Need help bad!!

[ddmeightball]

I am having problems with an assignment in my advanced java class.

Here it is. I am supposed to use something like an arraylist or linked list to make a dynamically changing program that holds the products for a video company. The problem is the fact that I have never used an arraylist or linked list so I dont know where to start.

You are part of a team of programmers that is developing a point of sale application for a local video store called SCC Pictures and Stuff.  The application needs a class that holds a list of the products offered for sale.  The list of products can vary in number.  Create the ProductList class.  Include a data structure that holds Product objects.  Include the following methods:

add(Product p) – add a product to the list
add(String id, String name, double price) – create a Product and add to the list
size()  - return how many are in the list
remove(int index) – remove a product at position index.
get(int index) – return the Product at position index.
find(String find) – return a Product based on the ID#.

Create a list of Product objects in the constructor of the ProductList class.

Download the Product class from the micros ftp site – it is in the assignments directory.

ProductList class includes:
	Dynamic data structure as an attribute
	Constructor adds Products to the list
	add method s
	size method
	remove method
 	get Method
	find method

Here is the product class were are supposed to use.

public class Product{
	private String code;
	private String name;
	private double price;

	public Product(){
	}

	public Product(String code, String name, double price)
		{
			this.code = code;
			this.name = name;
			this.price = price;
		}

	public void setCode(String c)
		{
			code = c;
		}
		
	public String getCode()
		{ 
			return code;
		}

	public void setName(String d)
		{
			description = d;
		}
		
	public String getName()
		{ 
			return name;
		}

	public void setPrice(double p)
		{
			price = p;
		}
		
	public double getPrice()
		{ 
			return price; 
		}

}

<Moderator added green checkmark to the first post>

[ddmeightball]

OK, before anyone says, " WE WONT DO YOUR ASSIGNMENT!!!!" i dont expect you to. I just want some help with the code that i am writing. Here it is. Any help would be appreciated.

package assignment;
import java.util.*;

public class ProductList extends Product{
	public ProductList() {

	}

	public Object add(Product p)
		{//add a product to the list
			products.add(p);//put product object in array list
		}

	public String add(String id, String name, double price)
		{//create a Product and add it to the list
			for(int i = 0 ; i<products.size(); i++)
				{
					Product prod(i) = new Product(id,name,price);
					products.add(prod(i));
				}
		}

	public int size()
		{//return how many are in the list
			int size;
			size = products.size();
			return size;
		}
	
	public int get(int index)
		{//return the Product at position index
			products.get(index);
			return index;
		}
		
	public int remove(int index)
		{//remove the Product at position index
			products.remove(index);
			return index;
		}
	
	public String find(String find)
		{//return a Product based on the ID#
		
			return find;
		}
	
	public static void main(String[] args) 
		{
			ArrayList products = new ArrayList();

			Product prod1 = new Product("5248","trumpet" , 50);
			Product prod2 = new Product("5420","Saxaphone" , 100);


			for(int i=0; i <products.size(); i++)
				{
					Product p = (Product)products.get(i);
					System.out.println(p.toString());
				}
			
			Iterator it = products.iterator();
			
			while(it.hasNext())
				{
					Product p = (Product)it.next();
					System.out.println(p.toString());
				}
		}
}

[CornedBee]

Well, what exactly is your problem?

There's documentation for ArrayList. I'm also sure that if you search for that term on the forum, you can find some usage examples.

[ddmeightball]

sorry, it didnt post the error part of that message Corned Bee

I get the message "Cannot resolve symbol class Product"

[System_Error]

Is the product class in the same directory as your other class? And did you compile it? I can't remember if you would have to compile it or not..

[System_Error]

public void setName(String d)
		{
			description = d;
		}

You have this in the product class, but I don't see any variable named description.

[ddmeightball]

Is the product class in the same directory as your other class? And did you compile it? I can't remember if you would have to compile it or not..

yeah, Im using a program called JCreator Pro and it automatically makes it into its own directory and makes a project of it.

I tried compiling and got the Cannot Resolve System Symbol Product error

[Dillinger4]

I see a package directive at the top of the ProductList class but not the Product class.

[CornedBee]

Yeah, pretty sure it's a directory issue.
It should look like this:

source_root\
  -> Product.java
  -> assignment\
    -> ProductList.java

[ddmeightball]

Ok, i got around the "Cannot resolve symbol class Product" error by removing the package and just putting them in the same directory.

Now I am getting the error "non-static variable products cannot be referenced from a static context."

here is an update on my code. I have placed comments with the // near the bottom where the compiler has the problem.

/**
 * Title:        Assign 2
 * @author       Matthew Davis
 * School		 SECC
 * Class		 Advanced Java
 */

import java.util.*;

public class ProductList extends Product{
	ArrayList products = new ArrayList();

	public ProductList() {
			Product prod1 = new Product("5248","trumpet" , 50);
			Product prod2 = new Product("5420","Saxaphone" , 100);

	}

	public void add(Product p)
		{//add a product to the list
			products.add(p);//put product object in array list
		}

	public void add(String id, String name, double price)
		{//create a Product and add it to the list
			for(int i = 0 ; i<products.size(); i++)
				{
					Product prod1 = new Product(id,name,price);
					products.add(prod1);
				}
		}

	public int size()
		{//return how many are in the list
			return products.size();
		}
	
	public Object get(int index)
		{//return the Product at position index
			return products.get(index);
		}
		
	public void remove(int index)
		{//remove the Product at position index
			products.remove(index);
		}
	
	public Object find(String find)
		{//return a Product based on the ID#
			Iterator it = products.iterator();
			
			while(it.hasNext())
				{
				
					Product q = (Product)it.next();//returns an object
					if (q.getCode().equals(find))
					{
						return q;
					}
				}
			return null;
		}
		
	public static void main(String[] args) 
		{
			for(int i=0; i < products.size(); i++){//non-static variable products cannot be referenced from a static
													//context
				Product p = (Product)products.get(i);//non-static variable products cannot be referenced from a static
													//context
				System.out.println(p.toString());
			}
			
			Iterator it = products.iterator();//non-static variable products cannot be referenced from a static
													//context
			
			while(it.hasNext()){
				Product p = (Product)it.next();
				System.out.println(p.toString());
			}
			
		}
}

[ddmeightball]

An update

I thought it might have something to do with my arraylist.

So i copied and pasted it from the top of my class down into the main method, now I dont get the error, but it also isnt printing anything because there is technically nothing in the arrayList since it doesnt do anything with the rest of the program. Any ideas?

[CornedBee]

You can't directly access the various variables from main(). You have to create an object of your class first.

[ddmeightball]

OK, i figured out what i was doing wrong. I didnt have an it() method. Now it works. Thanks

public Iterator it()
    {
        return products.iterator();
    }

here is the finished code for both my methods.

first Product.java

/**
 * Title:        Assign 2
 * @author       Matthew Davis
 * School		 SECC
 * Class		 Advanced Java
 */
public class Product{
	private String code;
	private String name;
	private double price;

	public Product(){
	}

	public Product(String code, String name, double price)
		{
			this.code = code;
			this.name = name;
			this.price = price;
		}

	public void setCode(String c)
		{
			code = c;
		}
		
	public String getCode()
		{ 
			return code;
		}

	public void setName(String n)
		{
			name = n;
		}
		
	public String getName()
		{ 
			return name;
		}

	public void setPrice(double p)
		{
			price = p;
		}
		
	public double getPrice()
		{ 
			return price; 
		}
		
	public String toString()
		{
			return code + "\t" + name + "\t" + price + "\t";
			//return code + " " + name + " " + price;
		}


}

and now my productList.java

/**
 * Title:        Assign 2
 * @author       Matthew Davis
 * School		 SECC
 * Class		 Advanced Java
 */

import java.util.*;

public class ProductList extends Product{
	ArrayList products = new ArrayList();

	public ProductList() {

	}

	public void add(Product p)
		{//add a product to the list
			products.add(p);
			
		/*String key = ((Product)p).getCode();
			if(find(key) == null)
				{
					products.add(p);
				}*/
		}

	public void add(String id, String name, double price)
		{//create a Product and add it to the list
			for(int i = 0 ; i<products.size(); i++)
				{
					Product prod1 = new Product(id,name,price);
					products.add(prod1);
				}
		}

	public int size()
		{//return how many are in the list
			return products.size();
		}
	
	public Object get(int index)
		{//return the Product at position index
			return products.get(index);
		}
		
	public void remove(int index)
		{//remove the Product at position index
			products.remove(index);
		}
	
	public Object find(String find)
		{//return a Product based on the ID#
			Iterator it = products.iterator();
			
			while(it.hasNext())
				{				
					Product q = (Product)it.next();
					if (q.getCode().equals(find))
					{
						return q;
					}
				}
			return null;
		}
		
public Iterator it()
    {
        return products.iterator();
    }

		
	public static void main(String[] args) 
		{
			ProductList pr = new ProductList();
            
            Product prod1 = new Product("5248","trumpet" , 50);
            Product prod2 = new Product("5420","Saxaphone" , 100);
            
            pr.add(prod1);
            pr.add(prod2);
            
            Iterator it = pr.it();
            
            while (it.hasNext())            
            {
                Product p = (Product)it.next();
                System.out.println(p.toString());
            }
   
			
		}
	}