Observando o Código, o que ele quer fazer?

import java.util.ArrayList;

public class Stack< T >
{
private ArrayList< T > elements; 

	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 >

public class EmptyStackException extends RuntimeException
{
	public EmptyStackException()
	{
		this("Stack is empty");
	}
	public EmptyStackException(String message)
	{
		super(message);
	}
}

public class StackTest
 {
		public static void main( String[] args )
		{
		double[] doubleElements = { 1.1, 2.2, 3.3, 4.4, 5.5 };
		int[] integerElements = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

		// Create a Stack< Double > and a Stack< Integer >
		Stack< Double > doubleStack = new Stack< Double >( 5 );
		Stack< Integer > integerStack = new Stack< Integer >();

		// push elements of doubleElements onto doubleStack
		testPushDouble( doubleStack, doubleElements );
		testPopDouble( doubleStack ); // pop from doubleStack

		// push elements of integerElements onto integerStack
		testPushInteger( integerStack, integerElements );
		testPopInteger( integerStack ); // pop from integerStack
		} // end main

 
	// test push method with double stack
	private static void testPushDouble(
	Stack< Double > stack, double[] values )
	{
	System.out.println( "\nPushing elements onto doubleStack" );

	// push elements to Stack
	for ( double value : values )
	{
	System.out.printf( "%.1f ", value );
	stack.push( value ); // push onto doubleStack
	} // end for
	} // end method testPushDouble

	// test pop method with double stack
	private static void testPopDouble( Stack< Double > stack )
	{
	// pop elements from stack
	try
	{
	System.out.println( "\nPopping elements from doubleStack" );
	double popValue; // store element removed from stack

	// remove all elements from Stack
	while ( true )
	{
	popValue = stack.pop(); // pop from doubleStack
	System.out.printf( "%.1f ", popValue );
	} // end while
	} // end try
	catch( EmptyStackException emptyStackException )
	{
	System.err.println();
	emptyStackException.printStackTrace();
	} // end catch EmptyStackException
	} // end method testPopDouble

	// test push method with integer stack
	private static void testPushInteger(
	Stack< Integer > stack, int[] values )
	{
	System.out.println( "\nPushing elements onto integerStack" );

	// push elements to Stack
	for ( int value : values )
	{
	System.out.printf( "%d ", value );
	stack.push( value ); // push onto integerStack
	}//endfor
} // end method testPushInteger
 // test pop method with integer stack
private static void testPopInteger( Stack< Integer > stack ) {
			// pop elements from stack
			try
			{
			System.out.println( "\nPopping elements from integerStack" );
			int popValue; // store element removed from stack
			
			// remove all elements from Stack
			while ( true )
			{
			popValue = stack.pop(); // pop from intStack
			System.out.printf( "%d ",	popValue );
			} // end while
			} // end try
			catch( EmptyStackException emptyStackException )
			{
			System.err.println();
			emptyStackException.printStackTrace();
			} // end catch EmptyStackException
		}	// end method testPopInteger
	}	//	end class StackTest