Help please? What should I do here?

Question about the task

Under discussion

Can anyone please provide some pointers?

1. Read online about Socket, ThreadPoolExecutor, RunnableFuture, and Callable.
2. Implement the logic of the SocketTask class's cancel() method.
3. Implement the cancel() method's logic for a local class inside the SocketTask class's newTask method.

Requirements:

Don't change the SocketTask class definition (its fields or method signatures).
The SocketTask class's cancel() method must close the resources used by the class.
The cancel() method for the local class inside the newTask method must close the SocketTask resources and call the parent class's cancel() method.
The parent class's method must be called even if an exception is thrown while closing resources.

package com.codegym.task.task25.task2509; import java.util.concurrent.*; /* It's not as easy as it seems */ public class Solution extends ThreadPoolExecutor { public Solution(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue); } protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { if (callable instanceof CancellableTask) { return ((CancellableTask<T>) callable).newTask(); } else { return super.newTaskFor(callable); } } public static void main(String[] args) { } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

27 April 2021, 14:11

useful

#1 Consider that calling a method on any object that you do not specifically create could result in an Exception being thrown if the Object does not exist. When the case is that you didn't create the object yourself then your default action should ALWAYS be to guard against this Exception. #2 An inner, non static, class (anonymous or not) has access to everything inside an instance of the outer class regardless of the access modifiers because the inner class is an instance directly connected to an instance of the outer class while not being a direct child. Think of it as being conjoined to the outer class. You can not create an instance of an inner class by itself, but need to 1st create an instance of the outer class. So:

//can't create an inner class like this by itself
InnerClass x = new InnerClass();

//to create an inner class you need an instance of the outer class
OuterClass outer = new OuterClass();
InnerClass inner = outer.new InnerClass();

// or you can create an anonymous class in an object method of the outer
// class and the connection is made implicitly
public InnerClass test() {
   return new InnerClass(); //<-- this is an instance of OuterClass.InnerClass
}

It may seem confusing, but you already have seen and used this for 10 levels or more. The interface Iterator is created this way. It needs an object first of a class that is Iterable, and then you can call the .iterator() method on that class. This causes the class to return the Iterator object that is generated internally as an anonymous class, and you can then sequentially access the data stored within in a standard way.

Iterator<type> iterator = HashSet.iterator();
ArrayList.iterator();
TreeSet.iterator();
LinkedList.iterator();
HashMap.entrySet.iterator();
//etc...

Guadalupe Gagnon

Level 37 , Tampa, United States

27 April 2021, 14:13

I say all that because in this task the newTask() method is returning an anonymous innerclass, so it will be conjoined with an instance of the outer class. You can use this to call the correct cancel method, and the super class of that instance will be FutureTask<T>.

Andrei

Level 41

27 April 2021, 16:02

Hi Guada, thanks for the explanation, I understand some parts of your comments. Unfortunately I feel like I have skipped a few months of school with the last few levels because the concepts they are presenting seem to be more and more complicated and less and less detailed. I don't know what is going on but it is becoming quite frustrating because CodeGym, instead of being a guiding resource, starting with level 20 has slowly become 'lazy' in explaining concepts and guiding students. I understand that we have to study ourselves, but to give an exercise and then task the student to "read online about Socket, ThreadPoolExecutor, RunnableFuture, and Callable." is a bit unfair. I feel a couple more lessons could have been included to detail these concepts and present some examples as well. These are 4 concepts which are almost brand new, talking about communication between 2 machines, taking threads out of pools , future (??? I don't even know what this is yet)... I feel like I have to study about 20 hours more on the side just to understand how these 4 concepts work.

Guadalupe Gagnon

Level 37 , Tampa, United States

27 April 2021, 16:25

I think you are complicating the task too much. You're cancel method is only missing one thing (the check for null values). For the FutureTask.cancel(), you should be able to get how to implement it by just looking that up "FutureTask.cancel": Here is a link i found that applies quite well with this task: Cancelling Tasks Approach #2 - skip to the line that says "Now we need to define our task as follows:". The code directly following mirrors this task.

Andrei

Level 41

28 April 2021, 05:56

Thanks.