// Fig. 21.7: Stack.java
// Stack generic class declaration.
import java.util.ArrayList;

public class Stack< T >  
{
   private ArrayList< T > elements; // ArrayList stores stack elements

   // no-argument constructor creates a stack of the default size
   public Stack()
   {
      this( 10 ); // default stack size
   } // end no-argument Stack constructor
   
   // constructor creates a stack of the specified number of elements
   public Stack( int capacity )
   {
      int initCapacity = capacity > 0 ? capacity : 10; // validate
      elements = new ArrayList< T >( initCapacity ); // create ArrayList
   } // end one-argument Stack constructor

   // push element onto stack
   public void push( T pushValue )
   {
      elements.add( pushValue ); // place pushValue on Stack
   } // end method push

   // return the top element if not empty; else throw EmptyStackException
   public T pop()
   {
      if ( elements.isEmpty() ) // if stack is empty
         throw new EmptyStackException( "Stack is empty, cannot pop" );

      // remove and return top element of Stack
      return elements.remove( elements.size() - 1 ); 
   } // end method pop
} // end class Stack< T >

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