类是用户定义的蓝图或原型，从中可以创建对象。基本上，一个类将字段和方法(定义动作的成员函数)组合到一个单元中。在C＃中，允许用户在另一个类中定义一个类。这种类型的类称为嵌套类。此功能使用户可以对仅在一个地方使用的类进行逻辑分组，从而增加了封装的使用，并创建了更具可读性和可维护性的代码。
句法：
class Outer_class {
// Code..
class Inner_class {
// Code..
}
}
例子：
// C# program to illustrate the
// concept of nested class
using System;
// Outer class
public class Outer_class {
// Method of outer class
public void method1()
{
Console.WriteLine("Outer class method");
}
// Inner class
public class Inner_class {
// Method of inner class
public void method2()
{
Console.WriteLine("Inner class Method");
}
}
}
// Driver Class
public class GFG {
// Main method
static public void Main()
{
// Create the instance of outer class
Outer_class obj1 = new Outer_class();
obj1.method1();
// This statement gives an error because
// you are not allowed to access inner
// class methods with outer class objects
// obj1. method2();
// Creating an instance of inner class
Outer_class.Inner_class obj2 =
new Outer_class.Inner_class();
// Accessing the method of inner class
obj2.method2();
}
}
输出：
Outer class method
Inner class Method
要点：
- 可以将嵌套类声明为private，public，protected，internal，protected internal或private protected 。
- 如上例所示，不允许外部类直接访问内部类成员。
- 您可以在外部类中创建内部类的对象。
- 内部类可以访问外部类中声明的静态成员，如下例所示：
例子：
// C# program to illustrate the // concept of nested class accessing // static members of the outer class using System; // Outer class public class Outer_class { // Static data member of the outer class public static string str = "Geeksforgeeks"; // Inner class public class Inner_class { // Static method of Inner class public static void method1() { // Displaying the value of a // static member of the outer class Console.WriteLine(Outer_class.str); } } } // Driver Class public class GFG { // Main method static public void Main() { // Accessing static method1 // of the inner class Outer_class.Inner_class.method1(); } }输出 ：
Geeksforgeeks - 内部类可以访问外部类中声明的非静态成员，如以下示例所示：
例子：
// C# program to illustrate the // concept of nested class // accessing non-static member // of the outer class using System; // Outer class public class Outer_class { // Non-static data // member of outer class public int number = 1000000; // Inner class public class Inner_class { // Static method of Inner class public static void method1() { // Creating the object of the outer class Outer_class obj = new Outer_class(); // Displaying the value of a // static member of the outer class // with the help of obj Console.WriteLine(obj.number); } } } // Driver Class public class GFG { // Main method static public void Main() { // Accessing static method1 // of inner class Outer_class.Inner_class.method1(); } }输出 ：
1000000 - 实例内部类可以访问在外部类中声明的非静态成员，如以下示例所示：
例子：
// C# program to illustrate the // concept of nested class // accessing non-static member // of the outer class using System; // Outer class public class Outer_class { // Non-static data // member of outer class public int number = 2000000; // Non-static reference to Inner_class // instance. public Inner_class Inner { get; set; } // Constructor to establish link between // instance of Outer_class to its // instance of the Inner_class public Outer_class() { this.Inner = new Inner_class(this); } // Inner class private class Inner_class { // private field to hold // reference to an instance // of the Outer_class private Outer_class obj; // constructor that establishes // a reference to the Outer_class // to use within an Inner_cass instance public Inner_class(Outer_class outer) { obj = outer; } // Method of Inner class public void method1() { // Displaying the value of a // member of the outer class // with the help of obj Console.WriteLine(obj.number); } } } // Driver Class public class GFG { // Main method public void Main() { // Create instance of Outer_class Outer_class Outer = new Outer_class(); // Accessing static method1 // of inner class Outer.Inner.method1(); } }输出 ：
2000000 - 嵌套类的范围受其封闭类的范围限制。
- 默认情况下，嵌套类是私有的。
- 在C＃中，允许用户将一个类(包括嵌套类)继承到另一个类中。
例子：
// C# program to illustrate the // concept inheritance using System; // Outer class public class Outer_class { // Method of outer class public void method1() { Console.WriteLine("Outer class method"); } // Inner class public class Inner_class { } } // Derived class public class Exclass : Outer_class { // Method of derived class public void func() { Console.WriteLine("Method of derived class"); } } // Driver Class public class GFG { // Main method static public void Main() { // Creating object of // the derived class Exclass obj = new Exclass(); obj.func(); obj.method1(); } }输出 ：
Method of derived class Outer class method - 在C＃中，允许用户从外部类继承嵌套类。