Below is the syntax highlighted version of Stack.java from § Algorithms. Here is the Javadoc. /************************************************************************* * Compilation: javac Stack.java * Execution: java Stack < input.txt * * A generic stack, implemented using a singly-linked list. * Each stack element is of type Item. * * This version uses a static nested class Node (to save 8 bytes per * Node), whereas the version in the textbook uses a non-static nested * class (for simplicity). * * % more tobe.txt * to be or not to - be - - that - - - is * * % java Stack < tobe.txt * to be not that or be (2 left on stack) * *************************************************************************/ import java.util.Iterator; import java.util.NoSuchElementException; /** * The Stack class represents a last-in-first-out (LIFO) stack of generic items. * It supports the usual push and pop operations, along with methods * for peeking at the top item, testing if the stack is empty, and iterating through * the items in LIFO order. ** This implementation uses a singly-linked list with a static nested class for * linked-list nodes. See {@link LinkedStack} for the version from the * textbook that uses a non-static nested class. * The push, pop, peek, size, and is-empty * operations all take constant time in the worst case. *
* For additional documentation, see Section 1.3 of * Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class Stack
- implements Iterable
- { private int N; // size of the stack private Node
- first; // top of stack // helper linked list class private static class Node
- { private Item item; private Node
- next; } /** * Initializes an empty stack. */ public Stack() { first = null; N = 0; } /** * Is this stack empty? * @return true if this stack is empty; false otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in the stack. * @return the number of items in the stack */ public int size() { return N; } /** * Adds the item to this stack. * @param item the item to add */ public void push(Item item) { Node
- oldfirst = first; first = new Node
- (); first.item = item; first.next = oldfirst; N++; } /** * Removes and returns the item most recently added to this stack. * @return the item most recently added * @throws java.util.NoSuchElementException if this stack is empty */ public Item pop() { if (isEmpty()) throw new NoSuchElementException("Stack underflow"); Item item = first.item; // save item to return first = first.next; // delete first node N--; return item; // return the saved item } /** * Returns (but does not remove) the item most recently added to this stack. * @return the item most recently added to this stack * @throws java.util.NoSuchElementException if this stack is empty */ public Item peek() { if (isEmpty()) throw new NoSuchElementException("Stack underflow"); return first.item; } /** * Returns a string representation of this stack. * @return the sequence of items in the stack in LIFO order, separated by spaces */ public String toString() { StringBuilder s = new StringBuilder(); for (Item item : this) s.append(item + " "); return s.toString(); } /** * Returns an iterator to this stack that iterates through the items in LIFO order. * @return an iterator to this stack that iterates through the items in LIFO order. */ public Iterator
- iterator() { return new ListIterator
- (first); } // an iterator, doesn't implement remove() since it's optional private class ListIterator
- implements Iterator
- { private Node
- current; public ListIterator(Node
- first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the Stack data type. */ public static void main(String[] args) { Stack
s = new Stack (); while (!StdIn.isEmpty()) { String item = StdIn.readString(); if (!item.equals("-")) s.push(item); else if (!s.isEmpty()) StdOut.print(s.pop() + " "); } StdOut.println("(" + s.size() + " left on stack)"); } } Copyright © 2002–2010, Robert Sedgewick and Kevin Wayne. Last updated: Tue Sep 24 10:43:42 EDT 2013.