estorebasket.java

E-store CMU SSD7 EXE4答案. 实现要求全部功能 绝对满分

package estore;
import java.util.*;

/**
 * Class <b>EStoreBasket</b> contains
 * the specification of a JaveBean modeling
 * a basket at a E-Store.
 *
 * @author A Jiayi
 * @version 1.0
 */

public class EStoreBasket {

	/**
	* The Book hashtable stores all of the books in the 
	* E-Store basket.  The key is the book isbn, the value 
	* stored is the quantity of that book. Initially, the 
	* Book hashtable has a size of 15 and a load factor of .75.
	*/
	Hashtable Books = new Hashtable( 15, (float) .75 );
	int numBooks=0;
    
	/**
	* Empty constructor.  All JavaBeans must have an empty constructor.
	* The student is not repsonsible for adding any code to this function.
	*/
	public EStoreBasket() {}

	/**
	* Remove an item from the E-Store basket.
	* @param ISBN String input isbn to remove
	* @return void
	*/
	public void removeItem( String ISBN ) {
		Integer Quantity;

		//get the quantity of the book from the hash table.
		Quantity = (Integer) Books.get( ISBN );

		//a null quantity means that no book with this ISBN is in the hashtable
		if (Quantity==null) {
			return;
		}

		/**
		* If there is only one copy of this particular book in the hash table, remove
		* the entry totally from the hash table.
		*/
		if (Quantity.intValue()==1) {
			Books.remove( ISBN );
			numBooks--;
		}
		/**
		* If the quantity of this ISBN is greater than 1, 
		* decrement the quantity and place the
		* new quanity back into the hashtable.
		*/
		else {
			int tempQuant = Quantity.intValue();
			tempQuant--;
			Books.remove( ISBN );
			Books.put( ISBN, new Integer(tempQuant) );
		}
	}
	
	/**
	* Add an item to the E-Store basket.
	* @param ISBN String isbn of item to add
	* @return void
	*/
	public void addItem( String ISBN ) {
		Integer Quantity;
		// Get the quantity for this book in the basket.
		Quantity = (Integer) Books.get( ISBN );
		/**
		* If the quantity is null, then this book is not in the basket, so
		* add it to the hashtable.
		*/
		if (Quantity==null) {
			Quantity = new Integer(1);
			Books.put( ISBN, Quantity );
			numBooks++;
		}
		/**
		* If the book is in the basket, remove the entry
		* from the hash table and place the newly incremented 
		* quantity in back into the basket.
		*/
		else {
			int tempQuant = Quantity.intValue();
			tempQuant++;
			Books.remove( ISBN );
			Books.put( ISBN, new Integer(tempQuant) );
		}
	}

	/**
	* Return the number of distinct books in the basket.
	* @return int
	*/
	public int getnumBooks() {
		return numBooks;
	}

	/**
	* Get the total number of books in the basket for a given ISBN.
	* @param ISBN String isbn of book
	* @return int
	*/
	public int getQuantity( String ISBN ) {
		Integer Quantity;
		Quantity = (Integer) Books.get( ISBN );
		if (Quantity==null) {
			return 0;
		} else {
			return Quantity.intValue();
		}
	}

	/**
	* Return an array of strings which are all of the distinct isbns in the basket.
	* @return String[]
	*/
	public String[] getBooks() {
		String[] returnISBNs = new String[Books.size()];
		int currPos = 0;
		for( Enumeration bookEnumeration = Books.keys(); bookEnumeration.hasMoreElements(); ) {
			returnISBNs[currPos] = (String) bookEnumeration.nextElement();
			currPos++;
	    	}
		return returnISBNs;
	}
}