StackInterface.java

package Graphs;

/**
   An interface for the ADT stack.
   @author Frank M. Carrano
   @author Timothy M. Henry
   @version 4.0
   UPDATED by C. Lee-Klawender
*/
public interface StackInterface<T>
{
   /** Adds a new entry to the top of this stack.
       @param newEntry  An object to be added to the stack. */
   public boolean push(T newEntry);

   /** Removes and returns this stack's top entry.
       @return  The object at the top of the stack.
                or null if the stack is empty*/
   public T pop();

   /** Retrieves this stack's top entry (without removing).
       @return  The object at the top of the stack.
                or null if the stack is empty. */
   public T peek();

   /** Detects whether this stack is empty.
       @return  True if the stack is empty. */
   public boolean isEmpty();
   /** Returns number of items in this stack
    @return: Number of items */
   public int size();

} // end StackInterface