import java.util.Random;

public class MonteCarloMultiThread {
    public static void main(String[] args) {
        calcPI(1,10_000_000L);
    }

    static void calcPI(int nThreads, long nTrials) {
        MonteCarloPICalculator[] calculators = new MonteCarloPICalculator[nThreads];
        Thread[]                 ths         = new Thread[nThreads];

        for(int i=0; i<nThreads; i++ ) {
            final MonteCarloPICalculator calculator = new MonteCarloPICalculator("Thread "+ i , nTrials/nThreads);
            calculators[i] = calculator;

            ths[i] = new Thread(){
                public void run() {
                    calculator.calcPI();;
                }
            };
        }

        long start = System.currentTimeMillis();

        for(int i=0; i<nThreads; i++) {
            ths[i].start();
        }

        for(int i=0; i<nThreads; i++) {
            try {
                ths[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        long   time  = System.currentTimeMillis() - start;
        long   count = 0;

        for(int i=0; i<nThreads; i++) {
            count += calculators[i].getCount();
            calculators[i].printResult();
        }

        double result = count / (double)nTrials * 4.0;

        System.out.println("====================");
        System.out.println("All");
        System.out.println("nThreads  : "     + nThreads );
        System.out.println("nTrials   : "     + nTrials );
        System.out.println("count     : "     + count );
        System.out.println("time[ms]  : "     + time );
        System.out.println();
        System.out.println("result    : "     + result );
        System.out.println("Math.PI   : "     + Math.PI );
        System.out.printf( "Error     : %.1E" , Math.abs( Math.PI - result) );
    }
}

class MonteCarloPICalculator {
    private final String name;
    private final long   nTrials;
    private long         count = 0;
    private long         time;

    private final Random ran = new Random();

    public MonteCarloPICalculator(String name, long nTrials) {
        this.name    = name;
        this.nTrials = nTrials;
    }

    public void calcPI() {
        long start = System.currentTimeMillis();

        for(int i=0; i<nTrials; i++) {
            double x = ran.nextDouble();
            double y = ran.nextDouble();

            if( x*x + y*y < 1.0 ) count++;
        }

        time = System.currentTimeMillis() - start;
    }

    public void printResult() {
        System.out.println("--------------------");
        System.out.println(name);
        System.out.println("nTrials   : " + nTrials);
        System.out.println("count     : " + count);
        System.out.println("time[ms]  : " + time);
        System.out.println("result    : " + count / (double)nTrials * 4.0);
    }

    public long getCount() {
        return count;
    }
}