Generic means the general size, not specific. In C#, generic means not specific khổng lồ a particular data type.

C# allows you to define generic classes, interfaces, abstract classes, fields,methods, static methods, properties, events, delegates, & operators using the type parameter & without the specific data type. A type parameter is a placeholder for a particular type specified when creating an instance of the generic type.

A generic type is declared by specifying a type parameter in an angle brackets after a type name, e.g. TypeName where T is a type parameter.

Generic Class

Generic classes are defined using a type parameter in an angle brackets after the class name. The following defines a generic class.


Example: Define Generic Class

class DataStoreT> public T Data get; set;
Above sầu, the DataStore is a generic class. T is called type parameter, which can be used as a type of fields, properties, method parameters, return types, & delegates in the DataStore class. For example, Data is generic property because we have used a type parameter T as its type instead of the specific data type.


cảnh báo
It is not required to use T as a type parameter. You can give any name khổng lồ a type parameter. Generally, T is used when there is only one type parameter. It is recommended to lớn use a more readable type parameter name as per requirement lượt thích TSession, TKey, TValue etc. Learn more about Type Parameter Naming Guidelines

You can also define multiple type parameters separated by a comma.


Example: Generic Class with Multiple Type Parameters

class KeyValuePairTKey, TValue> public TKey Key get; set; public TValue Value get; set;

Instantiating Generic Class

You can create an instance of generic classes by specifying an actual type in angle brackets. The following creates an instance of the generic class DataStore.

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DataStorestring> store = new DataStorestring>();
Above, we specified the string type in the angle brackets while creating an instance. So, T will be replaced with a string type wherever T is used in the entire class at compile-time. Therefore, the type of Data property would be a string.

The following figure illustrates how generics works.

*

You can assign a string value khổng lồ the Data property. Trying to lớn assign values other than string will result in a compile-time error.


DataStorestring> store = new DataStorestring>();store.Data = "Hello World!";//obj.Data = 123; //compile-time error
You can specify the different data types for different objects, as shown below.


Example: Generic class

DataStorestring> strStore = new DataStorestring>();strStore.Data = "Hello World!";//strStore.Data = 123; // compile-time errorDataStoreint> intStore = new DataStoreint>();intStore.Data = 100;//intStore.Data = "Hello World!"; // compile-time errorKeyValuePairint, string> kvp1 = new KeyValuePairint, string>();kvp1.Key = 100;kvp1.Value = "Hundred";KeyValuePairstring, string> kvp2 = new KeyValuePairstring, string>();kvp2.Key = "IT";kvp2.Value = "Information Technology";
Try it
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Generic Class Characteristics

A generic class increases the reusability. The more type parameters mean more reusable it becomes. However, too much generalization makes code difficult to understand and maintain. A generic class can be a base class to other generic or non-generic classes or abstract classes. A generic class can be derived from other generic or non-generic interfaces, classes, or abstract classes.

Generic Fields

A generic class can include generic fields. However, it cannot be initialized.


Example: Generic Field

class DataStore public T data;
The following declares a generic array.

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Example: Generic Array

class DataStoreT> public T<> data = new T<10>;

Generic Methods

A method declared with the type parameters for its return type or parameters is called a generic method.


Example: Generic Methods

class DataStore{ private T<> _data = new T<10>; public void AddOrUpdate(int index, T item) if(index >= 0 &và index public T GetData(int index) if(index >= 0 && index return _data; else return default(T);
Above, the AddorUpdate() & the GetData() methods are generic methods. The actual data type of the thành phầm parameter will be specified at the time of instantiating the DataStore class, as shown below.


Example: Generic Methods

DataStorestring> cities = new DataStorestring>();cities.AddOrUpdate(0, "Mumbai");cities.AddOrUpdate(1, "Chicago");cities.AddOrUpdate(2, "London");DataStoreint> empIds = new DataStoreint>();empIds.AddOrUpdate(0, 50);empIds.AddOrUpdate(1, 65);empIds.AddOrUpdate(2, 89);
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The generic parameter type can be used with multiple parameters with or without non-generic parameters và return type. The followings are valid generic method overloading.


Example: Generic Method Overloading

public void AddOrUpdate(int index, T data) public void AddOrUpdate(T data1, T data2) public void AddOrUpdate(T data1, U data2) public void AddOrUpdate(T data)
A non-generic class can include generic methods by specifying a type parameter in angle brackets with the method name, as shown below.

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Example: Generic Method in Non-generic Class

class Printer public void Print(T data) Console.WriteLine(data); Printer printer = new Printer();printer.Printint>(100);printer.Print(200); // type infer from the specified valueprinter.Printstring>("Hello");printer.Print("World!"); // type infer from the specified value
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Advantages of Generics

Generics increase the reusability of the code. You don"t need to lớn write code to lớn handle different data types. Generics are type-safe. You get compile-time errors if you try lớn use a different data type than the one specified in the definition. Generic has a performance advantage because it removes the possibilities of boxing và unboxing.
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