StackInterface.java

/**
    An interface for the ADT stack.
*/

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 void push(T newEntry);
  
  /** Removes and returns this stack's top entry.
      @return either the object at the top of the
      stack or, if the stack is empty before the
      operation, return null */
  public T pop();
  
  /** Retrieves this stack's top entry.
      @return either 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 iff the stack is empty */
  public boolean isEmpty();
  
  /** Removes all entries from this stack */
  public void clear();
  
} // end StackInterface