }
        screens[STACK_DEPTH-1] = null;
        return result;
    }
    
    public Displayable peek() {
        try {
            return screens[0];
        } catch (NullPointerException ex) {
            return null;
        }
    }

    public void clear() {
        for (int i=0; i<STACK_DEPTH-2;i++) {
            screens[i] = null;
        }    
    }
}