Solving the kata bouncing ball

src/main/java/org/fundacionjala/coding/abel/BouncingBall.java

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+package org.fundacionjala.coding.abel;
+
+/**
+ * A child plays with a ball on the nth floor of a big building. The height of this floor is known:
+ * (float parameter "h" in meters, h > 0) .
+ * He lets out the ball. The ball rebounds for example to two-thirds:
+ * (float parameter "bounce", 0 < bounce < 1)
+ * of its height.
+ * His mother looks out of a window that is 1.5 meters from the ground:
+ * (float parameters window < h).
+ * How many times will the mother see the ball either falling or bouncing in front of the window
+ * (return a positive integer unless conditions are not fulfilled in which case return -1) ?
+ * Note
+ * You will admit that the ball can only be seen if the height of the rebouncing ball is stricty greater
+ * than the window parameter.
+ * Example:
+ * h = 3, bounce = 0.66, window = 1.5, result is 3
+ * h = 3, bounce = 1, window = 1.5, result is -1
+ */
+public final class BouncingBall {
+
+    /**
+     * Private Constructor.
+     */
+    private BouncingBall() {
+
+    }
+
+    /**
+     * Calculates how many times the ball is seen throw the window.
+     *
+     * @param h      Initial Height of the ball.
+     * @param bounce Bounce rate.
+     * @param window Windows's Height.
+     * @return How many times the ball is seen.
+     */
+    public static int bouncingBall(double h, double bounce, double window) {
+        if (!(h > 0 && 0 < bounce && bounce < 1 && window < h)) {
+            return -1;
+        }
+        int count = 1;
+        while (h * bounce >= window) {
+            count += 2;
+            h = h * bounce;
+        }
+        return count;
+    }
+}

src/test/java/org/fundacionjala/coding/abel/BouncingBallTest.java

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+package org.fundacionjala.coding.abel;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Modifier;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test class for Bouncing Ball.
+ */
+public class BouncingBallTest {
+
+    /**
+     * Test for Private Constructors.
+     *
+     * @throws NoSuchMethodException     Thrown when a particular method cannot be found.
+     * @throws IllegalAccessException    Thrown when an application tries to reflectively create an instance.
+     * @throws InvocationTargetException thrown by an invoked method or constructor.
+     * @throws InstantiationException    Thrown when an application tries to create an instance of a class
+     *                                   using the {@code newInstance} method in class.
+     */
+    @Test
+    public void privateConstructorTest() throws NoSuchMethodException, IllegalAccessException,
+            InvocationTargetException, InstantiationException {
+        Constructor<BouncingBall> constructor = BouncingBall.class.getDeclaredConstructor();
+        assertTrue(Modifier.isPrivate(constructor.getModifiers()));
+        constructor.setAccessible(true);
+        constructor.newInstance();
+    }
+
+    /**
+     * First Test.
+     */
+    @Test
+    public void test1() {
+        assertEquals(3, BouncingBall.bouncingBall(3.0, 0.66, 1.5));
+    }
+
+    /**
+     * Second Test.
+     */
+    @Test
+    public void test2() {
+        assertEquals(15, BouncingBall.bouncingBall(30.0, 0.66, 1.5));
+    }
+
+    /**
+     * Third Test.
+     */
+    @Test
+    public void test3() {
+        assertEquals(-1, BouncingBall.bouncingBall(1.0, 0.66, 2.00));
+    }
+}