Stack.java

package ds.stack.regular;

public class Stack<Item> {
    private Node<Item> top = null;
    private int length = 0;


    /* Push an item onto the stack */
    public void push(Item item) {
        Node<Item> newNode = new Node<Item>();  // 1
        newNode.data = item;                    // 1
        newNode.next = top;                     // 2
        top = newNode;                          // 3
        length++;                               // 4
    }

    /* Check if the stack is empty */
    public boolean isEmpty() {
        return top == null;
    }

    /* Remove the top item from the stack, and return its data */
    public Item pop() {
        if (isEmpty()) {                                                    // 1
            throw new IndexOutOfBoundsException("The stack is empty.");     // 1
        }                                                                   // 1
        Item item = top.data;                                               // 2
        top = top.next;                                                     // 3
        length--;                                                           // 4
        return item;                                                        // 5
    }

    /* Return the current size of the stack */
    public int size() {
        return length;
    }
}