Stack Implementations - Data Structures and Abstractions with Java - page 147

6.16

An outline of the class. The class that implements the stack begins by declaring a vector as a data
field and allocating the vector in its constructors. Thus, we must provide an import statement prior
to the class definition. Listing 6-3 outlines our class.

LISTING 6-3

An outline of a vector-based implementation of the ADT stack

import java.util.Vector;
/**

A class of stacks whose entries are stored in a vector.
@author Frank M. Carrano

*/
public class VectorStack<T> implements StackInterface<T>
{

private Vector<T> stack; // last element is the top entry in stack
private static final int DEFAULT_INITIAL_CAPACITY = 50;

public VectorStack()
{

this (DEFAULT_INITIAL_CAPACITY);
} // end default constructor

public VectorStack( int initialCapacity)
{

stack = new Vector<T>(initialCapacity); // size doubles as needed
} // end constructor

< Implementations of the stack operations go here. >
. . .
} // end VectorStack

6.17

Adding to the top. We use Vector 's method add to add an entry to the end of the vector, that is, to
the top of the stack.

public void push(T newEntry)
{

stack.add(newEntry);
} // end push

6.18

Retrieving the top. We retrieve the stack's top entry by using Vector 's method lastElement .
public T peek()
{

T top = null ;
if (!isEmpty())
top = stack.lastElement();
return top;
} // end peek