Stack (ADT)

An instance of the stack data structure is a sequence of elements (objects) with one end designated as the top of the stack:

$$E_1,E_2,E_3,\dots ,E_n$$

Main stack operations (LIFO):

• push(e): insert element $e$ at the top of the stack
• pop(): remove and return the element at the top of the stack Throws an error if stack is empty.

Additional stack operations:

• top(): return the top element in the stack without removing it Throws an error if stack is empty.
• size(): return the number of elements stored
• isEmpty(): check if the stack is empty

Java Stack Interface

Below is a Java interface according to our stack ADT:

public interface Stack<E> {
	public void push(E element);
	public E pop() throws EmptyStackException;
	public E top() throws EmptyStackException;
	public int size();
	public boolean isEmpty();
}