Question

I am a beginner in programming. I am still learning about threads and more of them. But now I have quite a big idea to write my first program (I mean bigger than simple calculator). I want it to sort files, integrate in one (many copies of one file in different localization - the idea of it is of no importance now).

But I want to create threads, or anything else (what is your advice). I mean. When I start the program, the console starts up, and e.g I have to write "my_programm run" or "my_program stop" or "my_program status" or "my_magic_tricks be_done". I mean how can i create a program working in the background like in threads with real time string control over it. I tried to find out on Google for anything which could be useful for me, but i didn't find it out.

Please give me just a name of libraries or methods, which I can use. I will read out, what it is about and finally I will move forward with it.

If it is a dumbass question. I am really sorry for disapointing the programmer group. But it would be nice to be given of any signpost or clue.

Answer 1

A simple way to do it using the standard library :

import java.util.Scanner;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.ThreadPoolExecutor;

import static java.util.concurrent.TimeUnit.MILLISECONDS;

public class Example {
    private static final int POOL_SIZE = 5;
    private static final ExecutorService WORKERS = new ThreadPoolExecutor(POOL_SIZE, POOL_SIZE, 1, MILLISECONDS, new LinkedBlockingDeque<>());

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (true) {
            System.out.print("> ");
            String cmd = sc.nextLine();
            switch (cmd) {
                case "process":
                    WORKERS.submit(newExpensiveTask());
                    break;

                case "kill":
                    System.exit(0);

                default:
                    System.err.println("Unrecognized command: " + cmd);
            }
        }
    }

    private static Runnable newExpensiveTask() {
        return () -> {
            try {
                Thread.sleep(10000);
                System.out.println("Done processing");
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        };
    }
}

This code lets you run heavy tasks asynchronously while the user terminal remains available and reactive.

Answer 2

I would recommend reading up on specific tutorials, such as the Java Language Tutorial (available as a book - at least, it used to be - as well as on the Java website https://docs.oracle.com/javase/tutorial/essential/concurrency/)

However as others have cautioned, getting into threading is a challenge and requires good knowledge of the language quite apart from the aspects of multithreading and synchronization. I'd be tempted to recommend you read some of the other tutorials - working through IO and so on - first of all.

JAVA real time consol-control the threads

2 个答案: