Below is the syntax highlighted version of Stack.java.
/****************************************************************************** * Compilation: javac Stack.java * Execution: java Stack < input.txt * Dependencies: StdIn.java StdOut.java * Data files: https://algs4.cs.princeton.edu/13stacks/tobe.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) * ******************************************************************************/ package edu.princeton.cs.algs4; import java.util.Iterator; import java.util.NoSuchElementException; /** * The {@code Stack} class represents a last-in-first-out (LIFO) stack of generic items. * It supports the usual <em>push</em> and <em>pop</em> operations, along with methods * for peeking at the top item, testing if the stack is empty, and iterating through * the items in LIFO order. * <p> * 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. * See {@link ResizingArrayStack} for a version that uses a resizing array. * The <em>push</em>, <em>pop</em>, <em>peek</em>, <em>size</em>, and <em>is-empty</em> * operations all take constant time in the worst case. * <p> * For additional documentation, * see <a href="https://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of * <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne * * @param <Item> the generic type each item in this stack */ public class Stack<Item> implements Iterable<Item> { private Node<Item> first; // top of stack private int n; // size of the stack // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Initializes an empty stack. */ public Stack() { first = null; n = 0; } /** * Returns true if this stack is empty. * * @return true if this stack is empty; false otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this stack. * * @return the number of items in this stack */ public int size() { return n; } /** * Adds the item to this stack. * * @param item the item to add */ public void push(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); 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 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 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 this stack in LIFO order, separated by spaces */ public String toString() { StringBuilder s = new StringBuilder(); for (Item item : this) { s.append(item); s.append(' '); } 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<Item> iterator() { return new LinkedIterator(first); } // the iterator private class LinkedIterator implements Iterator<Item> { private Node<Item> current; public LinkedIterator(Node<Item> first) { current = first; } // is there a next item? public boolean hasNext() { return current != null; } // returns the next item public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the {@code Stack} data type. * * @param args the command-line arguments */ public static void main(String[] args) { Stack<String> stack = new Stack<String>(); while (!StdIn.isEmpty()) { String item = StdIn.readString(); if (!item.equals("-")) stack.push(item); else if (!stack.isEmpty()) StdOut.print(stack.pop() + " "); } StdOut.println("(" + stack.size() + " left on stack)"); } } /****************************************************************************** * Copyright 2002-2022, Robert Sedgewick and Kevin Wayne. * * This file is part of algs4.jar, which accompanies the textbook * * Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne, * Addison-Wesley Professional, 2011, ISBN 0-321-57351-X. * http://algs4.cs.princeton.edu * * * algs4.jar is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * algs4.jar is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with algs4.jar. If not, see http://www.gnu.org/licenses. ******************************************************************************/