ArrayStack.java

/*
 *  Copyright (C) 2014  Alfons Wirtz  
 *   website www.freerouting.net
 *
 *   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 3 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 at <http://www.gnu.org/licenses/> 
 *   for more details.
 *
 * ArrayStack.java
 *
 * Created on 11. Maerz 2006, 06:52
 *
 */

package datastructures;

@SuppressWarnings("unchecked")

/**
 * Implementation of a stack as an array.
 *
 * @author Alfons Wirtz
 */
public class ArrayStack <p_element_type>
{
    /**
     * Creates a new instance of ArrayStack with an initial maximal capacity  for p_max_stack_depth elements.
     */
    public ArrayStack(int p_max_stack_depth)
    {
        node_arr = (p_element_type [] ) new Object [p_max_stack_depth];
    }
    
    /**
     * Sets the stack to empty.
     */
    public void reset()
    {
        level = -1;
    }
    
    /**
     *  Pushed p_element onto the stack.
     */
    public void push(p_element_type p_element)
    {
        
        ++level;
        
        if (level >= node_arr.length)
        {
            reallocate();
        }
        
        node_arr[level] = p_element;
    }
    
    /**
     * Pops the next element from the top of the stack.
     * Returns null, if the stack is exhausted.
     */
    public p_element_type pop()
    {
        if (level < 0)
        {
            return null;
        }
        p_element_type result = node_arr[level];
        --level;
        return result;
    }
    
    private void reallocate()
    {
        p_element_type [] new_arr = (p_element_type [] ) new Object[4 * this.node_arr.length];
        System.arraycopy(node_arr, 0, new_arr, 0, node_arr.length);
        this.node_arr = new_arr;
    }
    
    private int level = -1;
    
    private p_element_type[] node_arr ;
}