Add IFS java implementation (#817)

Author: stormofice

contents/IFS/IFS.md

@@ -140,6 +140,8 @@ Here, instead of tracking children of children, we track a single individual tha
 [import:18-29, lang:"c"](code/c/IFS.c)
 {% sample lang="coco" %}
 [import:4-16, lang:"coconut"](code/coconut/IFS.coco)
+{% sample lang="java" %}
+[import:16-39, lang:"java"](code/java/IFS.java)
 {% endmethod %}
 
 If we set the initial point to the on the equilateral triangle we saw before, we can see the Sierpinski triangle again after a few thousand iterations, as shown below:
@@ -220,6 +222,8 @@ In addition, we have written the chaos game code to take in a set of points so t
 [import, lang:"c"](code/c/IFS.c)
 {%sample lang="coco" %}
 [import, lang:"coconut"](code/coconut/IFS.coco)
+{%sample lang="java" %}
+[import, lang:"java"](code/java/IFS.java)
 {% endmethod %}
 
 ### Bibliography

contents/IFS/code/java/IFS.java

@@ -0,0 +1,61 @@
+import java.io.FileWriter;
+import java.util.Random;
+
+public class IFS {
+
+    private static class Point {
+        double x, y;
+
+        public Point(double x, double y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+    
+    // This is a function to simulate a "chaos game"
+    public static Point[] chaosGame(int n, Point[] shapePoints) {
+        Random rng = new Random();
+
+        // Initialize output vector
+        Point[] outputPoints = new Point[n];
+
+        // Choose first point randomly
+        Point point = new Point(rng.nextDouble(), rng.nextDouble());
+
+        for (int i = 0; i < n; i++) {
+            outputPoints[i] = point;
+
+            // Clone point to get a new reference
+            point = new Point(point.x, point.y);
+
+            // Retrieve random shape point
+            Point temp = shapePoints[rng.nextInt(shapePoints.length)];
+            // Calculate midpoint
+            point.x = 0.5 * (point.x + temp.x);
+            point.y = 0.5 * (point.y + temp.y);
+        }
+
+        return outputPoints;
+    }
+
+    public static void main(String[] args) throws Exception {
+        // This will generate a Sierpinski triangle with a chaos game of n points for an
+        // initial triangle with three points on the vertices of an equilateral triangle:
+        //     A = (0.0, 0.0)
+        //     B = (0.5, sqrt(0.75))
+        //     C = (1.0, 0.0)
+        // It will output the file sierpinski.dat, which can be plotted after
+        Point[] shapePoints = new Point[]{
+                new Point(0.0, 0.0),
+                new Point(0.5, Math.sqrt(0.75)),
+                new Point(1.0, 0.0)
+        };
+        Point[] outputPoints = chaosGame(10000, shapePoints);
+
+        FileWriter fw = new FileWriter("sierpinski.dat");
+        for (Point p : outputPoints)
+            fw.write(p.x + "\t" + p.y + "\n");
+        fw.close();
+    }
+
+}