diff --git "a/\352\271\200\354\225\204\353\246\260/java-basic/src/poly/basic/CastingMain4.java" "b/\352\271\200\354\225\204\353\246\260/java-basic/src/poly/basic/CastingMain4.java"
new file mode 100644
index 0000000..f56a10f
--- /dev/null
+++ "b/\352\271\200\354\225\204\353\246\260/java-basic/src/poly/basic/CastingMain4.java"
@@ -0,0 +1,15 @@
+package poly.basic;
+
+// 다운 캐스팅을 자동으로 하지 않는 이유
+public class CastingMain4 {
+    public static void main(String[] args) {
+        Parent parent1 = new Child();
+        Child child1 = (Child) parent1;
+        child1.childMethod();   // 문제 없음
+
+        Parent parent2 = new Parent();
+        
+        Child child2 = (Child) parent2; // 런타임 오류 - ClassCastException
+        child2.childMethod();   // 실행 불가
+    }
+}