Ch10 this keyword page 256

arun_babu_a · October 26th, 2011, 04:14 AM

Can someone explain this keyword in page 256 step by step.I am lot confused

ChristianNagel · October 26th, 2011, 07:13 AM

Can you give more details on what you want to know? Currently I'm on the road and don't know what's exactly on page 256. You want to know what a constructor initializer is used for?
A constructor is clear?

arun_babu_a · October 27th, 2011, 12:38 AM

public void do something()
{
MyTargetClass myObj=new MyTargetClass();

myObj.DoSomethingWith(this)

}

also,,,,

In another example in samepage
in property named Somedata

return this.someData;

Please explain the use of these.

ChristianNagel · October 27th, 2011, 01:10 AM

The keyword "this" is always used to reference the current instance.

Code:

public class Foo
{
   public void DoSomething()
   {
      MyTargetClass myObj = new MyTargetClass();
      myObj.DoSomethingWith(this);
   }
   public void Bar()
   {
   }
}

public class MyTargetClass
{
   public void DoSomethingWith(Foo foo)
   {
      foo.Bar();
   }
}

The DoSomething method is an instance method of the Foo class. this is used within members of the class to reference the current instance of the class.
The DoSomethingWith method of the MyTargetClass class is declared to receive an object of type Foo as its parameter. Thus within the DoSomething method the current instance that is of type Foo can be passed to the DoSomethingWith method, and within the DoSomehingWith method every public member of Foo can be accessed.

That's very similar with properties:

Code:

private string someData;
public string SomeData
{
   get
   {
      return this.someData;
   }
   set
   {
      this.someData = value;
   }
}

SomeData is an instance property of a class. With the this keyword you access the current instance. With this.someData you access the field someData that is defined as an instance field.

In this scenario you could also write it this way:

Code:

private string someData;
public string SomeData
{
   get
   {
      return someData;
   }
   set
   {
      someData = value;
   }
}

Using the this keyword just gives a better readability to show an instance member is used instead of a local variable. The this keyword must be used in cases if there is a local variable with the same name to define the instance member is used instead of the local variable.

Hope this helps.

arun_babu_a · October 27th, 2011, 01:35 AM

[code]
public class Foo
{
public void DoSomething()
{
MyTargetClass myObj = new MyTargetClass();
myObj.DoSomethingWith(this);
}
public void Bar()
{
}
}

public class MyTargetClass
{
public void DoSomethingWith(Foo foo)
{
foo.Bar();
}
}

Please explain the parts marked bold
also Foo and MyTargetClass are seperate classes.Is it possible to call methods and properties from other classes.

ChristianNagel · October 27th, 2011, 01:43 AM

Quote:

Originally Posted by arun_babu_a

Code:

public class MyTargetClass
{
   public void DoSomethingWith(Foo foo)
   {
      foo.Bar();
   }
}

Please explain the parts marked bold
also Foo and MyTargetClass are seperate classes.Is it possible to call methods and properties from other classes.

DoSomethingWith is a method of the class MyTargetClass that does not return any value and thus is declared void, and requires a parameter of type Foo. The access modifier is public and thus it can be invoked from any type.

And:
you are always calling methods of other classes.

Here you invoke the static method WriteLine of the Console class.

Code:

Console.WriteLine("boo");

Here you invoke the ToString method of the Object class:

Code:

string s = obj.ToString();

arun_babu_a · October 27th, 2011, 01:49 AM

Then whats the need for inheritance,simply make all classes public.Right?

Or
Making public is applicable in the current context only

ChristianNagel · October 27th, 2011, 01:58 AM

There's a separate chapter that covers access modifiers in this book.
private: the member can only be accessed within the class itself
protected: the member can be accessed from the class and derived types
public: the member can be accessed from any types

Also, there are internal and protected internal access modifiers.

ChristianNagel · October 27th, 2011, 04:05 AM

Quote:

Originally Posted by arun_babu_a

Then whats the need for inheritance,simply make all classes public.Right?

I've just seen that you ask what's the need for inheritance......
No, you can't get rid of inheritance by making all classes public!
If the class is declared public it can be accessed from everywhere, and it can be used as a base class. If a class is declared as internal it can only be used as a base class within the same assembly.
Deriving from a base class gives you a is-a relation, e.g. with a base class Animal and a derived class Dog. A Dog is a Animal, and deriving it from Animal it gets every member of the base class.

You should really read chapter 8 for information on inheritance.