a subclass taking unlimited objects of only a few classes

[Kiley smith]

Hi everyone,

I have:
First class:1) Product
Subclasses of Parent: 1.1) Cheese - 1.2) ComputerParts - 1.3) Service - 1.4) Fruit
SubSubclasses of Computer parts: 1.2.1) Ram - 1.2.2) Peripheral
Sub Sub Subclasses of Peripheral: 1.2.2.1) Printer - 1.2.2.2) Monitor


I need to code a subclass of a class called GenericOrder and call it ComputerOrder which will take an arbitrary number of only ComputerParts Objects, Peripheral Objects and Service Objects.

BTW my GenericsOrder class is:

class GenericOrder<T> {

ArrayList<T> list1 = new ArrayList<T>();
int ID = System.identityHashCode(list1);
public void add(T item){
list1.add(item);
}
public void remove(T item) {
list1.remove(item);
}
public T get (int index){
return list1.get(index);
}
public int GetID(){
return ID;
}
}

I'm very stuck, I'm afraid this is as far as I've gotten:

class ComputerOrder<C extends ComputerPart,P extends Peripheral,S extends Service, T> extends GenericOrder<T>{
	public C varC;
	public P varP;
	public S varS;
	
	public ComputerOrder(C aVarC, P aVarP, S aVarS){
		varC = aVarC;
		varP = aVarP;
		varS = aVarS;
	}
	ArrayList<T> list1 = new ArrayList<T>(); ***
	public void add(T item){
		list1.add(item);
	}
}
	
	
}

*** but this is incorrect: i need to be able to take an arbitrary number of different classes of ComputerPart objects, Peripheral objects and Service objects.

Many thanks,

[Andrey Kozhanov]

Create some declarative interface (for example, call it IComputer) and implement it in classes you want to add to a list. Then your list will be declared like this: ArrayList<IComputer>.

[Kiley smith]

This sounds promising but I don't really know how to do it. I know how to create just an interface but not one in a class.

[Campbell Ritchie]

There is a lot of controversy about tagging interfaces, but this is how you can do it

public interface IComputer
{
}

public class Foo extends Bar implements IComputer
{
 ...
}

[Campbell Ritchie]

You can probably also do it with an annotation, but I am not sure how. Anybody else?

[Kiley smith]

Hi everyone,
Thank you for sticking with me. I have posted the class structure here: www.netmatrix.com/classes.jpg

This is where I am at:

class ComputerOrder<T extends IComputerOrder> extends GenericOrder<T>{
	public void add(T item){
		super.add(item);
	}
}

interface IComputerOrder {
	public void add(ComputerPart obj);
	public void add(Peripheral obj);
	public void add(Service obj);
}

This doesn't seen quite right to me. I understand interfaces cannot have any logic (definitions in them) so I need somehow check that only ComputerPart, Peripheral or Service objects are permitted. Did I create the interface correctly or is this what it is supposed to be:

interface IComputerOrder {
	public void add(Object obj);
	
}

and do error checking in ComputerOrder?

[Darryl Burke]

abstract class Product {
}

class Cheese extends Product {
}

interface ComputerPart {
}

class Service extends Product implements ComputerPart {
}

class Ram implements ComputerPart {
}

abstract class Peripherals implements ComputerPart {
}

class Monitor extends Peripherals {
}

class Printer extends Peripherals {
}

class Order<T> {

  public void add(T t) {
  }
}

class ComputerOrder<T extends ComputerPart> extends Order<T> {

  public static void main(String[] args) {
    ComputerOrder<ComputerPart> order = new ComputerOrder<ComputerPart>();
    order.add(new Printer());
    order.add(new Monitor());
    order.add(new Ram());
    order.add(new Service());

    // order.add(new Cheese()); // -- doesn't compile
  }
}

final edit: Removed irrelevant stuff after modifying the code

[Mike Simmons]

So I guess we're done with this other thread?

http://www.coderanch.com/t/543458/java/java/Generics-tuples-panic

[Kiley smith]

Hi Darryl and Mike,

Darryl's solution works, thank you. Could some help me understand why my version of this does not work:

class ComputerOrder<T extends IComputerOrder> extends GenericOrder<T>{
	public void add(T item){
		if (item instanceof ComputerPart)
			super.add(item);
		else if (item instanceof Peripheral)
			super.add(item);
		else if (item instanceof Service)
			super.add(item);
		else
			System.out.println("cannot add this type of item to the list");
	}
}

interface IComputerOrder {

}

public class ProductMain {
	public static void main(String[] args) {
		
		ComputerPart aComputerPart = new ComputerPart(1);
	
		
		List<IComputerOrder> myComputerOrder = new ArrayList<IComputerOrder>();
		myComputerOrder.add(new ComputerPart(1));
}}

My line "myComputerOrder.add(new ComputerOrder(1));" is wanting an IComputerOrder object. Can someone explain this to me? I really want to understand this. Thank you.

[Kiley smith]

Hi Mike

Yes, this one can be closed or deleted as it's live over here. Thanks

http://www.coderanch.com/t/543458/java/java/Generics-tuples-panic

[Kamal Tripathi]

Kiley smith wrote:Hi Darryl and Mike,

Darryl's solution works, thank you. Could some help me understand why my version of this does not work:

class ComputerOrder<T extends IComputerOrder> extends GenericOrder<T>{
	public void add(T item){
		if (item instanceof ComputerPart)
			super.add(item);
		else if (item instanceof Peripheral)
			super.add(item);
		else if (item instanceof Service)
			super.add(item);
		else
			System.out.println("cannot add this type of item to the list");
	}
}

interface IComputerOrder {

}

public class ProductMain {
	public static void main(String[] args) {
		
		ComputerPart aComputerPart = new ComputerPart(1);
	
		
		List<IComputerOrder> myComputerOrder = new ArrayList<IComputerOrder>();
		myComputerOrder.add(new ComputerPart(1));
}}

My line "myComputerOrder.add(new ComputerOrder(1));" is wanting an IComputerOrder object. Can someone explain this to me? I really want to understand this. Thank you.

Darryl's solution modifies ComputerPart as an interface (rather than a concrete object as the problem suggests). Guessing from what you are trying to implement (after inferring from other answers), your problem may be around the point where you declare interface (IComputerOrder) and how ComputerPart is defined as concrete class. My guess is that your ComputerPart concrete class doesn't implement IComputerOrder interface.

Can you post the code for IComputerOrder and ComputerPart. I am just guessing so I may be wrong.