将对象与集合中的唯一标识符进行排序和关联

Question

I'm working my through an assignment and got stuck on step 5, would appreciate any help.

1. Carefully study the class structure in Products.java.
2. Design a generic container called GenericOrder that acts as a collection of an arbitrary number of objects in Products.java. Design a mechanism that gives each instance of the container a unique identifier. Implement as many methods as necessary. You must use Java generics features.
3. Design and implement a subclass of GenericOrder called ComputerOrder that takes an arbitrary number of different classes of ComputerPart objects, Peripheral objects, and Service objects. Implement as many methods as necessary.
4. Design and implement a subclass of GenericOrder called PartyTrayOrder that takes an arbitrary number of different classes of Cheese objects, Fruit objects, and Service objects. Implement as many methods as necessary.
5. Design and implement a class called OrderProcessor. You must implement at least the following methods:
   • accept; // this method accepts a GenericOrder or any of its subclass objects and stores it in any internal collection of OrderProcessor.
   • process; // this method sorts all accepted orders in the internal collection of GenericOrder into collections of ComputerPart, Peripheral, Cheese, Fruit, and Service. You must associate each object with the unique identifier. You may refer to the TwoTuple.java example in the text book.
   • dispatchXXX; // this method simulates the dispatch of the sorted collections. For example, the method dispatchComputerParts() should produce this output:
     • Motherboard name=Asus, price=$37.5, order number=123456
     • Motherboard – name=Asus, price=$37.5, order number=987654
     • RAM – name=Kingston, size=512, price=$25.0, order number=123456
6. Create a client class to test OrderProcessor. You will need to create a datagenerator for testing purpose. It is not mandatory but you may use a variation of Data Generator in TIJ pages 637 to 638.

Here is what I have for Q5

public abstract class OrderProcessor<T> {
    private ArrayList<T> dataCollection = new ArrayList<T>();

    public void accept(T item){
        dataCollection.add(item);
    }

    public void process(){
        Collections.sort(dataCollection);
    }

    public List getDataCollection(){
        return dataCollection;
    }
} 

In its current state Collections.sort(dataCollection); doesn't compile because it does not accept T and if I change the ArrayList to String any function used from other subclasses won't work because they all T . Any help would be greatly appreciated.

thanks in advance.

Answer 1

EDIT: Since you want to partition your orders and not sort, you can use something like this:

dataCollection.stream().collect(
  Collectors.groupingBy(order -> order.getIdentifier())
)

Here, this groups them by their identifiers and puts them into a Map . The order.getIdentifier() part is just a placeholder for whatever you want to use to divide them up. The return type will be Map<TypeOfIdentifier, T> .

For this to work, though, your T has to be of some specific type ( T extends Product perhaps?) so you can get the identifier. Since I don't know the code for differentiating between different products, I can't put the exact code here.

The Javadoc for Collectors

---

This is why Collections.sort wasn't working for you, but you don't need Collections.sort anyways.

T must extend the Comparable interface, because obviously you can't sort objects of just any type. The Comparable interface has a compareTo method that lets you sort.

An alternative would be to write a custom Comparator that defines a single method: compare , which would take 2 objects of type T and return an int representing the order (in most cases it's basically the first argument minus the second argument). For this, you would need to use Collections.sort(dataCollection, customComparator) .

You can define your comparator with a lambda expression, but I can't help you beyond that because I have no idea how you want to sort your objects.