c# 中的静态关键字
static 是 C# 中的修饰符，适用于以下情况:
也适用于 属性 、事件、 操作符 。要创建一个静态成员(类、变量、方法、构造函数)，在它的声明前面加上关键字 static 。当一个成员被声明为静态时，可以用它的类名直接访问它。
静态类
借助 static 关键字声明一个静态类。静态类只能包含静态数据成员、静态方法和静态构造函数。不允许创建静态类的对象。静态类是 封 ，意味着一个静态类不能从另一个类继承。
例:
c
// C# program to illustrate the
// concept of a static class
using System;
// Creating static class
// Using static keyword
static class Tutorial {
// Static data members of Tutorial
public static string Topic = "Static class";
}
// Driver Class
public class GFG {
// Main Method
static public void Main()
{
// Accessing the static data members of Tutorial
Console.WriteLine("Topic name is : {0} ", Tutorial.Topic);
}
}
输出:
Topic name is : Static class
静态变量
静态变量是在 static 关键字的帮助下声明的。当一个变量被声明为静态变量时，就会创建该变量的一个副本，并在类级别的所有对象之间共享。静态变量是用类名来访问的，它们不需要任何对象来访问。
例:
c
// C# program to illustrate the
// concept of static variable
using System;
class Vehicle {
// Creating static variable
// Using static keyword
public static string Model_color = "Black";
}
// Driver Class
public class GFG {
// Main Method
static public void Main()
{
// Accessing the static variable
// using its class name
Console.WriteLine("Color of XY model is : {0} ",
Vehicle.Model_color);
}
}
输出:
Color of XY model is : Black
静态法
静态方法是借助 static 关键字声明的。静态方法是用类名访问的。静态方法可以访问静态和非静态字段，静态字段由静态方法直接访问，没有类名，而非静态字段需要对象。
例:
c
// C# program to illustrate the
// concept of static method
using System;
class Nparks {
static public int t = 104;
// Creating static method
// Using static keyword
public static void total()
{
Console.WriteLine("Total number of national parks"+
" present in India is :{0}", t);
}
}
// Driver Class
public class GFG {
// Main Method
static public void Main()
{
// Accessing the static method
// using its class name
Nparks.total();
}
}
输出:
Total number of national parks present in India is :104
静态构造函数
静态构造函数是在 static 关键字的帮助下声明的。静态构造函数在类中只能被调用一次，并且在创建对类中静态成员的第一个引用时被调用。静态构造函数是类的初始化静态字段或数据，只执行一次。
要记住的点:
- You can't scream directly.
- When it is executing, then the user has no control.
- Without access modifiers or any parameters.
- Automatically call the initialization class before creating the first instance.
例:
c
// C# Program to illustrate calling
// a Static constructor
using System;
class G1 {
// It is invoked before the first
// instance constructor is run.
static G1()
{
// The following statement produces
// the first line of output,
// and the line occurs only once.
Console.WriteLine("Example of Static Constructor");
}
// Instance constructor.
public G1(int j)
{
Console.WriteLine("Instance Constructor " + j);
}
// Instance method.
public string g1_detail(string name, string branch)
{
return "Name: " + name + " Branch: " + branch;
}
// Main Method
public static void Main()
{
// Here Both Static and instance
// constructors are invoked for
// first instance
G1 obj = new G1(1);
Console.WriteLine(obj.g1_detail("Sunil", "CSE"));
// Here only instance constructor
// will be invoked
G1 ob = new G1(2);
Console.WriteLine(ob.g1_detail("Sweta", "ECE"));
}
}
输出:
Example of Static Constructor
Instance Constructor 1
Name: Sunil Branch: CSE
Instance Constructor 2
Name: Sweta Branch: ECE
使用静态关键字的限制:
- Static keywords cannot be used by types other than indexer , finalizer or class.
- Static members are not referenced by instances.
- In C#, this is not allowed to refer to static methods or property accessors.
- In C#, if the static keyword is used with the class, the static class always contains static members.
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