Hashtable

[sumit sharmast]

Dear All,

I tried to use Hastable in Cart.Java class insted of given arraylist but not able to do it. I tried a lot but not successful. How can I do it, please guide me.

Regards,

Sumit.

import java.text.NumberFormat;
import java.io.Serializable;
import java.text.*;
import java.util.*;
import java.io.Serializable;

public class LineItem implements Serializable
{
	private String description;
    private double price;
    private int count;
    private int quantity;
    private int totalQuantity;
	private String code;
    
	public String getCode() {
		return code;
	}
	public void setCode(String code) {
		this.code = code;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	public int getCount() {
		return count;
	}
	public void setCount(int count) {
		this.count = count;
	}
	public int getQuantity() {
		return quantity;
	}
	public void setQuantity(int quantity) {
		this.quantity = quantity;
	}
	public int getTotalQuantity() {
		return totalQuantity;
	}
	public void setTotalQuantity(int totalQuantity) {
		this.totalQuantity = totalQuantity;
	}
	public double getTotal()
    { 
        double total = price * quantity;
        return total;
    }}

-------------------------------------------------------------------------------------------------------------------------------------------
Below is the arraylist code of this class
--------------------------------------------------------------------------------------------------------------------------------------------

import java.util.*;
import java.io.Serializable;


public class Cart implements Serializable
{
   
	private ArrayList<LineItem> items;
	//private Hashtable<String,LineItem>items;
    
    public Cart()
    {
        items = new ArrayList<LineItem>();
    //	items = new Hashtable<String,LineItem>();
    }
 
    public void setItems(ArrayList<LineItem> lineItems)
    {
        items = lineItems;
    }

    public ArrayList<LineItem> getItems()
    { 
        return items; 
    }
    
    public int getCount()
    { 
        return items.size();
    }
    
    public void addItem(LineItem h)
    {
        
    	for (int i = 0; i<items.size(); i++)
        {
           LineItem lineItem = items.get(i);
           
   if (lineItem.getCode().equals(h.getCode()))
            {
	  
	  lineItem.setQuantity(h.getQuantity());
                return;
                
            }
        }
      items.add(h);
    }
    
  
    
    public void removeItem(LineItem j)
    {
       
        for (int i = 0; i><items.size(); i++)
        {
            LineItem lineItem = items.get(i);
            if (lineItem.getCode().equals(j.getCode()))
        
            {
                items.remove(i);
                return;
            }
        }
    }
}

[Campbell Ritchie]

Don’t use Hashtable; use HashMap instead.

Why are you trying to substitute a Map for a List? The two are different.

I tried to use Hastable in Cart.Java class insted of given arraylist . . .

That is rather like saying, “I tried using a screwdriver instead of a pair of scissors.” Maps and Lists are as different as scissors and screwdrivers, or chalk and cheese. If you need a List, you need a List. Go through the Java Tutorials, and look particularly at the sections about “the Map interface” and “the Map interface”, which should explain how Maps differ from Lists. Only when you understand how they differ will you know which to use. If there is anything you don’t understand, be sure to ask again.

[Winston Gutkowski]

sumit sharmast wrote:I tried to use Hastable in Cart.Java class insted of given arraylist but not able to do it. I tried a lot but not successful. How can I do it, please guide me.

Well, a few things:

1. Your LineItem class isn't very normalized. Specifically:

It contains a totalQuantity field, which is redundant - it's either derived data (ie, price * quantity), or it properly belongs in your Cart class.

It doesn't appear to reference an Item, which is where I would have my price, description and code fields. That doesn't mean that it's not also a good idea to have a price in your LineItem class, but I think I'd call it something like 'salePrice': The one in an Item class might be the MRRP, and the one in the LineItem class the "actual selling price", which would include any discounts or promos.

2. I wouldn't supply setters for every field - or at least I certainly wouldn't make them all public - unless it's required because it's some type of Bean.

3. If you're going to use a HashMap for the LineItems in your Cart, I'd suggest a LinkedHashMap, because they're likely to need a predictable order. But to be honest, an ArrayList seems fine to me, unless you're expecting thousands of LineItems to a Cart.

HIH

Winston

[Seetharaman Venkatasamy]

welcome to JavaRanch sumit sharmast

[sumit sharmast]

Thank you everyone for the suggestions.

[sumit sharmast]

Dear All,

I tried to change from arraylist to hashtable. i changed because I want to see how the same thing is possible with hastable. I am a beginner and I am learning how to do same thing using different collections.

I am getting the following error in the SERVLET CODE. Please help.

ERROR MESSAGE:

HTTP Status 500 -

--------------------------------------------------------------------------------

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception


root cause

java.lang.Error: Unresolved compilation problems:
The method addItem(String, LineItem) in the type Cart is not applicable for the arguments (LineItem)
The method removeItem(String, LineItem) in the type Cart is not applicable for the arguments (LineItem)

music.cart.DisplayCartServlet.doPost(DisplayCartServlet.java:87)
music.cart.DisplayCartServlet.doGet(DisplayCartServlet.java:114)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


note The full stack trace of the root cause is available in the Apache Tomcat/6.0.20 logs.

Apache Tomcat/6.0.20
--------------------------------------------------------------------------------
LineItem.java Code

import java.text.NumberFormat;
import java.io.Serializable;
import java.text.*;
import java.util.*;
import java.io.Serializable;

public class LineItem implements Serializable
{
	private String description;
    private double price;
    private int count;
    private int quantity;
    private int totalQuantity;
	private String code;
    
	public String getCode() {
		return code;
	}
	public void setCode(String code) {
		this.code = code;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	public int getCount() {
		return count;
	}
	public void setCount(int count) {
		this.count = count;
	}
	public int getQuantity() {
		return quantity;
	}
	public void setQuantity(int quantity) {
		this.quantity = quantity;
	}
	public int getTotalQuantity() {
		return totalQuantity;
	}
	public void setTotalQuantity(int totalQuantity) {
		this.totalQuantity = totalQuantity;
	}
	public double getTotal()
    { 
        double total = price * quantity;
        return total;
    }
	
	 public String getPriceCurrencyFormat()
	    {
	       

	NumberFormat nf = NumberFormat.getCurrencyInstance(Locale.ENGLISH);

	String formattedValue = nf.format(price);

	return(formattedValue);

	    }
	
	 public String getImageURL()
	    {
	        String imageURL = "/booksShop/images/" + code + ".jpg";
	        return imageURL;
	    }}

Cart.Java Code

import java.util.*;
import java.io.Serializable;


public class Cart implements Serializable
{
	   
		private Hashtable<String,LineItem>items;
	    
	    public Cart()
	    {
	    
	    items = new Hashtable<String,LineItem>();
	    }
	 
	   
	    public void setItems(Hashtable<String,LineItem> LineItems)
	    {
	    	items=LineItems;
	    	
	    }

	 
	    public Hashtable<String,LineItem> getItems()
	    {
	    	return items;
	    	
	    }
	    public int getCount()
	    { 
	        return items.size();
	    }
    
    public void addItem(String id,LineItem h)
    {
        
    	for (int i = 0; i<items.size(); i++)
        {
           LineItem lineItem = items.get(i);
           
   if (lineItem.getCode().equals(h.getCode()))
            {
	   
	  lineItem.setQuantity(h.getQuantity());
                return;
                
            }
        }
    
    	items.put(id, h);
    }
    
 
    
    public void removeItem(String id,LineItem j)
    {
        
        for (int i = 0; i><items.size(); i++)
        {
         
        	if(items.containsKey(id))
        		
        		items.remove(items);
        	
        	
        	
        }
    }
}

---------------------------------------------------------------------

SERVLET CODE:

import java.io.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Hashtable;

import javax.servlet.*;
import javax.servlet.http.*;

import music.business.*;
import music.data.*;

public class DisplayCartServlet extends HttpServlet
{
    public void doPost(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException, ServletException
    {
        String x = request.getParameter("quantity");
        String y = request.getParameter("productCode");
        String z = request.getParameter("removeButton");
        String ub = request.getParameter("updateButton");
        
 HttpSession session = request.getSession();
        
Cart k = (Cart) session.getAttribute("cart"); 



if (k == null)
{
k = new Cart();
session.setAttribute("cart", k);
}

        
       int quantity;
       try
         {
          quantity = Integer.parseInt(x);
          
        }
        catch(NumberFormatException nfe)
        {
          quantity = 1;
        }
       
        Hashtable><String,LineItem>items=k.getItems();
          for (int i = 0; i<items.size(); i++)
        {
          LineItem v = items.get(i);
          if(v.getCode().equals(y) && ub==null && quantity>0)
          	quantity = v.getQuantity()+ 1;
         
          
          
         }
    


       
        if (z != null)
        {

        	quantity = 0;
        }

       
        LineItem  d = DAO.selectProduct(y);
      
        session.setAttribute("product", d);

        
       
        {
            LineItem t = new LineItem();
         t.setCode(d.getCode());
         t.setDescription(d.getDescription());
            t.setPrice(d.getPrice());
            
            t.setQuantity(quantity);
            if (quantity > 0)
                k.addItem(t); //Error is here,What will be the correct argument
                              // inside the addItem method, in place of addItem(t) ??? 
            
            else if (quantity == 0)
                k.removeItem(t);//Error is here,What will be the correct argument
                                // inside the addItem method, in place of addItem(t) ??? 
        }
        session.setAttribute("cart", k);
        
        
        String url = "";
        if (k.getItems().size() <= 0)
        {
            url = "/cart/quick_order.jsp";
        }
        else
        {
            url = "/cart/cart.jsp";
        }

        RequestDispatcher dispatcher =
                getServletContext().getRequestDispatcher(url);
        dispatcher.forward(request, response);
    }
    
    public void doGet(HttpServletRequest request,
            HttpServletResponse response)
            throws IOException, ServletException
    {
        doPost(request, response);
    }
}

-----------------------------------------------------------------------------------


JDBC CODE:

public static ArrayList< LineItem > selectJavaProducts()
	    {
	        ConnectionPool pool = ConnectionPool.getInstance();
	        Connection connection = pool.getConnection();
	        PreparedStatement ps = null;
	        ResultSet rs = null;
	       
	        
	        String query = "SELECT * FROM Product where category='java'";
	        try
	        {
	            ps = connection.prepareStatement(query);
	            rs = ps.executeQuery();
	            ArrayList<LineItem> products = new ArrayList<LineItem>();
	            while (rs.next())
	            {
	            	 LineItem  p = new  LineItem ();
	             
	                
	                p.setCode(rs.getString("ProductCode"));
	                p.setDescription(rs.getString("ProductDescription"));
	                p.setPrice(rs.getDouble("ProductPrice"));
	               
	                products.add(p);
	            }
	           
	             
	            return products;
	        }
	        catch(SQLException e)
	        {
	            e.printStackTrace();
	            return null;
	        }
	        finally
	        {
	        	try
	            {
	                if (rs != null)
	                    rs.close();
	            } 
	        	catch(SQLException e)
	            {
	                e.printStackTrace();
	            }
	        	try
	            {
	                if (ps != null)
	                    ps.close();
	            } 
	        	catch(SQLException e)
	            {
	                e.printStackTrace();
	            }
	            pool.freeConnection(connection);
	        }
	    }

[Campbell Ritchie]

If you have an unresolved compilation problem, you should go back to Eclipse and over your mouse on the little red mark there. It will give an explanation of the problem and suggest some possible solutions.
You should never have tried to run that code; Eclipse will have give you a warning that there are errors, and you ought to have corrected them then.

[sumit sharmast]

Campbell Ritchie wrote:If you have an unresolved compilation problem, you should go back to Eclipse and over your mouse on the little red mark there. It will give an explanation of the problem and suggest some possible solutions.
You should never have tried to run that code; Eclipse will have give you a warning that there are errors, and you ought to have corrected them then.

What will be the correct argument in the Servlet code inside the addItem method, in place of addItem(t) ???

[Winston Gutkowski]

sumit sharmast wrote:Dear All...

Sumit. Please don't put such long lines in your code blocks. I've broken them up this time, but please re-read the UseCodeTags page. Thoroughly.

Thanks

Winston