Beginner Topic: Centralizing Initialization in C#

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Beginner Topic: Centralizing Initialization
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Notice that in the Employee(int id) constructor implementation from Listing 520, you cannot call this(firstName, LastName) because no such parameters exist on this constructor To enable such a pattern in which all initialization code happens through one method you must create a separate method, as shown in Listing 521
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Listing 521 Providing an Initialization Method
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class Employee { public Employee( string firstName, string lastName) { int id; // Generate an employee ID // Initialize(id, firstName, lastName); } public Employee(int id, string firstName, string lastName ) { Initialize(id, firstName, lastName); } public Employee(int id) { string firstName; string lastName; Id = id; // Look up employee data // Initialize(id, firstName, lastName); } private void Initialize( int id, string firstName, string lastName) { Id = id; FirstName = firstName; LastName = lastName; } // }
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In this case, the method is called Initialize() and it takes both the names and the employee IDs Note that you can continue to call one constructor from another, as you do with Employee(string firstName, string lastName)
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Static
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The HelloWorld example in 1 first presented the keyword static; however, it did not define it fully This section defines the static keyword fully
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Unlike many of the languages that came before it, C# does not have global variables or global functions All fields and methods in C# appear within the context of a class The equivalent of a global field or function within the realm of C# is a static field or function There is no functional difference between global variables/functions and C# static fields/methods, except that static fields/functions can include access modifiers, such as private, that can limit the access and provide better encapsulation
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To begin, consider an example Assume that the employee Id value needs to be unique for each employee One way to accomplish this is to store a counter to track each employee ID If the value is stored as an instance field, however, every time you instantiate an object, a new NextId field will be created such that every instance of the Employee object would consume memory for that field The biggest problem is that each time an Employee object instantiated, the NextId value on all of the previously instantiated Employee objects would need to be updated with the next ID value What you need is a single field that all Employee object instances share
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Static Fields
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To define data that is available across multiple instances, you use the static keyword, as demonstrated in Listing 522
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Listing 522 Declaring a Static Field
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class Employee { public Employee(string firstName, string lastName) { FirstName = firstName; LastName = lastName; Id = NextId; NextId++; } // public public public public public // } static int NextId; int Id; string FirstName; string LastName; string Salary;
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In this example, the NextId field declaration includes the static modifier and therefore is called a static field Unlike Id, a single storage location for NextId is shared across all instances of Employee Inside the Employee constructor, you assign the new Employee object's Id the value of NextId immediately before incrementing it When another Employee class is created, NextId will be incremented and the new Employee object's Id field will hold a different value Just as instance fields (nonstatic fields) can be initialized at declaration time, so can static fields, as demonstrated in Listing 523
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Listing 523 Assigning a Static Field at Declaration
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class Employee { // public static int NextId = 42; // }
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If no initialization for a static field is provided, the static field will automatically be assigned its default value ( 0, null, false, and so on), and it will be possible to access the static field even if it has never been explicitly assigned Nonstatic fields, or instance fields, have a new value for each object to which they belong In contrast, static fields don't belong to the instance, but rather, to the class itself As a result, you access a static field from outside a class via the class name Consider the new Program class shown in Listing 524
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