However, once we make the member variables private, we can no longer initialize classes in this way. This makes sense: if you can`t access a variable directly (because it`s private), you shouldn`t be able to initialize it directly. The difference between a class and an object is the same as the difference between the concept of a dog and the particular dog sitting at your feet as you read this. You can`t play fetch with the definition of a dog, only with an instance. Helping initialize the value for class objects is simple, consistent, and can help you spot errors, especially as you learn. If you do not specify a specific initializer, the constructor initializes each integer member variable to zero (0). However, in the case shown, the second member initializes with 30: When you declare a new class, you define the properties of all objects in that class and their behavior. For example, if you`re creating a window environment, you can create screen widgets (more commonly known as controls in Windows programming) to make it easier for users to interact with your app. An interesting control could be a list box, which is very useful for displaying a list of choices to the user and allowing them to choose from the list.

As always, we prefer list initialization. We will find the reasons (templates and std::initializer_list) to use direct initialization when calling constructors later in the tutorials. There is another special constructor that could do something different when initializing parentheses, in this case we must use direct initialization. We will talk about these manufacturers later. The goal of this exercise is to write a class definition that includes a variety of methods, including constructors, modifiers, and pure functions. It is not legal to explicitly name a destroyer. Your destroyer is called by the garbage collector. If you manage valuable unmanaged resources (such as file handles) that you want to close and delete as soon as possible, you should implement the IDisposable interface.

[6] (For more information on interfaces, see Chapter 8.) The IDisposable interface requires its implementers to define a method called Dispose() to perform the cleanup that you deem crucial. The most common example is that of more than one manufacturer. In the examples shown so far, the constructor has used only one parameter: a DateTime object. It would be convenient to be able to define new Time objects at any time by passing values for year, month, date, hour, minute, and second. It would be even more convenient if some customers could use one builder and other customers could use the other builder. Function overload provides exactly these eventualities. C# applies a specific assignment that requires that a value be assigned to all variables before they are used. In example 4-7, if you do not initialize theHour, theMinute, and theSecond before passing them as parameters to GetTime(), the compiler complains. However, initialization simply sets its values to 0 before passing them to the method: this class is designed to contain a fractional value as an integer numerator and denominator.

We defined a default constructor called Fraction (identical to the class). In C#, it is not legal to access a static method or member variable through an instance, and trying to do so generates a compiler error (note from C++ programmers). For example, you can add the following static constructor to the Time class shown in Example 4-4: The .NET Framework defines an IClone interface to support the copy constructor concept. (Interfaces are discussed in detail in Chapter 8.) This interface defines a single method: Clone( ). Classes that support the idea of a Copy constructor must implement ICloneable and then implement a flat copy (calling MemberwiseClone) or a deep copy (for example, by calling the copy constructor and manually copying all members). The signature of a method is defined by its name and parameter list. Two methods differ in their signatures if they have different names or lists of different parameters. Parameter lists can be distinguished by different numbers or types of parameters.

For example, in the following code, the first method differs from the second method in the number of parameters and the second from the third method in the parameter types: The SomeMethod( ) method takes int and float and displays them with Console.WriteLine( ). The firstParam and secondParam parameters are treated as local variables in SomeMethod(). The default values of the constructors work in the same way as for all other functions, so in the above case, where we call six{6}, the function Fraction(int, int) is called, the second parameter being set to 1 by default. The printPerson method contains a line of code that uses the name and age instance variables: the class diagram says nothing about its internal implementations. Instance variables are referenced with the prefix this. All variables in the object are visible and available in the method. Many new programmers don`t know if the constructors create the objects or not. This is not the case: the compiler configures the memory allocation for the object before the constructor is called. In addition to the class name, instance variables, and constructor, the class diagram now includes the printPerson method. Because the method is supplied with the public modifier, the method name is preceded by a plus sign.

No parameters are defined for the method, so nothing is enclosed in parentheses of the method. The method is also tagged with information indicating that it does not return a value, in this case null. If the programmer does not define a constructor for a class, Java automatically creates a default constructor for the class. A default constructor is a constructor that does nothing but create the object. Object variables do not remain initialized (typically, the value of all object references is zero, which means they do not refer to anything, and the values of primitives are 0) The Cat class has been reduced to the essentials. A static member variable named instances is created and initialized to 0. Note that the static member is considered part of the class, not a member of an instance, and therefore cannot be initialized by the compiler when creating an instance. Therefore, if you want to initialize a static member, you must provide an explicit initializer. When additional instances of Cats are created (in a constructor), the number is increased.

Examine the highlighted line in Main() where the DateTime object is created by calling the static Now property. Now creates a DateTime value, which in this case is copied to the stack`s currentTime variable. We want to mark static values as constant, but this is not possible because we do not initialize them until the static constructor runs. C# provides the read-only keyword for exactly this purpose. If you modify the declarations of class member variables as follows: This chapter describes the features of the C# language that are used to specify new classes. The elements of a class, that is, its behavior and properties, are collectively called its members. This chapter shows how to use methods to define class behavior and how to maintain class state in member variables (often called fields). Additionally, this chapter introduces properties that behave like methods for the class developer, but resemble fields for the class`s clients. First, consider a few things that aren`t algorithms. When you learned how to multiply single-digit numbers, you probably memorized the multiplication table. In fact, you`ve memorized 100 specific solutions, so the knowledge isn`t really algorithmic.