class Task {
    void executeTask() {
        System.out.println("Task is being executed");
    }
}

class NonNumericTypeException extends Exception {
    NonNumericTypeException(String msg) {
        super(msg);
    }
}

class SumTask<T extends Number> extends Task {
    synchronized T sum(T a, T b) throws NonNumericTypeException {
        if (a == null || b == null) throw new NonNumericTypeException("Non-numeric type");
        return (T) Double.valueOf(a.doubleValue() + b.doubleValue());
    }
}

public class Main {
    public static void main(String[] args) throws NonNumericTypeException {
        SumTask<Double> task = new SumTask<>();
        task.executeTask();
        System.out.println(task.sum(3.0, 4.0));
    }
}