C# 0 The Complete Reference

alpha

 by code outside of 

MyClass

 is not allowed, methods defined within 

MyClass

 can freely access it, as the 

SetAlpha( )

 and 

GetAlpha( )

 methods show. The same 

is true for 

beta

.

The key point is this: A private member can be used freely by other members of its class, 

but it cannot be accessed by code outside its class.

Applying Public and Private Access

The proper use of public and private access is a key component of successful object-oriented 

programming. Although there are no hard and fast rules, here are some general principles 

that serve as guidelines:

•  Members of a class that are used only within the class itself should be private.

•  Instance data that must be within a specific range should be private, with access 

provided through public methods that can perform range checks.

•  If changing a member can cause an effect that extends beyond the member itself 

(that is, affects other aspects of the object), that member should be private, and 

access to it should be controlled.

•  Members that can cause harm to an object when improperly used should be private. 

Access to these members should be through public methods that prevent improper 

usage.

•  Methods that get and set the values of private data must be public.

•  Public instance variables are permissible when there is no reason for them to be 

private.

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Of course, there are many nuances that the preceding rules do not address, and special 

cases cause one or more rules to be violated. But, in general, if you follow these rules, you 

will be creating resilient objects that are not easily misused.