v3.3 对前端长方法进行解耦，并使代码符合规范

src/main/java/com/wsf/mathapp/view/RegisterView.java

@@ -254,7 +254,7 @@ public class RegisterView {
    * @return boolean 用户名是否有效.
    */
   private boolean validateUsernameForCode(String username) {
-    if (!isValidUsername(username)) {
+    if (isInvalidUsername(username)) {
       showError(statusLabel, "用户名只包含英文字母和数字)");
       return false;
     }
@@ -338,7 +338,7 @@ public class RegisterView {
    */
   private boolean validateRegistrationInput(String username, String email,
       String code, String password, String confirmPassword) {
-    if (!isValidUsername(username)) {
+    if (isInvalidUsername(username)) {
       showError(statusLabel, "用户名只包含英文字母和数字");
       return false;
     }
@@ -393,9 +393,7 @@ public class RegisterView {
       try {
         for (int i = 60; i > 0; i--) {
           int finalI = i;
-          javafx.application.Platform.runLater(() -> {
-            button.setText(finalI + "秒后重发");
-          });
+          javafx.application.Platform.runLater(() -> button.setText(finalI + "秒后重发"));
           Thread.sleep(1000);
         }
         javafx.application.Platform.runLater(() -> {
@@ -436,13 +434,13 @@ public class RegisterView {
    * @param username 用户名.
    * @return boolean 用户名格式是否有效.
    */
-  public static boolean isValidUsername(String username) {
+  public static boolean isInvalidUsername(String username) {
     if (username == null || username.trim().isEmpty()) {
-      return false;
+      return true;
     }
     // 用户名规则：只包含英文字母和数字，不限制长度
     String usernameRegex = "^[a-zA-Z0-9]+$";
-    return Pattern.matches(usernameRegex, username.trim());
+    return !Pattern.matches(usernameRegex, username.trim());
   }
 
   /**