Threads.java

import java.security.SecureRandom;
import java.time.LocalDateTime;
import java.util.Optional;
import java.util.concurrent.TimeUnit;

public class BusyTask {

    private final int time;
    private final String id;
    private LocalDateTime start = null;
    private LocalDateTime end = null;

    private BusyTask(int start, int end) {
        this.time = new SecureRandom().nextInt(end) + start;
        this.id = String.format("BW%05d", time);
    }

    public static BusyTask newBlueInstance() {
        return new BusyTask(3, 12);
    }

    public static BusyTask newRedInstance() {
        return new BusyTask(12, 24);
    }

    public int execute() {
        try {
            start = LocalDateTime.now();
            //some I/O operation
            TimeUnit.SECONDS.sleep(time / 2);
            TimeUnit.SECONDS.sleep(time / 2);
            end = LocalDateTime.now();
        } catch (InterruptedException ignored) {
        }
        return time;
    }

    public Optional<LocalDateTime> start() {
        return Optional.ofNullable(start);
    }

    public Optional<LocalDateTime> end() {
        return Optional.ofNullable(end);
    }

    public int getTime() {
        return time;
    }

    public String getId() {
        return id;
    }
}


public class UseBusyTask{
    public static void main(String)
    {
        final BusyTask task = BusyTask.newBlueInstance();
        task.id();
    }
}