1、new 运算符
new
关键字最常见的用途是创建一个类的实例。当使用 new 创建对象时,它为对象分配内存并调用构造函数来初始化该对象。例如,
StringBuilder str=new StringBuilder();
创建匿名类型:
var person = new { Name = "cjavapy", Age = 5 };
2、new 修饰符
在用作修饰符时,new 关键字可以显式隐藏从基类继承的成员。简单的说,就是现在写的这个类,想写一个和基类中相同的成员,而不继承基类的。运用多态的特性时,也不会调用这个显示隐藏的方法。具体看下如下代码:
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApp2 { public class Program { static void Main(string[] args) { animal a = new animal(); a.name = "animal"; a.say(); cat c = new cat(); c.name = "cat"; c.say(); dog d = new dog(); d.name = "dog"; d.say(); sheep s = new sheep(); s.name = "sheep"; s.say(); animal a1 = new cat(); a1.say(); animal a2 = new dog(); a2.say(); animal a3 = new sheep(); a3.say(); } } class animal { public string name { get; set; } public virtual void say() { Console.WriteLine("animal say"); } } class cat : animal { public override void say() { Console.WriteLine("cat say"); } } class dog : animal { public new void say() //这个方法被显示隐藏了 { Console.WriteLine("dog say"); } } class sheep : animal { } }
3、new 约束
用于在泛型声明中约束可能用作类型参数的参数的类型。举个例子看一下,泛型类中T要求有一个无参的构造函数,代码如下,
using System;
using System.Collections.Generic;
namespace ConsoleApplication2
{
public class Employee
{
private string name;
private int id;
public Employee()
{
name = "Temp";
id = 0;
}
public Employee(string s, int i)
{
name = s;
id = i;
}
public string Name
{
get { return name; }
set { name = value; }
}
public int ID
{
get { return id; }
set { id = value; }
}
}
class ItemFactory where T : new()
{
public T GetNewItem()
{
return new T();
}
}
public class Test
{
public static void Main()
{
ItemFactory EmployeeFactory = new ItemFactory(); ////此处编译器会检查Employee是否具有公有的无参构造函数。 //若没有则会有The Employee must have a public parameterless constructor 错误。 Console.WriteLine("{0}'ID is {1}.", EmployeeFactory.GetNewItem().Name, EmployeeFactory.GetNewItem().ID);
}
}
}