build error "incompatible types: possible lossy conversion from int to char"

Cause unknown: Not use Java11 public static String java.lang.Character.toString( int codePoint )

Author: remixgrjp

.idea/gradle.xml

@@ -23,8 +23,8 @@ android {
         }
     }
     compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_8
-        targetCompatibility JavaVersion.VERSION_1_8
+        sourceCompatibility JavaVersion.VERSION_11
+        targetCompatibility JavaVersion.VERSION_11
     }
 }
 

.idea/vcs.xml

@@ -9,5 +9,9 @@ public class MainActivity extends AppCompatActivity{
 	protected void onCreate( Bundle savedInstanceState ){
 		super.onCreate( savedInstanceState );
 		setContentView( R.layout.activity_main );
+
+		int i = 0x20BB7;//surrogate pair Unicode
+		String str = java.lang.Character.toString( i );//Java 11
+
 	}
 }