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 }