Public Method in VS .NET

Create QR Code in VS .NET Public Method

In addition, types that derive from System.Object have access to the protected methods listed in Table 4-2 .

TABLE 4-2

This nonvirtual method creates a new instance of the type and sets the new object s instance fields to be identical to the this object s instance fields . A reference to the new instance is returned . This virtual method is called when the garbage collector determines that the object is garbage before the memory for the object is reclaimed . Types that require cleanup when collected should override this method . I ll talk about this important method in much more detail in 21, Automatic Memory Management (Garbage Collection) .

The CLR requires all objects to be created using the new operator . The following line shows how to create an Employee object:

Employee e = new Employee("ConstructorParam1");

Here s what the new operator does: 1. It calculates the number of bytes required by all instance fields defined in the type and all of its base types up to and including System.Object (which defines no instance fields of its own) . Every object on the heap requires some additional members called the type object pointer and the sync block index used by the CLR to manage the object . The bytes for these additional members are added to the size of the object . 2. It allocates memory for the object by allocating the number of bytes required for the specified type from the managed heap; all of these bytes are then set to zero (0) . 3. It initializes the object s type object pointer and sync block index members . 4. The type s instance constructor is called, passing it any arguments (the string "ConstructorParam1" in the preceding example) specified in the call to new . Most compilers automatically emit code in a constructor to call a base class s constructor . Each constructor is responsible for initializing the instance fields defined by the type whose constructor is being called . Eventually, System.Object s constructor is called, and this constructor method does nothing but return . You can verify this by using ILDasm .exe to load MSCorLib .dll and examine System.Object s constructor method . After new has performed all of these operations, it returns a reference (or pointer) to the newly created object . In the preceding code example, this reference is saved in the variable e, which is of type Employee . By the way, the new operator has no complementary delete operator; that is, there is no way to explicitly free the memory allocated for an object . The CLR uses a garbage-collected environment (described in 21) that automatically detects when objects are no longer being used or accessed and frees the object s memory automatically .

One of the most important features of the CLR is type safety . At runtime, the CLR always knows what type an object is . You can always discover an object s exact type by calling the GetType method . Because this method is nonvirtual, it is impossible for a type to spoof another type . For example, the Employee type can t override the GetType method and have it return a type of SuperHero . Developers frequently find it necessary to cast an object to various types . The CLR allows you to cast an object to its type or to any of its base types . Your choice of programming language dictates how to expose casting operations to the developer . For example, C# doesn t require any special syntax to cast an object to any of its base types, because casts to base types are considered safe implicit conversions . However, C# does require the developer to explicitly cast an object to any of its derived types since such a cast could fail at runtime . The following code demonstrates casting to base and derived types: