BAEL-4405 Probability in Java

java-numbers-3/src/main/java/com/baeldung/probability/MaleHeightGenerator.java

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+package com.baeldung.probability;
+
+import org.apache.commons.math3.distribution.NormalDistribution;
+
+public class MaleHeightGenerator {
+    private static final double MEAN_HEIGHT = 176.02;
+    private static final double STANDARD_DEVIATION = 7.11;
+    private static NormalDistribution distribution =  new NormalDistribution(MEAN_HEIGHT, STANDARD_DEVIATION);
+
+    public static double generateNormalHeight() {
+        return distribution.sample();
+    }
+
+    public static double probabilityOfHeightBetween(double heightLowerExclusive, double heightUpperInclusive) {
+        return distribution.probability(heightLowerExclusive, heightUpperInclusive);
+    }
+}

java-numbers-3/src/main/java/com/baeldung/probability/RandomInvoker.java

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+package com.baeldung.probability;
+
+import io.vavr.Lazy;
+
+import java.util.SplittableRandom;
+import java.util.function.Supplier;
+
+public class RandomInvoker {
+    private final Lazy<SplittableRandom> random = Lazy.of(SplittableRandom::new);
+
+    public <T> T withProbability(Supplier<T> supplier1, Supplier<T> supplier2, int probability) {
+        SplittableRandom random = this.random.get();
+        if (random.nextInt(1, 101) <= probability) {
+            return supplier1.get();
+        } else {
+            return supplier2.get();
+        }
+    }
+}

java-numbers-3/src/test/java/com/baeldung/probability/RandomInvokerUnitTest.java

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+package com.baeldung.probability;
+
+import org.assertj.core.data.Offset;
+import org.junit.Test;
+
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class RandomInvokerUnitTest {
+    @Test
+    public void givenProbability_whenInvoked_invokeWithProbability() {
+        RandomInvoker randomInvoker = new RandomInvoker();
+
+        int numberOfSamples = 1_000_000;
+        int probability = 10;
+        int howManyTimesInvoked = Stream.generate(() -> randomInvoker.withProbability(() -> 1, () -> 0, probability))
+                .limit(numberOfSamples)
+                .mapToInt(e -> e).sum();
+        int monteCarloProbability = (howManyTimesInvoked * 100) / numberOfSamples;
+
+        assertThat(monteCarloProbability).isCloseTo(probability, Offset.offset(1));
+    }
+}