1 /*
   2  * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  *   - Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  *
  11  *   - Redistributions in binary form must reproduce the above copyright
  12  *     notice, this list of conditions and the following disclaimer in the
  13  *     documentation and/or other materials provided with the distribution.
  14  *
  15  *   - Neither the name of Oracle nor the names of its
  16  *     contributors may be used to endorse or promote products derived
  17  *     from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  20  * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  24  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  25  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  26  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  27  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  28  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  29  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31 
  32 /*
  33  * This source code is provided to illustrate the usage of a given feature
  34  * or technique and has been deliberately simplified. Additional steps
  35  * required for a production-quality application, such as security checks,
  36  * input validation and proper error handling, might not be present in
  37  * this sample code.
  38  */
  39 package stream.parallel;
  40 
  41 import java.util.concurrent.ThreadLocalRandom;
  42 import java.util.stream.LongStream;
  43 
  44 /**
  45  * This demo shows how to use the parallel mode and the Monte Carlo method to
  46  * calculate the value of PI
  47  *
  48  * @author tyan
  49  */
  50 public class MonteCarloPI {
  51 
  52     public static void main(String[] args) {
  53         System.out.println("This might take several minutes, "
  54                 + "depending on your system");
  55         LongStream.iterate(10l, l -> 10 * l).
  56                 limit(10).
  57                 forEach(times -> {
  58                     System.out.printf(
  59                             "The value of PI is %1.14f after %,d times calculation\n",
  60                             pi(times), times);
  61                 });
  62     }
  63 
  64     /**
  65      * Use the Monte Carlo method to calculate the value of PI. basic algorithm
  66      * is: 1. Draw a square on the ground, then inscribe a circle within it. 2.
  67      * Scatter some objects of uniform size (grains of rice or sand) over the
  68      * square. 3. Count the total number of objects inside the circle and the
  69      * total number of objects overall. 4. The ratio of the two total is an
  70      * estimate of the ratio of the two areas, which is PI/4. Multiply the
  71      * result by 4 to estimate PI.
  72      *
  73      * @param x how many times randomly selected a point
  74      * @return value of π by x times calculation
  75      */
  76     private static double pi(long N) {
  77         long M = LongStream.range(0, N).parallel().filter(sr -> {
  78             // Random picked up point to check if it's in the circle.
  79             double x = ThreadLocalRandom.current().nextDouble(-1, 1);
  80             double y = ThreadLocalRandom.current().nextDouble(-1, 1);
  81 
  82             return x * x + y * y < 1.0 * 1.0;  // Not using
  83         }).count();
  84         return 4.0 * M / N;
  85     }
  86 
  87     /**
  88      * Use ThreadLocalRandom to simulate that whether a point is inside the
  89      * circle or outside the circle
  90      *
  91      * @return 1 randomly selected point is inside the circle 0 randomly
  92      * selected point is outside the circle
  93      */
  94     private static long hit() {
  95         ThreadLocalRandom lr = ThreadLocalRandom.current();
  96         double x = lr.nextDouble(1.0);
  97         double y = lr.nextDouble(1.0);
  98         return Math.sqrt(y * y + x * x) <= 1.0 ? 1 : 0;
  99     }
 100 }