import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.List;
import java.util.ArrayList;
import java.util.concurrent.*;

public class Calka_callable implements Callable<Double>
{
    private double pocz;
    private double kon;
    private double dx;
    private double xp;
    private double xk;
    private int N;
    public static final int watki = 1;

    public Calka_callable(double xp, double xk, double dx)
    {
        this.xp = xp;
        this.xk = xk;
        this.pocz = xp;
        this.kon = xk;
        this.N = (int) Math.ceil((xk-xp)/dx);
        this.dx = (xk-xp)/N;
        System.out.println("Creating an instance of Calka_callable");
        System.out.println("xp = " + xp + ", xk = " + xk + ", N = " + N);
        System.out.println("dx requested = " + dx + ", dx final = " + this.dx);
    }

    private double getFunction(double x)
    {
        return Math.sin(x);
    }

    public double compute()
    {
        double calka = 0;
        int i;
        for(i=0; i<N; i++)
        {
            double x1 = xp+i*dx;
            double x2 = x1+dx;
            calka += ((getFunction(x1) + getFunction(x2))/2.)*dx;
        }
        return calka;
    }

    @Override
    public Double call() throws Exception
    {
        double calka = compute();
        System.out.println("Calka czastkowa: w przedziale : ["+pocz+"; "+kon+"] = " + calka);
        return calka;
    }

    public static void main(String[] args)
    {
        ExecutorService executor = Executors.newFixedThreadPool(watki);
        List<Future<Double>> list = new ArrayList<>();

        double suma = 0.0, poczatek = 0.0, koniec = 5, l_zadan = 16;
        double start, stop;

        for(int i = 0; i < l_zadan; i++)
        {
            double x = ((koniec - poczatek) / l_zadan);
            start = i * x;
            stop = start + x;
            Callable<Double> callable = new Calka_callable(start, stop,0.0001);
            Future<Double> future = executor.submit(callable);
            list.add(future);
        }
        for(Future<Double> el:list)
        {
            try
            {
                suma = suma + el.get();
            }
            catch(InterruptedException | ExecutionException e)
            {
                e.printStackTrace();
            }

        }

        //executorService.shutdown();
        //while(!executorService.isTerminated()){
        //
        //}
        System.out.println("\nCalka = "+suma);
        executor.shutdown();
    }
}