In my C# application i have a base class, which contains a function Myfunction.
I have a derived class from the above base class which also contains the same function as in base class, is this concept is correct implementation?
public class BaseClass
{
public void MyFunction()
{
Console.WriteLine("");
}
}
public class DerivedClass:BaseClass
{
public void MyFunction()
{
Console.WriteLine("");
}
}
i am a newbee in Programing , sorry for my english
You've actually hidden BaseClass.MyFunction by doing it that way.
If you want to override properly, you must declare the base version as virtual (or abstract) and then specify override:
public class BaseClass
{
public virtual void MyFunction() { }
}
public class DerivedClass:BaseClass
{
public override void MyFunction() { }
}
Overloading and overriding are different things. The above shows overriding. Overloading refers to when there are multiple methods with the same name, but different parameters. E.g. if you have these methods:
public void MyFunction(int i) {}
public void MyFunction(decimal d) {}
You would say that there are two overloads of MyFunction.
No, this is wrong implementation for method overloading.
If you create a method with same name, and same parameters then it will be method overriding.
If you create a method with same name, but different parameters then it will be method overloading.
If you need to implement your example for method overriding, then add a override keyword on your derived class method and add a virtual keyword with your base class method:
public class BaseClass
{
public virtual void MyFunction()
{
Console.WriteLine("");
}
}
public class DerivedClass:BaseClass
{
public override void MyFunction()
{
Console.WriteLine("");
}
}
If you want to implement an example of overloading, then you will just have to change the parameters of your both methods. Change means they must be different from each other. e.g. :
public class BaseClass
{
public void MyFunction()
{
Console.WriteLine("");
}
}
public class DerivedClass:BaseClass
{
public void MyFunction(string input)
{
Console.WriteLine("");
}
}
In this example, MyFunction in DerivedClass overrides MyFunction in BaseClass.
If you had another MyFunction, this time 'MyFunction(int parameter)', you would have overloaded MyFunction.
You must overload/overrieds methods in this way
public class derived_Class : mybaseclass
{
public override void mymethod()
{
// IF you want to call the base class function as well then you call base.mymethod() ;
base.mymethod();
}
}
class mybaseclass
{
// When you want to overide a method , you must use Virtual keyword
public virtual void mymethod()
{
}
// This is an overload of overload_method
// when you write many methods from same name with different arguments, it's an overload of the method
public void overload_method()
{
}
public void overload_method(string m)
{
}
// When you use an overload
public void use()
{
overload_method();
overload_method(null);
}
}
Related
I have a base class and a class inheriting base. The base class has several virtual functions that the inherited class may override. However, the virtual functions in the base class has code that MUST to run before the inherited class overrides get called. Is there some way that I can call the base classes virtual functions first then the inherited class overrides. Without making a call to base.function().
I know I can simply make two functions, one that gets called, the other virtual. But is there a way I can keep the same names as well? I know I may need to change some things around.
class myBase
{
public virtual myFunction()
{ /* must-run code, Called first */ }
}
class myInherited : myBase
{
public override myFunction()
{ /* don't use base.myFunction();,
called from base.myFunction(); */ }
}
Similar question here.
C# doesn't have support for automatically enforcing this, but
you can enforce it by using the template method pattern. For example, imagine you had this code:
abstract class Animal
{
public virtual void Speak()
{
Console.WriteLine("I'm an animal.");
}
}
class Dog : Animal
{
public override void Speak()
{
base.Speak();
Console.WriteLine("I'm a dog.");
}
}
The trouble here is that any class inheriting from Animal needs to call base.Speak(); to ensure the base behavior is executed. You can automatically enforce this by taking the following (slightly different) approach:
abstract class Animal
{
public void Speak()
{
Console.WriteLine("I'm an animal.");
DoSpeak();
}
protected abstract void DoSpeak();
}
class Dog : Animal
{
protected override void DoSpeak()
{
Console.WriteLine("I'm a dog.");
}
}
In this case, clients still only see the polymorphic Speak method, but the Animal.Speak behavior is guaranteed to execute. The problem is that if you have further inheritance (e.g. class Dachshund : Dog), you have to create yet another abstract method if you want Dog.Speak to be guaranteed to execute.
A common solution that can be found in the .NET Framework is to split a method in a public method XXX and a protected, virtual method OnXXX that is called by the public method. For your example, it would look like this:
class MyBase
{
public void MyMethod()
{
// do something
OnMyMethod();
// do something
}
protected virtual void OnMyMethod()
{
}
}
and
class MyInherited : MyBase
{
protected override void OnMyMethod()
{
// do something
}
}
public abstract class BaseTemp
{
public void printBase() {
Console.WriteLine("base");
print();
}
public abstract void print();
}
public class TempA: BaseTemp
{
public override void print()
{
Console.WriteLine("TempA");
}
}
public class TempB: BaseTemp
{
public override void print()
{
Console.WriteLine("TempB");
}
}
There is no way to do what you're seeking other than the 2 ways you already named.
Either you make 2 functions in the base class, one that gets called and the other virtual.
Or you call base.functionName in the sub-class.
Not exactly. But I've done something similar using abstract methods.
Abstract methods must be overriden by derived classes. Abstract procs are virtual so you can be sure that when the base class calls them the derived class's version is called. Then have your base class's "Must Run Code" call the abstract proc after running. voila, your base class's code always runs first (make sure the base class proc is no longer virtual) followed by your derived class's code.
class myBase
{
public /* virtual */ myFunction() // remove virtual as we always want base class's function called here
{ /* must-run code, Called first */
// call derived object's code
myDerivedMustcallFunction();
}
public abstract myDerivedMustCallFunction() { /* abstract functions are blank */ }
}
class myInherited : myBase
{
public override myDerivedMustCallFunction()
{ /* code to be run in derived class here */ }
}
What do you think of this?
class myBase
{
public void myFunctionWrapper()
{
// do stuff that must happen first
// then call overridden function
this.myFunction();
}
public virtual void myFunction(){
// default implementation that can be overriden
}
}
class myInherited : myBase
{
public override void myFunction()
{
}
}
Good day,
I have a base class with a virtual method that needs to be overridden per implementation, but I would like to call the base method first before overriding.
Is there a way to accomplish this without having to actually call the method.
public class Base
{
public virtual void Method()
{
//doing some stuff here
}
}
public class Parent : Base
{
public override void Method()
{
base.Method() //need to be called ALWAYS
//then I do my thing
}
}
I cannot always rely that the base.Method() will be called in the override, so I would like to enforce it somehow. This might be a design pattern of some kind, any approach to accomplish the result will do.
One way is to define a public method in the base class, which calls another method that can be (or must be) overridden:
public class Base
{
public void Method()
{
// Do some preparatory stuff here, then call a method that might be overridden
MethodImpl()
}
protected virtual void MethodImpl() // Not accessible apart from child classes
{
}
}
public class Parent : Base
{
protected override void MethodImpl()
{
// ToDo - implement to taste
}
}
You can use the decorator design pattern, applying this pattern you can attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality:
public abstract class Component
{
public abstract void Operation();
}
public class ConcreteComponent1 : Component
{
public override void Operation()
{
//logic
}
}
public abstract class ComponentDecorator : Component
{
protected readonly Component Component;
protected ComponentDecorator(Component component)
{
Component = component;
}
public override void Operation()
{
if(Component != null)
Component.Operation();
}
}
public class ConcreteDecorator : ComponentDecorator
{
public ConcreteDecorator(Component component) : base(component)
{
}
public override void Operation()
{
base.Operation();
Console.WriteLine("Extend functionality");
}
}
Hope this helps!
If i am creating method with "override" property, derived method will not call base method implementation automatically and i will need to call it manually using "base" keyword like this:
public class A
{
public virtual void Say()
{
Console.Write("A");
}
}
public class B : A
{
public override void Say()
{
base.Say();
Console.Write("B");
}
}
So only in this case string "A" and "B" will be written to console. So the question is how can i get rid of "base.Say();" line? So i want to force every derived method "Say" to call base method from base class. Is it possible? I am looking for any solutions, even if i will be forced to use other keywords
Although it is not possible to achieve this directly, you could get the same effect by writing your own method that is not virtual, which calls the virtual after performing some fixed operation:
public class A
{
public void Say()
{
Console.Write("A");
SayImpl();
}
protected virtual void SayImpl()
{
// Do not write anything here:
// for the base class the writing is done in Say()
}
}
public class B : A
{
protected override void SayImpl()
{
Console.Write("B");
}
}
Now any class inheriting from A and implementing SayImpl() would have A prepended to its printout.
My situation is this:
public class InheritedClass : BaseClass
{
public override void SomeMethod()
{
AnotherMethod();
}
public override void AnotherMethod()
{
}
}
public class BaseClass
{
public virtual void SomeMethod()
{ }
public virtual void AnotherMethod()
{ }
}
So which method is called when I call InheritedClassInstance.SomeMethod? Does it call InheritedClassInstance.AnotherMethod, or the BaseClass's AnotherMethod?
It calls InheritedClassInstance.AnotherMethod()
If you wanted it to call the base class AnotherMethod() you would write base.AnotherMethod()
It will call the derived method on the inherited class unless you explicitly call the base method (base.AnotherMethod())
I have this situation that when AbstractMethod method is invoked from ImplementClass I want to enforce that MustBeCalled method in the AbstractClass is invoked. I’ve never come across this situation before. Thank you!
public abstract class AbstractClass
{
public abstract void AbstractMethod();
public void MustBeCalled()
{
//this must be called when AbstractMethod is invoked
}
}
public class ImplementClass : AbstractClass
{
public override void AbstractMethod()
{
//when called, base.MustBeCalled() must be called.
//how can i enforce this?
}
}
An option would be to have the Abstract class do the calling in this manner. Otherwise, there is no way in c# to require an inherited class to implement a method in a certain way.
public abstract class AbstractClass
{
public void PerformThisFunction()
{
MustBeCalled();
AbstractMethod();
}
public void MustBeCalled()
{
//this must be called when AbstractMethod is invoked
}
//could also be public if desired
protected abstract void AbstractMethod();
}
public class ImplementClass : AbstractClass
{
protected override void AbstractMethod()
{
//when called, base.MustBeCalled() must be called.
//how can i enforce this?
}
}
Doing this creates the desired public facing method in the abstract class, giving the abstract class over how and in what order things are called, while still allowing the concrete class to provide needed functionality.
How about
public abstract class AbstractClass
{
public void AbstractMethod()
{
MustBeCalled();
InternalAbstractMethod();
}
protected abstract void InternalAbstractMethod();
public void MustBeCalled()
{
//this must be called when AbstractMethod is invoked
}
}
public class ImplementClass : AbstractClass
{
protected override void InternalAbstractMethod()
{
//when called, base.MustBeCalled() must be called.
//how can i enforce this?
}
}
Why can't you just call the method in the AbstractMethod() of Implement class?
One thing the preceding solutions ignore is that ImplementClass can redefine MethodToBeCalled and not call MustBeCalled -
public abstract class AbstractClass
{
public abstract void AbstractMethod();
private void MustBeCalled()
{
//will be invoked by MethodToBeCalled();
Console.WriteLine("AbstractClass.MustBeCalled");
}
public void MethodToBeCalled()
{
MustBeCalled();
AbstractMethod();
}
}
public class ImplementClass : AbstractClass
{
public override void AbstractMethod()
{
Console.WriteLine("ImplementClass.InternalAbstractMethod");
}
public new void MethodToBeCalled() {
AbstractMethod();
}
}
If only C# allowed non-overridden methods to be sealed - like Java's final keyword!
The only way I can think of to overcome this is to use delegation rather than inheritance, because classes can be defined as sealed. And I'm using a namespace and the "internal" access modifier to prevent providing a new implementation on implementing classes. Also, the method to override must be defined as protected, otherwise users could call it directly.
namespace Something
{
public sealed class OuterClass
{
private AbstractInnerClass inner;
public OuterClass(AbstractInnerClass inner)
{
this.inner = inner;
}
public void MethodToBeCalled()
{
MustBeCalled();
inner.CalledByOuter();
}
public void MustBeCalled()
{
//this must be called when AbstractMethod is invoked
System.Console.WriteLine("OuterClass.MustBeCalled");
}
}
public abstract class AbstractInnerClass
{
internal void CalledByOuter()
{
AbstractMethod();
}
protected abstract void AbstractMethod();
}
}
public class ImplementInnerClass : Something.AbstractInnerClass
{
protected override void AbstractMethod()
{
//when called, base.MustBeCalled() must be called.
//how can i enforce this?
System.Console.WriteLine("ImplementInnerClass.AbstractMethod");
}
public new void CalledByOuter()
{
System.Console.WriteLine("doesn't work");
}
}