Help with inheritance....

[CornedBee]

You can, however, let a base reference point to a derived object:
Product pr = new MusicCD(...);

This is how you make the ProductList work. You can have it store a mixture of all Product subclasses.

[ddmeightball]

Here is an update on my code since i havent posted here in a while.

My Product superclass. No compiler errors

package AssignmentTwo;

public abstract class Product{
	protected String code;
	protected String name;
	protected double price;
	protected String playingTime;


	public Product(){
	}

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

	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 void setPlayingTime(String t)
		{
			playingTime = t;
		}
		
	public String getPlayingTime()
		{ 
			return playingTime; 
		}

    public String showInfo()
    	{
			return this.code + "\t" + this.name + "\t" + this.price + "\t" + this.playingTime + "\t" ;
		}
		
//	protected abstract String showInfo();

My ProductList class. I get a compiler error at line 26. Saying the Product class cannot be instantiated. I know this, but how would I create a product then add it to the list if I can instantiate the Product class. I thought about doing it from the subclasses, either MusicCD or MovieDVD. But then I could only do one or the other, not both. I have marked the error in red.

package AssignmentTwo;

import java.util.*;

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

	public ProductList() {

	}

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

	public void add(String id, String name, double price, String playingTime)
		{//create a Product and add it to the list
			for(int i = 0 ; i<products.size(); i++)
				{
					Product prod1 = new Product(id,name,price, playingTime);//Cannot Instantiate Product
					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 MusicCD("111","Highway to Hell",15,"1 Hour", "AC/DC", 11);
            Product prod2 =  new MusicCD("222","Back In Black",15,"3 Hours", "AC/DC", 17);
//            Product prod3 =  new MovieDVD("333","Rocky V",20,"2 Hours", "Stalone",);
            
            pr.add(prod1);
            pr.add(prod2);
//            pr.add(prod3);
            /*
            Iterator it = pr.it();
            
            while (it.hasNext())            
            {
                Product p = (Product)it.next();
                System.out.println(p.showInfo());
            }*/
   
			
		}
 
	    
		}

My MusicCD class. No compiler errors.

package AssignmentTwo;

public class MusicCD extends Product{
	
	private String artist;
	private int numberOfTracks;

	public MusicCD() 
		{
			
			artist="";
			numberOfTracks = 0;
			code= this.getCode();
			name=this.getName();
			price=this.getPrice();
			playingTime=this.getPlayingTime();

		}	
	
	
	public MusicCD(String code, String name, double price, String playingTime, String a, int n) 
		{
			super(code, name, price , playingTime);
			artist=a;
			numberOfTracks = n;
		}	
		
				
	public String getArtist()
		{
			return artist;
		}
	
	public void setArtist(String a)
		{
			artist=a;
		}
		
	public int getNumberOfTracks()
		{
			return numberOfTracks;
		}
	
	public void setNumberOfTracks(int n)
		{
			numberOfTracks = n;
		}

	public String showInfo(){
		return this.getName() + " " + this.getPrice() + " " + 
					this.getPlayingTime()+ artist + " " + numberOfTracks + " " + this.getCode();
	}


}

My MovieDVD class. No compiler errors.

package AssignmentTwo;

public class MovieDVD extends Product{
	
	private String director;
	private int scenes;

	public MovieDVD() 
	{
			director="";
			scenes=0;
			code= this.getCode();
			name=this.getName();
			price=this.getPrice();
			playingTime=this.getPlayingTime();
	}	
	
	
	public MovieDVD(String code, String name, double price, String playingTime, String d, int s)
		{
			super(code, name, price , playingTime);
			director=d;
		}	
		
				
	public String getDirector()
		{
			return director;
		}
	
	public void setDirector(String d)
		{
			director=d;
		}
		
	public int getScenes()
		{
			return scenes;
		}
	
	public void setScenes(int s)
		{
			scenes=s;
		}

		
	public String showInfo(){
		return this.getCode()+" " + this.getName() + " " + this.getPrice() + " " + 
					this.getPlayingTime()+ director + " " + scenes ;
	}
}

And finally my ProdTest class. No compiler errors.

package AssignmentTwo;
import java.util.*;

public class ProdTest {
	  	public static void main(String[] args) 
		{
			ProductList pr = new ProductList();
            
            
            Iterator it = pr.it();
            
            while (it.hasNext())            
            {
                Product p = (Product)it.next();
                System.out.println(p.showInfo());
            }
   
			
		}


}

[ddmeightball]

I wrote a test class to show polymorphism by retrieving Products from the ProductList object and executing the showInfo() method for each. I believe I got that part right, but am not sure. Someone correct me if I am wrong.

I have been working on this on and off all day and I did what CB said. Infact, when you were posting it I had just got done implementing this in my class.

Now, for the last problem(hopefully) for my program. I am supposed to Change the ProductList class to include these objects, the MusicCD and MovieDVD objects, instead of the generic Product objects, if needed. But how would I go about doing that?

Someone on another site suggested this bit of code to add to my ProductList class.

public void add(Product p) {
if (find(p.getCode()) == null)
products.add(p);
}

The problem with this is the getCode method is used to get the code for the product. The way i coded this, is to keep duplicate products from being added to the arraylist. What they suggested is pretty much what I have done here correct?

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

the method that I need to figure out how to change is this add method that creates the object and then adds it to the arraylist. The only thing is though, how would I get it to distinguish between a MusicCD and a MovieDVD???

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