Csharp/C Sharp/Class Interface/Object Cast
Содержание
Casting Objects
<source lang="csharp"> using System; public class MotorVehicle {
public string model;
public MotorVehicle(string model) {
this.model = model;
}
public void Start() {
Console.WriteLine(model + " started");
}
} public class Product : MotorVehicle {
public bool convertible;
public Product(string model, bool convertible) :
base(model) {
this.convertible = convertible;
}
}
public class Motorcycle : MotorVehicle {
public bool sidecar;
public Motorcycle(string model, bool sidecar) :
base(model) {
this.sidecar = sidecar;
}
public void PullWheelie() {
Console.WriteLine(model + " pulling a wheelie!");
}
} class MainClass {
public static void Main() {
Product myProduct = new Product("MR2", true);
MotorVehicle myMotorVehicle = (MotorVehicle)myProduct;
Console.WriteLine("myMotorVehicle.model = " + myMotorVehicle.model);
myMotorVehicle.Start();
Motorcycle myMotorcycle = new Motorcycle("V-Rod", true);
MotorVehicle myMotorVehicle2 = (MotorVehicle)myMotorcycle;
Console.WriteLine("myMotorVehicle2.model =" + myMotorVehicle2.model);
myMotorVehicle2.Start();
Motorcycle myMotorcycle2 = (Motorcycle)myMotorVehicle2;
Console.WriteLine("myMotorcycle2.model = " + myMotorcycle2.model);
Console.WriteLine("myMotorcycle2.sidecar = " + myMotorcycle2.sidecar);
myMotorcycle2.Start();
myMotorcycle2.PullWheelie();
}
}
</source>
Casting objects: downcast
<source lang="csharp"> using System;
public class CPU {
public string model;
public CPU(string model) {
this.model = model;
}
public void Start() {
Console.WriteLine(model + " started");
}
}
public class Intel : CPU {
public bool convertible;
public Intel(string model, bool convertible) : base(model) {
this.convertible = convertible;
}
}
public class AMD : CPU {
public bool sidecar;
public AMD(string model, bool sidecar) : base(model) {
this.sidecar = sidecar;
}
public void PullWheelie() {
Console.WriteLine(model + " pulling a wheelie!");
}
}
class Test {
public static void Main() {
Intel myIntel = new Intel("MR2", true);
// create a AMD object
AMD myAMD = new AMD("V-Rod", true);
// cast myAMD to CPU (upcast)
CPU myCPU2 = (CPU) myAMD;
// cast myCPU2 to AMD (downcast)
AMD myAMD2 = (AMD) myCPU2;
// myMotorCycle2 has access to all members of the AMD class
Console.WriteLine("myAMD2.model = " + myAMD2.model);
Console.WriteLine("myAMD2.sidecar = " + myAMD2.sidecar);
myAMD2.Start();
myAMD2.PullWheelie();
}
}
</source>
Casting objects: upcast
<source lang="csharp"> using System;
public class CPU {
public string model;
public CPU(string model) {
this.model = model;
}
public void Start() {
Console.WriteLine(model + " started");
}
}
public class Intel : CPU {
public bool convertible;
public Intel(string model, bool convertible) : base(model) {
this.convertible = convertible;
}
}
public class AMD : CPU {
public bool sidecar;
public AMD(string model, bool sidecar) : base(model) {
this.sidecar = sidecar;
}
public void PullWheelie() {
Console.WriteLine(model + " pulling a wheelie!");
}
}
class Test {
public static void Main() {
Intel myIntel = new Intel("MR2", true);
// cast myIntel to CPU (upcast)
CPU myCPU = (CPU) myIntel;
Console.WriteLine("myCPU.model = " + myCPU.model);
myCPU.Start();
}
}
</source>
Downcast will fail.
<source lang="csharp"> class Employee { }
class ContractEmployee : Employee { }
class CastExample3 {
public static void Main ()
{
ContractEmployee ce = (ContractEmployee)new Employee();
}
}
</source>
This code raises an exception at run time because of an invalid cast
<source lang="csharp"> using System;
public class Starter {
public static void Main() {
MyClass obj = new MyClass();
// Fails at compile time
// YClass alias=obj;
// Fails at run time
YClass alias = (YClass)obj;
obj.MethodA();
obj.MethodB();
}
} public class MyClass {
public virtual void MethodA() {
}
public virtual void MethodB() {
}
} public class YClass : MyClass {
public override void MethodA() {
}
}
</source>
