package closedlist;

import openlist.OpenList;

/**
 * A OLStack constructed using an OpenList
 * @author Robert Keller
 */
public class OLStack
{
/**
 * contents contains the objects in the stack, for newest to oldest.
 */
OpenList contents;

    /**
     * Construct an empty stack.
     */

    public OLStack()
      {
        clear();
      }

    
    /**
     * Push the newest value onto the stack
     * @param value 
     */
    
    public void push(Object value)
      {
        contents = OpenList.cons(value, contents);
      }
    
    
    /**
     * Remove the newest value from the stack and return it.
     * @return the newest value that was on the stack.
     */
    
    public Object pop()
      {
        Object result = contents.first();
        contents = contents.rest();
        return result;
      }
    
    /**
     * Return true if the stack is empty, false otherwise.
     * @return 
     */
    
    public boolean isEmpty()
      {
        return contents.isEmpty();
      }
    
    /**
     * Return true if the stack is non-empty, false otherwise.
     * @return 
     */
    
    public boolean nonEmpty()
      {
        return contents.nonEmpty();
      }
    
    
    /**
     * Clear all elements from the stack
     */
    public final void clear()
      {
       contents = OpenList.nil;
      }
    
    /**
     * Test a stack crudely, by pushing on integers, then
     * popping and checking that the popped values agree with what is
     * expected.
     */
    
    public static void main(String arg[])
      {
        OLStack stack = new OLStack();
        
        int i;
        
        for( i = 0; i < 100; i++ )
          {
            stack.push(i);
          }
        
        while( stack.nonEmpty() )
          {
            int actual = (Integer)stack.pop();
            
            if( --i != actual )
              {
                System.out.println("Stack failed at " + i);
              }
          }
      }
}