Refactor the validator.

src/main/java/space/kklochko/jdbc_hospital_example/cli/validators/InputStringFormatValidator.java

@@ -4,7 +4,7 @@ import java.util.regex.Pattern;
 
 public class InputStringFormatValidator extends Validator {
     String command;
-    String formatRegEx = "\\w+\\s\\w+\\((|[^)]+)\\)";
+    String formatRegEx = "\\w+\\s\\w+\\([^)]*\\)";
 
     public InputStringFormatValidator(String command) {
         this.command = command;

src/main/java/space/kklochko/jdbc_hospital_example/cli/validators/Validator.java

@@ -0,0 +1,9 @@
+package space.kklochko.jdbc_hospital_example.cli.validators;
+
+import java.util.regex.Pattern;
+
+abstract public class Validator {
+    abstract public boolean isValid();
+
+    abstract public String getMessage();
+}