Sequence.java

Below is the syntax highlighted version of Sequence.java from §4.3 Stacks and Queues.

/******************************************************************************
 *  Compilation:  javac Sequence.java
 *  Execution:    java Sequence
 *
 *  A sequence implemented with a linked list. The elements are stored
 *  (and iterated over) in the same order that they are inserted.
 *
 *  % java Sequence
 *  This
 *  is
 *  a
 *  test.
 *
 *  This
 *  is
 *  a
 *  test.
 *
 ******************************************************************************/

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

public class Sequence<Item> implements Iterable<Item> {
    private int n;            // number of elements on list
    private Node first;       // first element
    private Node last;        // last element

    // linked list node helper data type
    private class Node {
        private Item item;
        private Node next;
        Node(Item item, Node next) {
            this.item = item;
            this.next = next;
        }
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return n;
    }

    // add item to the end of the list
    public void add(Item item) {
        Node x = new Node(item, null);
        if (isEmpty()) first = x;
        else last.next = x;
        last = x;
        n++;
    }

    //// prepend item to the beginning of the list
    // public void addFirst(Item item) {
    //    first = new Node(item, first);
    //    if (isEmpty()) last = first;
    //    n++;
    //}

    public Iterator<Item> iterator()  { return new SeqIterator();  }

    // an iterator, doesn't implement remove() since it's optional
    private class SeqIterator implements Iterator<Item> {
        private Node 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;
        }
    }



    // a test client
    public static void main(String[] args) {
        String sentence = "This is a test";
        String[] words = sentence.split(" ");
        Sequence<String> sequence = new Sequence<String>();
        for (int i = 0; i < words.length; i++) {
            sequence.add(words[i]);
        }

        // try out the iterator
        Iterator<String> i = sequence.iterator();
        while (i.hasNext()) {
            StdOut.println(i.next());
        }
        StdOut.println();

        // do it again, this time using Java's foreach syntax
        for (String s : sequence) {
            StdOut.println(s);
        }
        StdOut.println();
    }
}