diff --git a/E_709_ToLowerCase.java b/E_709_ToLowerCase.java
new file mode 100644
index 0000000..4f976c2
--- /dev/null
+++ b/E_709_ToLowerCase.java
@@ -0,0 +1,13 @@
+   public String toLowerCase(String str) {
+        StringBuilder sonuc = new StringBuilder();
+ //stringbuilder kullanarak 0ms, str ve += kullanarak 4ms
+        for (int i = 0; i < str.length(); i++) {
+            int ascii = str.charAt(i);
+            if (ascii <= 90 && ascii >= 65) {
+                sonuc.append((char) (ascii + 32));
+            } else
+                sonuc.append((char) ascii);
+
+        }
+        return sonuc.toString();
+    }
\ No newline at end of file