adding nature of code examples

java/examples/Books/Nature of Code/introduction/SimpleProbablility/SimpleProbablility.pde

@@ -0,0 +1,34 @@
+// Daniel Shiffman
+// The Nature of Code
+// http://www.shiffman.net/
+
+int x,y;
+
+void setup() {
+  size(200,200);
+  background(0);
+  smooth();
+}
+
+void draw() {
+  //create an alpha blended background
+  fill(0,1);
+  rect(0,0,width,height);
+  
+  //calculate a probability between 0 and 100% based on mouseX location
+  float prob = (mouseX / (float) width);     
+  
+  //get a random floating point value between 0 and 1
+  float r = random(1);   
+  
+  //test the random value against the probability and trigger an event
+  if (r < prob) {
+    noStroke();
+    fill(255);
+    ellipse(x,y,10,10);
+  }
+  
+  // X and Y walk through a grid
+  x = (x + 10) % width;
+  if (x == 0) y = (y + 10) % width;
+}