diff --git a/ch04/GraphicsTest.java b/ch04/GraphicsTest.java
new file mode 100644
index 0000000..46630b8
--- /dev/null
+++ b/ch04/GraphicsTest.java
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+import java.awt.Canvas;
+import java.awt.Graphics;
+import java.awt.Color;
+import javax.swing.JFrame;
+import java.util.Random;
+import java.text.DecimalFormat;
+
+/**
+ * Graphics Test
+ */
+
+public class GraphicsTest extends Canvas {
+
+    public static void main(String[] args) {
+        JFrame frame = new JFrame("Graphics Test");
+        Canvas GraphicsTest = new GraphicsTest();
+        GraphicsTest.setSize(256, 256);
+        GraphicsTest.setBackground(Color.BLACK);
+        frame.add(GraphicsTest);
+        frame.pack();
+        frame.setVisible(true);
+    }
+
+    public void paint(Graphics g) {
+        double angle = 0.0;
+        for (int x = 0; x <= 1024; x += 8) {
+
+            // Set y-position from sin of angle.
+            double y = 64 + (Math.sin(angle) * 55.0);
+
+            // generate a random color with HSB.
+            Random r = new Random();
+            double hue = r.nextDouble();
+            float h = (float) hue; // hue
+            float s = (float) 1.0; // saturation
+            float b = (float) 1.0; // brightness
+
+            // Set color and draw rectangle.
+            Color rainbow = Color.getHSBColor(h, s, b);
+            g.setColor(rainbow);
+            g.fillRect(x, (int)y, 5, 100);
+            g.fillOval(x * 2, ((int)y+200), 32, 32);
+
+            // Update angle for next ineration.
+            angle += Math.PI/12.0;
+
+        }
+    }
+}
+
+
+//        double root = Math.sqrt(17.0);
+//        double angle = 1.5;
+//        double height = Math.sin(angle);
+
+//        double degrees = 90;
+//        double angle2 = degrees / 180.0 * Math.PI;
+//        double radians = Math.toRadians(180.0);
+//        double degrees2 = Math.toDegrees(Math.PI);
+//        long x = Math.round(Math.PI * 20.0);
+
+//        double x2 = Math.cos(angle + Math.PI / 2.0);
+//        double x3 = Math.exp(Math.log(10.0));
+//        double x4 = Math.pow(2.0, 10.0);
+//        System.out.println(x4);
+
diff --git a/ch04/TestClass.java b/ch04/TestClass.java
new file mode 100644
index 0000000..eec7e1d
--- /dev/null
+++ b/ch04/TestClass.java
@@ -0,0 +1,23 @@
+/**
+ * Examples from Chapter 4.
+ */
+public class TestClass {
+
+    public static void main(String[] args) {
+        double root = Math.sqrt(17.0);
+        double angle = 1.5;
+        double height = Math.sin(angle);
+
+        double degrees = 90;
+        double angle2 = degrees / 180.0 * Math.PI;
+        double radians = Math.toRadians(180.0);
+        double degrees2 = Math.toDegrees(Math.PI);
+        long x = Math.round(Math.PI * 20.0);
+
+        double x2 = Math.cos(angle + Math.PI / 2.0);
+        double x3 = Math.exp(Math.log(10.0));
+        double x4 = Math.pow(2.0, 10.0);
+        System.out.println(x2);
+    }
+
+}