优化JavaS进一步完善细节

src/META-INF/MANIFEST.MF

@@ -0,0 +1,3 @@
+Manifest-Version: 1.0
+Main-Class: com.mathpaper.main.Main
+

src/com/mathpaper/user/Account.java

@@ -1,5 +1,7 @@
 package com.mathpaper.user;
 
+import java.util.Set;
+
 public class Account {
     private String username;
     private String password;
@@ -7,6 +9,9 @@ public class Account {
 
     // 构造方法
     public Account(String username, String password, String type) {
+        if (!Set.of("小学", "初中", "高中").contains(type)) {
+            throw new IllegalArgumentException("无效的学段类型");
+        }
         this.username = username;
         this.password = password;
         this.type = type;