* Added arithmetic series

* Fixed compare two double
* Fiexed documentation

Author: realDuYuanChao

Maths/Area.java

@@ -5,31 +5,31 @@
  */
 public class Area {
     public static void main(String[] args) {
+        
         /* test cube */
-        assert surfaceAreaCube(1) == 6;
+        assert Double.compare(surfaceAreaCube(1), 6.0) == 0;
 
         /* test sphere */
-        assert surfaceAreaSphere(5) == 314.1592653589793;
-        assert surfaceAreaSphere(1) == 12.566370614359172;
+        assert Double.compare(surfaceAreaSphere(5), 314.1592653589793) == 0;
+        assert Double.compare(surfaceAreaSphere(1), 12.566370614359172) == 0;
 
         /* test rectangle */
-        assert surfaceAreaRectangle(10, 20) == 200;
+        assert Double.compare(surfaceAreaRectangle(10, 20), 200.0) == 0;
 
         /* test square */
-        assert surfaceAreaSquare(10) == 100;
+        assert Double.compare(surfaceAreaSquare(10), 100.0) == 0;
 
         /* test triangle */
-        assert surfaceAreaTriangle(10, 10) == 50;
+        assert Double.compare(surfaceAreaTriangle(10, 10), 50.0) == 0;
 
         /* test parallelogram */
-        assert surfaceAreaParallelogram(10, 20) == 200;
+        assert Double.compare(surfaceAreaParallelogram(10, 20), 200.0) == 0;
 
         /* test trapezium */
-        assert surfaceAreaTrapezium(10, 20, 30) == 450;
+        assert Double.compare(surfaceAreaTrapezium(10, 20, 30), 450.0) == 0;
 
         /* test circle */
-        assert surfaceAreaCircle(20) == 1256.6370614359173;
-
+        assert Double.compare(surfaceAreaCircle(20), 1256.6370614359173) == 0;
     }
 
     /**
@@ -38,7 +38,7 @@ public static void main(String[] args) {
      * @param sideLength side length of cube
      * @return surface area of given cube
      */
-    public static double surfaceAreaCube(double sideLength) {
+    private static double surfaceAreaCube(double sideLength) {
         return 6 * sideLength * sideLength;
     }
 
@@ -48,7 +48,7 @@ public static double surfaceAreaCube(double sideLength) {
      * @param radius radius of sphere
      * @return surface area of given sphere
      */
-    public static double surfaceAreaSphere(double radius) {
+    private static double surfaceAreaSphere(double radius) {
         return 4 * Math.PI * radius * radius;
     }
 
@@ -59,7 +59,7 @@ public static double surfaceAreaSphere(double radius) {
      * @param width  width of rectangle
      * @return area of given rectangle
      */
-    public static double surfaceAreaRectangle(double length, double width) {
+    private static double surfaceAreaRectangle(double length, double width) {
         return length * width;
     }
 
@@ -69,7 +69,7 @@ public static double surfaceAreaRectangle(double length, double width) {
      * @param sideLength side length of square
      * @return area of given square
      */
-    public static double surfaceAreaSquare(double sideLength) {
+    private static double surfaceAreaSquare(double sideLength) {
         return sideLength * sideLength;
     }
 
@@ -80,7 +80,7 @@ public static double surfaceAreaSquare(double sideLength) {
      * @param height height of triangle
      * @return area of given triangle
      */
-    public static double surfaceAreaTriangle(double base, double height) {
+    private static double surfaceAreaTriangle(double base, double height) {
         return base * height / 2;
     }
 
@@ -91,7 +91,7 @@ public static double surfaceAreaTriangle(double base, double height) {
      * @param height height of parallelogram
      * @return area of given parallelogram
      */
-    public static double surfaceAreaParallelogram(double base, double height) {
+    private static double surfaceAreaParallelogram(double base, double height) {
         return base * height;
     }
 
@@ -103,7 +103,7 @@ public static double surfaceAreaParallelogram(double base, double height) {
      * @param height height of trapezium
      * @return area of given trapezium
      */
-    public static double surfaceAreaTrapezium(double base1, double base2, double height) {
+    private static double surfaceAreaTrapezium(double base1, double base2, double height) {
         return (base1 + base2) * height / 2;
     }
 
@@ -113,7 +113,7 @@ public static double surfaceAreaTrapezium(double base1, double base2, double hei
      * @param radius radius of circle
      * @return area of given circle
      */
-    public static double surfaceAreaCircle(double radius) {
+    private static double surfaceAreaCircle(double radius) {
         return Math.PI * radius * radius;
     }
-}
+}

Maths/PowRecursion.java

@@ -2,10 +2,10 @@
 
 public class PowRecursion {
     public static void main(String[] args) {
-        assert pow(2, 0) == Math.pow(2, 0);
-        assert pow(0, 2) == Math.pow(0, 2);
-        assert pow(2, 10) == Math.pow(2, 10);
-        assert pow(10, 2) == Math.pow(10, 2);
+        assert Double.compare(pow(2, 0), Math.pow(2, 0)) == 0;
+        assert Double.compare(pow(0, 2), Math.pow(0, 2)) == 0;
+        assert Double.compare(pow(2, 10), Math.pow(2, 10)) == 0;
+        assert Double.compare(pow(10, 2), Math.pow(10, 2)) == 0;
     }
 
     /**
@@ -17,10 +17,6 @@ public static void main(String[] args) {
      * @return the value {@code a}<sup>{@code b}</sup>.
      */
     public static long pow(int a, int b) {
-        if (b == 0) {
-            return 1;
-        } else {
-            return a * pow(a, b - 1);
-        }
+        return b == 0 ? 1 : a * pow(a, b - 1);
     }
-}
+}

Maths/SumOfArithmeticSeries.java

@@ -0,0 +1,40 @@
+package Maths;
+
+/**
+ * <p>
+ * In mathematics, an arithmetic progression (AP) or arithmetic sequence is a sequence of numbers such that the
+ * difference between the consecutive terms is constant. Difference here means the second minus the first.
+ * For instance, the sequence 5, 7, 9, 11, 13, 15, . . . is an arithmetic progression with common difference of 2.
+ * <p>
+ * Wikipedia: https://en.wikipedia.org/wiki/Arithmetic_progression
+ */
+public class SumOfArithmeticSeries {
+    public static void main(String[] args) {
+
+        /* 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 */
+        assert Double.compare(55.0, sumOfSeries(1, 1, 10)) == 0;
+
+        /* 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 */
+        assert Double.compare(100.0, sumOfSeries(1, 2, 10)) == 0;
+
+        /* 1 + 11 + 21 + 31 + 41 + 51 + 61 + 71 + 81 + 91 */
+        assert Double.compare(460.0, sumOfSeries(1, 10, 10)) == 0;
+
+        /* 0.1 + 0.2 + 0.3 + 0.4 + 0.5 + 0.6 + 0.7 + 0.8 + 0.9 + 1.0 */
+        assert Double.compare(5.5, sumOfSeries(0.1, 0.1, 10)) == 0;
+
+        assert Double.compare(49600.0, sumOfSeries(1, 10, 100)) == 0;
+    }
+
+    /**
+     * Calculate sum of arithmetic series
+     *
+     * @param firstTerm  the initial term of an arithmetic series
+     * @param commonDiff the common difference of an arithmetic series
+     * @param numOfTerms the total terms of an arithmetic series
+     * @return sum of given arithmetic series
+     */
+    private static double sumOfSeries(double firstTerm, double commonDiff, int numOfTerms) {
+        return numOfTerms / 2.0 * (2 * firstTerm + (numOfTerms - 1) * commonDiff);
+    }
+}