Collatz Sequence

Maths/CollatzSequence.java

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+package Maths;
+
+/**
+ * The Collatz conjecture is a conjecture in mathematics that concerns a sequence defined as follows:
+ * start with any positive integer n.
+ * Then each term is obtained from the previous term as follows:
+ * if the previous term is even, the next term is one half of the previous term.
+ * If the previous term is odd, the next term is 3 times the previous term plus 1.
+ * The conjecture is that no matter what value of n, the sequence will always reach 1.
+ * <a href="https://www.wikiwand.com/en/Collatz_conjecture">https://www.wikiwand.com/en/Collatz_conjecture</a>
+ */
+public class CollatzSequence {
+    /**
+     * Runs the sequence starting on the value passed in, stopping when the sequence reaches 1.
+     * @param start initial value the sequence is run on.
+     */
+    public static void collatz(int start) {
+        while (start != 1) {
+            System.out.print(start + " ");
+            if (start % 2 == 0) {
+                start = start / 2;
+            }
+            else {
+                start = 3 * start + 1;
+            }
+        }
+        System.out.print(start);
+        System.out.println();
+    }
+
+    /**
+     * Driver code
+     */
+    public static void main(String[] args) {
+        collatz(3); // 3, 10, 5, 16, 8, 4, 2, 1
+        collatz(6); // 6, 3, 10, 5, 16, 8, 4, 2, 1
+    }
+}

Maths/HeronsFormula.java

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+package Maths;
+
+/**
+ * Heron's formula gives the area of a triangle when the length of all three sides are known.
+ * <a href="https://www.wikiwand.com/en/Heron%27s_formula">https://www.wikiwand.com/en/Heron%27s_formula</a>
+ */
+
+public class HeronsFormula {
+    /**
+     *
+     * @param a a side of the triangle
+     * @param b a side of the triangle
+     * @param c a side of the triangle
+     * @return the calculated area of the triangle using Heron's formula
+     */
+    public static double calculateArea(double a, double b, double c) {
+        /* Checks if the three sides can really represent a triangle */
+        if ((a + b < c) || (b + c < a) || (a + c < b)) {
+            return 0.0;
+        }
+
+        double halfPerimeter = (a + b + c) / 2.0;
+        double area = Math.sqrt(halfPerimeter * (halfPerimeter - a) * (halfPerimeter - b) * (halfPerimeter - c));
+
+        return area;
+    }
+    /**
+     * Driver code
+     */
+    public static void main(String[] args) {
+        assert calculateArea(5, 5, 5) == 10.825317547305483;
+        assert calculateArea(4, 4, 5) == 7.806247497997997;
+        assert calculateArea(10, 2, 3) == 0.0;
+    }
+}