diff --git a/JavaOOP/lib/gson-2.8.6.jar b/JavaOOP/lib/gson-2.8.6.jar
new file mode 100644
index 00000000..4765c4af
Binary files /dev/null and b/JavaOOP/lib/gson-2.8.6.jar differ
diff --git a/JavaOOP/src/Java16.java b/JavaOOP/src/Java16.java
index b6d4c177..921e7046 100644
--- a/JavaOOP/src/Java16.java
+++ b/JavaOOP/src/Java16.java
@@ -1,2 +1,12 @@
+import object.OverLoad;
+
 public class Java16 {
+    public static void main(String[] args) {
+
+        OverLoad ov = new OverLoad();
+
+        ov.hap(20, 50); // hap_int_int(20, 50)
+        ov.hap(23.4f, 56); // hap_float_int(23.4f, 56)
+        ov.hap(56.7f, 78.9f); // hap_float_float(56.7f, 78.9f)
+    }
 }
diff --git a/JavaOOP/src/Java17.java b/JavaOOP/src/Java17.java
new file mode 100644
index 00000000..c44b1653
--- /dev/null
+++ b/JavaOOP/src/Java17.java
@@ -0,0 +1,28 @@
+import com.google.gson.Gson;
+import object.BookVO;
+import object.MyUtil;
+
+public class Java17 {
+    public static void main(String[] args) {
+
+        // 1. Java 에서 제공해주는 class 들 -> API
+        String str = new String("apple");
+        // new String 생략 가능
+        String str1 = "apple";
+        System.out.println(str1.toUpperCase()); // 소문자 -> 대문자 변환 메소드
+
+        // 2. 직접 만들어서 사용하는 class 들 -> DTO/VO, DAO, Utility ... API
+        MyUtil my = new MyUtil();
+        int sum1to10 = my.hap();
+        System.out.println(sum1to10);
+
+        // 3. 다른 회사(사람) 에서 만들어 놓은 class
+        // Gson 사용해보기 : object -> json 형태로 바꿔주는 API
+        Gson g = new Gson();
+        BookVO vo = new BookVO("자바", 13000, "출판사", 800);
+        String json = g.toJson(vo);
+
+        System.out.println(json);
+    }
+}
+
diff --git a/JavaOOP/src/object/MyUtil.java b/JavaOOP/src/object/MyUtil.java
new file mode 100644
index 00000000..19bcafc6
--- /dev/null
+++ b/JavaOOP/src/object/MyUtil.java
@@ -0,0 +1,11 @@
+package object;
+
+public class MyUtil {
+    public int hap() {
+        int sum = 0;
+        for (int i = 1; i <= 10; i++) {
+            sum += i;
+        }
+        return sum;
+    }
+}
diff --git a/JavaOOP/src/object/OverLoad.java b/JavaOOP/src/object/OverLoad.java
new file mode 100644
index 00000000..1b987a6a
--- /dev/null
+++ b/JavaOOP/src/object/OverLoad.java
@@ -0,0 +1,14 @@
+package object;
+
+public class OverLoad {
+    // 동작(method)으로만 이루어진 객체
+    public void hap(int a, int b){
+        System.out.println(a+b);
+    }
+    public void hap(float a, int b){
+        System.out.println(a+b);
+    }
+    public void hap(float a, float b){
+        System.out.println(a+b);
+    }
+}