ResizingArrayBag.java

Below is the syntax highlighted version of ResizingArrayBag.java.

/******************************************************************************
 *  Compilation:  javac ResizingArrayBag.java
 *  Execution:    java ResizingArrayBag
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Bag implementation with a resizing array.
 *
 ******************************************************************************/

package edu.princeton.cs.algs4;

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

/**
 *  The {@code ResizingArrayBag} 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 resizing array.
 *  See {@link LinkedBag} for a version that uses a singly linked list.
 *  The <em>add</em> operation takes constant amortized time; the
 *  <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 ResizingArrayBag<Item> implements Iterable<Item> {
    // initial capacity of underlying resizing array
    private static final int INIT_CAPACITY = 8;

    private Item[] a;         // array of items
    private int n;            // number of elements on bag

    /**
     * Initializes an empty bag.
     */
    public ResizingArrayBag() {
        a = (Item[]) new Object[INIT_CAPACITY];
        n = 0;
    }

    /**
     * Is this bag empty?
     * @return true if this bag is empty; false otherwise
     */
    public boolean isEmpty() {
        return n == 0;
    }

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

    // resize the underlying array holding the elements
    private void resize(int capacity) {
        assert capacity >= n;
        Item[] copy = (Item[]) new Object[capacity];
        for (int i = 0; i < n; i++)
            copy[i] = a[i];
        a = copy;
    }

    /**
     * Adds the item to this bag.
     * @param item the item to add to this bag
     */
    public void add(Item item) {
        if (n == a.length) resize(2*a.length);    // double size of array if necessary
        a[n++] = item;                            // add item
    }


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

    // an array iterator
    private class ArrayIterator implements Iterator<Item> {
        private int i = 0;

        public boolean hasNext() {
            return i < n;
        }

        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            return a[i++];
        }
    }

    /**
     * Unit tests the {@code ResizingArrayBag} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        ResizingArrayBag<String> bag = new ResizingArrayBag<String>();
        bag.add("Hello");
        bag.add("World");
        bag.add("how");
        bag.add("are");
        bag.add("you");

        for (String s : bag)
            StdOut.println(s);
    }

}

/******************************************************************************
 *  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.
 ******************************************************************************/