add examples in java 8 (#12)

* code for chapters 3-9 in Java

* code for chapters 1 in Java

* code for chapter 2 in Java

* missing CheckVoter for chapter 5 in Java

* add missing sample output for SetCovering as a comment

03_recursion/java/01_countdown/src/Countdown.java

@@ -0,0 +1,17 @@
+public class Countdown {
+
+    private static void countdown(int i) {
+        System.out.println(i);
+
+        // base case
+        if (i <= 0) {
+            return;
+        } else {
+            countdown(i - 1);
+        }
+    }
+
+    public static void main(String[] args) {
+        countdown(5);
+    }
+}