Apache web server for windows - CHAPTER 3 C# LANGUAGE FUNDAMENTALS 77 Table
CHAPTER 3 C# LANGUAGE FUNDAMENTALS 77 Table 3-4. C# Accessibility Keywords C# Access Modifier Meaning in Life public Marks amember as accessible from an object variable as well as any derived classes. private Marks a method as accessible only by the class that has defined the method. In C#, all members are private by default. protected Marks a method as usable by the defining class, as well as any derived classes. Protected methods, however, are not accessible from an object variable. internal Defines a method that is accessible by any type in the same assembly, but not outside the assembly. protected internal Defines a method whose access is limited to the current assembly or types derived from the defining class in the current assembly. As you may already know, members that are declared public are directly accessible from an object reference via the dot operator (.). Private members cannot be accessed by an object reference, but instead are called internally by the object to help the instance get its work done (i.e., private helper functions). Protected members are only truly useful when you create class hierarchies, which is the subject of Chapter 4. As far as internal or internal protected members are concerned, they are only truly useful when you are creating .NET code libraries (such as a managed *.dll, a topic examined in Chapter 11). To illustrate the implications of these keywords, assume you have created a class (SomeClass) using each of the possible member access modifiers: // Member visibility options. class SomeClass { // Accessible anywhere. public void PublicMethod(){} // Accessible only from SomeClass types. private void PrivateMethod(){} // Accessible from SomeClass and any descendent. protected void ProtectedMethod(){} // Accessible from within the same assembly. internal void InternalMethod(){} // Assembly-protected access. protected internal void ProtectedInternalMethod(){} // Unmarked members are private by default in C#. void SomeMethod(){} } Now assume you have created an instance of SomeClass and attempt to invoke each method using the dot operator: static void Main(string[] args) { // Make an object and attempt to call members. SomeClass c = new SomeClass(); c.PublicMethod();
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