ArrayBag.java

/*  * ArrayBag.java *  * Computer Science S-22 */ import java.util.*; /** * An simple implementation of a bag data structure that uses  * an array to store the items. */public class ArrayBag {    /**      * The array used to store the items in the bag.     */    private Object[] items;        /**      * The number of items in the bag.     */    private int numItems;        public static final int DEFAULT_MAX_SIZE = 50;        /**     * Constructor with no parameters - creates a new, empty ArrayBag with      * the default maximum size.     */    public ArrayBag() {        this.items = new Object[DEFAULT_MAX_SIZE];        this.numItems = 0;    }        /**      * A constructor that creates a new, empty ArrayBag with the specified     * maximum size.     */    public ArrayBag(int maxSize) {        if (maxSize <= 0) {            throw new IllegalArgumentException("maxSize must be > 0");        }        this.items = new Object[maxSize];        this.numItems = 0;    }        /**     * numItems - accessor method that returns the number of items      * in this ArrayBag.     */    public int numItems() {        return this.numItems;    }        /**      * add - adds the specified item to this ArrayBag. Returns true if there      * is room to add it, and false otherwise.     * Throws an IllegalArgumentException if the item is null.     */    public boolean add(Object item) {        if (item == null) {            throw new IllegalArgumentException("item must be non-null");        } else if (this.numItems == this.items.length) {            return false;    // no more room!        } else {            this.items[this.numItems] = item;            this.numItems++;            return true;        }    }        /**      * remove - removes one occurrence of the specified item (if any)     * from this ArrayBag.  Returns true on success and false if the     * specified item (i.e., an object equal to item) is not in this ArrayBag.     */    public boolean remove(Object item) {        for (int i = 0; i < this.numItems; i++) {            if (this.items[i].equals(item)) {                // Shift the remaining items left by one.                for (int j = i; j < this.numItems - 1; j++) {                    this.items[j] = this.items[j + 1];                }                this.items[this.numItems - 1] = null;                                this.numItems--;                return true;            }        }                return false;  // item not found    }        /**     * contains - returns true if the specified item is in the Bag, and     * false otherwise.     */    public boolean contains(Object item) {        for (int i = 0; i < this.numItems; i++) {            if (this.items[i].equals(item)) {                return true;            }        }                return false;    }        /**     * containsAll - does this ArrayBag contain all of the items in     * otherBag?  Returns false if otherBag is null or empty.      */    public boolean containsAll(ArrayBag otherBag) {        if (otherBag == null || otherBag.numItems == 0) {            return false;        }                for (int i = 0; i < otherBag.numItems; i++) {            if (! this.contains(otherBag.items[i])) {                return false;            }        }                return true;    }        /**     * grab - returns a reference to a randomly chosen item in this ArrayBag.     */    public Object grab() {        if (this.numItems == 0) {            throw new IllegalStateException("the bag is empty");        }                int whichOne = (int)(Math.random() * this.numItems);        return this.items[whichOne];    }        /**     * toArray - return an array containing the current contents of the bag     */    public Object[] toArray() {        Object[] copy = new Object[this.numItems];                for (int i = 0; i < this.numItems; i++) {            copy[i] = this.items[i];        }                return copy;    }        /**     * toString - converts this ArrayBag into a string that can be printed.     * Overrides the version of this method inherited from the Object class.     */    public String toString() {        String str = "{";                for (int i = 0; i < this.numItems; i++) {            str = str + this.items[i];            if (i != this.numItems - 1) {                str += ", ";            }        }                str = str + "}";        return str;    }        /* Test the ArrayBag implementation. */    public static void main(String[] args) {        // Create a Scanner object for user input.        Scanner scan = new Scanner(System.in);                // Create an ArrayBag named bag1.        System.out.print("size of bag 1: ");        int size = scan.nextInt();        ArrayBag bag1 = new ArrayBag(size);        scan.nextLine();    // consume the rest of the line                // Read in strings, add them to bag1, and print out bag1.        String itemStr;                for (int i = 0; i < size; i++) {            System.out.print("item " + i + ": ");            itemStr = scan.nextLine();            bag1.add(itemStr);        }        System.out.println("bag 1 = " + bag1);        System.out.println();                // Select a random item and print it.        Object item = bag1.grab();        System.out.println("grabbed " + item);        System.out.println();                // Iterate over the objects in bag1, printing them one per        // line.        Object[] items = bag1.toArray();        for (int i = 0; i < items.length; i++) {            System.out.println(items[i]);        }        System.out.println();                // Get an item to remove from bag1, remove it, and reprint the bag.        System.out.print("item to remove: ");        itemStr = scan.nextLine();        if (bag1.contains(itemStr)) {            bag1.remove(itemStr);        }        System.out.println("bag 1 = " + bag1);        System.out.println();         scan.close();    }}