May 11, 2021 C#
Generic allows you to delay writing specifications for the data types of programming elements in a class or method until it is actually used in a program. In other words, generics allow you to write a class or method that can work with any data type.
You can write specifications for classes or methods from alternative parameters for data types. W hen the compiler encounters a function call from a class's constructor or method, it generates code to handle the specified data type. This simple example will help you understand the concept:
using System;
using System.Collections.Generic;
namespace GenericApplication
{
public class MyGenericArray<T>
{
private T[] array;
public MyGenericArray(int size)
{
array = new T[size + 1];
}
public T getItem(int index)
{
return array[index];
}
public void setItem(int index, T value)
{
array[index] = value;
}
}
class Tester
{
static void Main(string[] args)
{
// 声明一个整型数组
MyGenericArray<int> intArray = new MyGenericArray<int>(5);
// 设置值
for (int c = 0; c < 5; c++)
{
intArray.setItem(c, c * 5);
} // 获取值
for (int c = 0; c < 5; c++)
{
Console.Write(intArray.getItem(c) + " ");
}
Console.WriteLine(); // 声明一个字符数组
MyGenericArray<char> charArray = new MyGenericArray<char>(5);
// 设置值
for (int c = 0; c < 5; c++)
{
charArray.setItem(c, (char)(c + 97));
} // 获取值
for (int c = 0; c < 5; c++)
{
Console.Write(charArray.getItem(c) + " ");
}
Console.WriteLine();
Console.ReadKey();
}
}
}
When the above code is compiled and executed, it produces the following results:
0 5 10 15 20
a b c d e
Using generics is a technique for enhancing program functionality in the following ways:
In the example above, we've already used generic classes, and we can declare generic methods with type parameters. The following procedure illustrates this concept:
using System;
using System.Collections.Generic;
namespace GenericMethodAppl
{
class Program
{
static void Swap<T>(ref T lhs, ref T rhs)
{
T temp;
temp = lhs;
lhs = rhs;
rhs = temp;
}
static void Main(string[] args)
{
int a, b;
char c, d;
a = 10;
b = 20;
c = 'I';
d = 'V';
// 在交换之前显示值
Console.WriteLine("Int values before calling swap:");
Console.WriteLine("a = {0}, b = {1}", a, b);
Console.WriteLine("Char values before calling swap:");
Console.WriteLine("c = {0}, d = {1}", c, d);
// 调用 swap
Swap<int>(ref a, ref b);
Swap<char>(ref c, ref d);
// 在交换之后显示值
Console.WriteLine("Int values after calling swap:");
Console.WriteLine("a = {0}, b = {1}", a, b);
Console.WriteLine("Char values after calling swap:");
Console.WriteLine("c = {0}, d = {1}", c, d);
Console.ReadKey();
}
}
}
When the above code is compiled and executed, it produces the following results:
Int values before calling swap:
a = 10, b = 20
Char values before calling swap:
c = I, d = V
Int values after calling swap:
a = 20, b = 10
Char values after calling swap:
c = V, d = I
You can define generic delegates from type parameters. For example:
delegate T NumberChanger<T>(T n);
The following example demonstrates the use of delegates:
using System;
using System.Collections.Generic;
delegate T NumberChanger<T>(T n);
namespace GenericDelegateAppl
{
class TestDelegate
{
static int num = 10;
public static int AddNum(int p)
{
num += p;
return num;
}
public static int MultNum(int q)
{
num *= q;
return num;
}
public static int getNum()
{
return num;
}
static void Main(string[] args)
{
// 创建委托实例
NumberChanger<int> nc1 = new NumberChanger<int>(AddNum);
NumberChanger<int> nc2 = new NumberChanger<int>(MultNum);
// 使用委托对象调用方法
nc1(25);
Console.WriteLine("Value of Num: {0}", getNum());
nc2(5);
Console.WriteLine("Value of Num: {0}", getNum());
Console.ReadKey();
}
}
}
When the above code is compiled and executed, it produces the following results:
Value of Num: 35
Value of Num: 175