в 15:31, 26 мая 2010

2010-05-26T15:31:53Z

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2010-05-26T12:16:04Z

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==A base class reference can refer to a derived class object==

<source lang="csharp">using System;

class BaseClass {
public int a;

public BaseClass(int i) {
a = i;
}
}

class DerivedClass : BaseClass {
public int b;

public DerivedClass(int i, int j) : base(j) {
b = i;
}
}

class MainClass {
public static void Main() {
BaseClass x = new BaseClass(10);
BaseClass x2;
DerivedClass y = new DerivedClass(5, 6);

x2 = x; // OK, both of same type
Console.WriteLine("x2.a: " + x2.a);

x2 = y; // Ok because DerivedClass is derived from BaseClass
Console.WriteLine("x2.a: " + x2.a);

// BaseClass references know only about BaseClass members
x2.a = 19; // OK
// x2.b = 27; // Error, BaseClass doesn"t have a b member
}
}</source>
<pre class=codeResult>x2.a: 10
x2.a: 6</pre>

==Illustrates member accessibility in subclass==

<source lang="csharp">using System;
public class Car
{
private string make;
protected string model;
public Car(string make, string model)
{
this.make = make;
this.model = model;
}
public virtual void Start()
{
startCar();
System.Console.WriteLine("Vehicle started");
}
private void startCar()
{
System.Console.WriteLine("Turning starter motor...");
}
}
public class MyFirstCar : Car
{
public MyFirstCar(string make, string model) : base(make, model)
{
}
public override void Start()
{
Console.WriteLine("Starting " + model);
base.Start();
}
}
class MainClass
{
public static void Main()
{
MyFirstCar myCar = new MyFirstCar("Toyota", "MR2");
myCar.Start();
}
}</source>
<pre class=codeResult>Starting MR2
Turning starter motor...
Vehicle started</pre>

==Illustrates member hiding==

<source lang="csharp">using System;
public class BaseClass
{
public string lastName;
public string firstName;
public BaseClass(string lastName, string firstName)
{
Console.WriteLine("In BaseClass constructor");
this.lastName = lastName;
this.firstName = firstName;
Console.WriteLine("this.lastName = " + this.lastName);
Console.WriteLine("this.firstName = " + this.firstName);
}
public void DisplayfirstName()
{
Console.WriteLine("In BaseClass DisplayfirstName() method");
Console.WriteLine("firstName = " + firstName);
}
}
public class DerivedClass : BaseClass
{
public new string firstName;
public DerivedClass(string lastName, string firstName) : base(lastName, "Test")
{
Console.WriteLine("In DerivedClass constructor");
this.firstName = firstName;
Console.WriteLine("this.firstName = " + this.firstName);
}
public new void DisplayfirstName()
{
Console.WriteLine("In DerivedClass DisplayfirstName() method");
Console.WriteLine("firstName = " + firstName);
base.DisplayfirstName();
}
}

class MainClass
{
public static void Main()
{
Console.WriteLine("Creating a DerivedClass object");
DerivedClass myDerivedClass = new DerivedClass("A", "B");
Console.WriteLine("Back in Main() method");
Console.WriteLine("myDerivedClass.lastName = " + myDerivedClass.lastName);
Console.WriteLine("myDerivedClass.firstName = " + myDerivedClass.firstName);
Console.WriteLine("Calling myDerivedClass.DisplayfirstName()");
myDerivedClass.DisplayfirstName();
}
}</source>
<pre class=codeResult>Creating a DerivedClass object
In BaseClass constructor
this.lastName = A
this.firstName = Test
In DerivedClass constructor
this.firstName = B
Back in Main() method
myDerivedClass.lastName = A
myDerivedClass.firstName = B
Calling myDerivedClass.DisplayfirstName()
In DerivedClass DisplayfirstName() method
firstName = B
In BaseClass DisplayfirstName() method
firstName = Test</pre>

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Csharp/CSharp Tutorial/Class/Derived Class - История изменений

в 15:31, 26 мая 2010

Admin: 1 версия