LinkedBag.java

Below is the syntax highlighted version of LinkedBag.java from §1.3 Stacks and Queues.

/******************************************************************************
 *  Compilation:  javac LinkedBag.java
 *  Execution:    java LinkedBag < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  A generic bag or multiset, implemented using a singly linked list.
 *
 *  % more tobe.txt
 *  to be or not to - be - - that - - - is
 *
 *  % java LinkedBag < tobe.txt
 *  size of bag = 14
 *  is
 *  -
 *  -
 *  -
 *  that
 *  -
 *  -
 *  be
 *  -
 *  to
 *  not
 *  or
 *  be
 *  to
 *
 ******************************************************************************/

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 *  The {@code LinkedBag} class represents a bag (or multiset) of
 *  generic items. It supports insertion and iterating over the
 *  items in arbitrary order.
 *  <p>
 *  This implementation uses a singly linked list with a non-static nested class Node.
 *  See {@link Bag} for a version that uses a static nested class.
 *  The <em>add</em>, <em>isEmpty</em>, and <em>size</em> operations
 *  take constant time. Iteration takes time proportional to the number of items.
 *  <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
 */
public class LinkedBag<Item> implements Iterable<Item> {
    private Node first;    // beginning of bag
    private int n;         // number of elements in bag

    // helper linked list class
    private class Node {
        private Item item;
        private Node next;
    }

    /**
     * Initializes an empty bag.
     */
    public LinkedBag() {
        first = null;
        n = 0;
    }

    /**
     * Is this bag empty?
     * @return true if this bag is empty; false otherwise
     */
    public boolean isEmpty() {
        return first == null;
    }

    /**
     * Returns the number of items in this bag.
     * @return the number of items in this bag
     */
    public int size() {
        return n;
    }

    /**
     * Adds the item to this bag.
     * @param item the item to add to this bag
     */
    public void add(Item item) {
        Node oldfirst = first;
        first = new Node();
        first.item = item;
        first.next = oldfirst;
        n++;
    }


    /**
     * Returns an iterator that iterates over the items in the bag.
     */
    public Iterator<Item> iterator()  {
        return new LinkedIterator();
    }

    // an iterator over a linked list
    private class LinkedIterator implements Iterator<Item> {
        private Node current;

        // creates a new iterator
        public LinkedIterator() {
            current = first;
        }

        // is there a next item in the iterator?
        public boolean hasNext() {
            return current != null;
        }

        // returns the next item in the iterator (and advances the iterator)
        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            Item item = current.item;
            current = current.next;
            return item;
        }
    }

    /**
     * Unit tests the {@code LinkedBag} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        LinkedBag<String> bag = new LinkedBag<String>();
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            bag.add(item);
        }

        StdOut.println("size of bag = " + bag.size());
        for (String s : bag) {
            StdOut.println(s);
        }
    }


}