* rename file

* create strings directory
* fix docs
* add test

strings/ReverseString.java

@@ -0,0 +1,44 @@
+package strings;
+
+/**
+ * Reverse String using different version
+ */
+public class ReverseString {
+
+    public static void main(String[] args) {
+        assert reverse("abc123").equals("321cba");
+        assert reverse2("abc123").equals("321cba");
+    }
+
+    /**
+     * easiest way to reverses the string str and returns it
+     *
+     * @param str string to be reversed
+     * @return reversed string
+     */
+    public static String reverse(String str) {
+        return new StringBuilder(str).reverse().toString();
+    }
+
+    /**
+     * second way to reverses the string str and returns it
+     *
+     * @param str string to be reversed
+     * @return reversed string
+     */
+    public static String reverse2(String str) {
+
+        if (str == null || str.isEmpty()) {
+            return str;
+        }
+        
+        char[] value = str.toCharArray();
+        for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
+            char temp = value[i];
+            value[i] = value[j];
+            value[j] = temp;
+        }
+        return new String(value);
+    }
+
+}