implement validateEmail function in BonusExercises

src/main/java/BonusExercises.java

@@ -5,22 +5,8 @@ import java.util.regex.Pattern;
 
 public class BonusExercises {
 
-    /*
-        complete the method below, so it will validate an email address
-        1. Must have exactly one @ (no more, no less)
-        2. Split into local-part and domain (before @ and after @)
-        3. Local-part rules:
-            - Can't be empty
-            - Can't start or end with dot
-            - Can't have two dots in a row
-        4. Domain rules:
-            - Can't be empty
-            - Can't start or end with hyphen
-            - Can't have underscores
-            - Each segment (between dots) must follow same hyphen rules
-     */
     public boolean validateEmail(String email) {
-        String regex = ""; // todo
+        String regex = "^[a-zA-Z0-9]+[a-zA-Z0-9._]*@[a-zA-Z0-9]+[a-zA-Z0-9-]*(\\.[a-zA-Z]+)+$";
         Pattern pattern = Pattern.compile(regex);
         Matcher matcher = pattern.matcher(email);