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);
+    }
+}

03_recursion/java/02_greet/src/Greet.java

@@ -0,0 +1,21 @@
+public class Greet {
+
+    private static void greet2(String name) {
+        System.out.println("how are you, " + name + "?");
+    }
+
+    private static void bye() {
+        System.out.println("ok bye!");
+    }
+
+    private static void greet(String name) {
+        System.out.println("hello, " + name + "!");
+        greet2(name);
+        System.out.println("getting ready to say bye...");
+        bye();
+    }
+
+    public static void main(String[] args) {
+        greet("adit");
+    }
+}

03_recursion/java/03_factorial/src/Factorial.java

@@ -0,0 +1,14 @@
+public class Factorial {
+
+    private static int fact(int x) {
+        if (x == 1) {
+            return 1;
+        } else {
+            return x * fact(x - 1);
+        }
+    }
+
+    public static void main(String[] args) {
+        System.out.println(fact(5));
+    }
+}