获取用户对象

src/main/java/mathlearning/service/UserService.java

@@ -172,4 +172,9 @@ public class UserService {
     public boolean isValidEmail(String email) {
         return email.matches("^[A-Za-z0-9+_.-]+@(.+)$");
     }
+
+    public User getUser(String email ) {
+        User user = users.get(email);
+        return user;
+    }
 }

src/main/java/mathlearning/ui/LoginFrame.java

@@ -102,10 +102,10 @@ public class LoginFrame extends JFrame{
     }
 
     private void openMainFrame(String email) {
-
+        User user = userService.getUser(email);
         // 这里先简单显示一个消息，后续可以扩展为主界面
         JOptionPane.showMessageDialog(this,
-                "欢迎 " + email + "!\n登录成功，主界面功能待实现。",
+                "欢迎 " + user.getUsername() + "!\n登录成功，主界面功能待实现。",
                 "登录成功", JOptionPane.INFORMATION_MESSAGE);
     }
 }