Update ConstAndReadonlyExercise

DotNetGuidePractice/HelloDotNetGuide/CSharp语法/ConstAndReadonlyExercise.cs

@@ -0,0 +1,69 @@
+namespace HelloDotNetGuide.CSharp语法
+{
+    public enum UserRole
+    {
+        Admin,
+        User,
+        Guest
+    }
+
+    public class ConstAndReadonlyExercise
+    {
+        // const 初始化
+        public const int MaxCount = 0;
+        public const UserRole CurrentUserRole = UserRole.Admin;
+
+        // readonly 初始化
+        public readonly string _applicationName;
+
+        public ConstAndReadonlyExercise()
+        {
+            _applicationName = "HelloDotNetGuide_V2";
+        }
+
+        // 懒汉式单例模式示例
+        private static ConstAndReadonlyExercise? _instance;
+        private static readonly object _lockObj = new object();
+
+        public static ConstAndReadonlyExercise Instance
+        {
+            get
+            {
+                if (_instance == null)
+                {
+                    lock (_lockObj)
+                    {
+                        _instance ??= new ConstAndReadonlyExercise();
+                    }
+                }
+                return _instance;
+            }
+        }
+
+        /// <summary>
+        /// 反射修改 readonly 字段的值
+        /// </summary>
+        public static void UpdateApplicationNameValue()
+        {
+            var instance = new ConstAndReadonlyExercise();
+            Console.WriteLine($"初始值: {instance._applicationName}");
+            // 输出: 初始值: HelloDotNetGuide_V2
+
+            var field = instance.GetType().GetField("_applicationName");
+            field.SetValue(instance, "HelloDotNetGuide_V3");
+
+            Console.WriteLine($"修改后: {instance._applicationName}");
+            // 输出: 修改后: HelloDotNetGuide_V3
+        }
+
+        /// <summary>
+        /// 打印所有常量和只读字段的值
+        /// </summary>
+        public static void PrintAllValues()
+        {
+            Console.WriteLine($"MaxCount: {MaxCount}");
+            Console.WriteLine($"CurrentUserRole: {CurrentUserRole}");
+            Console.WriteLine($"ApplicationName: {Instance._applicationName}");
+        }
+    }
+}

DotNetGuidePractice/HelloDotNetGuide/Program.cs

@@ -13,6 +13,12 @@ namespace HelloDotNetGuide
         {
             Console.WriteLine("欢迎来到DotNetGuide练习空间！！！");
 
+            #region ConstAndReadonlyExercise
+
+            //ConstAndReadonlyExercise.UpdateApplicationNameValue();
+
+            #endregion
+
             #region CSharp13GrammarExercise
 
             //CSharp13GrammarExercise.SpanDataPrintRun();

DotNetGuidePractice/HelloDotNetGuide/设计模式/单例模式.cs

@@ -41,10 +41,7 @@
                     {
                         lock (_lockObj)
                         {
-                            if (_instance == null)
-                            {
-                                _instance = new SingletonLazy();
-                            }
+                            _instance ??= new SingletonLazy();
                         }
                     }
                     return _instance;