CODEWITHSUNDEEP
javamultithreadinggenerics
Alexander Ulyanov
Alexander Ulyanov

Reputation: 33

Java Generic Class in use

A lot of search coudnt help me with my problem. While refactoring a lot of code, which realize Producer-Consumer pattern, i get a problem with a simple composition.

By the end of refactoring we have a very simple structure

1) A class Spooler, that shedules Consumer threads.

2) An abstract class AbstractConsumer, that contains some real methods and variables and one abstract method run();

3) Subclasses - real Consumers, that extend AbstractConsumer and override run() method. 

class Spooler {

        private int spoolSize = 100;
        private Consumer[] spool = null;
        //private ArrayList<? extends Consumer> spool = null;
        //...

        public Spooler() {
            init();
        }

        public final void init() {
            if (spool == null) {
                spool = new ArrayList<Consumer>();
                for (int i = 0; i < spool.size(); i++) {
                    spool.add(new Consumer(null, null));
                    spool[i] = new Consumer();
                    spool[i].start();
                }

            }
        }
    }

    public abstract class AbstractConsumer extends Thread {
        //some NOT ABSTRACT variables and methods

        @Override
        public abstract void run();

    }

    class XmlConsumer extends Consumer {

        @Override
        public void run() {
            //consume current task 
        }
    }

So, what i want. When i need some multithreading dataprocessing, i realize current Consumer, override run() method of abstract superclass. Realize new Spooler, which constructor have to get the currentConsumer. And then all it have to work, i think.

I don't know how to add AbstractConsumer into Spoolers ArrayList without implementation its abstract methods. Like that 

for (int i = 0; i < spool.size(); i++) {
            spool.add(new AbstractConsumer() {

                @Override
                public void run() {
                    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
                }
            })

}

I think, its need to use Java Generics Classes here, i tried hard, but all fails. Please tell me how can i solve my problem. Thank you =)

Upvotes: 2

Views: 95

Answers (1)

seneque
seneque

Reputation: 279

if you want your spooler to be generic, you should compose it with a factory that you inject in the constructor of the spooler

interface ConsummerFactory {
  public AbstractConsummer create();
}

so in the init method of your spooler, you invoke the create method of the factory

then if you want a spooler of XmlConsumer you just need to implement a ConsummerFactory whose create method create a XmlConsummer and give it as argument of the constructor of your spooler

Upvotes: 1

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