Namespace and Assemblies
The first line of the “Hello, C# World!” program was this:
using System;
To define .NET classes in a category so they’d be easy to recognize, Microsoft used the C++ class-packaging concept know as namespaces. A namespace is simply a grouping of related classes. The root of all namespaces is the System namespace. If you see namespaces in the .NET library, each class is defined in a group of similar category. For example, The System.Data namespace only possesses data-related classes, and System.Multithreading contains only multithreading classes.
When you create a new application using visual C#, you see that each application is defined as a namespace and that all classes belong to that namespace. You can access these classes from other application by referencing their namespaces.
Listing 2 Namespace wrapper for the hello class
namespace MyOtherNamespace
{
class MyOtherClass
{
public void Hello()
{
Console.WriteLine ("Hello, C# World!");
}
}
}
Listing 3. Calling my other Namespace Name space members
using System;
using MyOtherNamespace;
// Caller namespace
namespace HelloWorldNamespace
{
class Hello
{
static void Main()
{
MyOtherClass cls = new MyOtherClass();
cls.Hello();
}
}
}
// Called namespace
namespace MyOtherNamespace
{
class MyOtherClass
{
public void Hello()
{
Console.WriteLine("Hello, C# World!");
}
}
}
As you have seen in listing 3, you include a namespace by adding the using directly. You can also reference a namespace direct without the using directive. Listing 4 shows you how to use MyOtherClass of MyOtherNamespace.
Listing 4. Calling the HelloWorld namespace member from the MyOtherNamespace
// Caller namespace
namespace HelloWorldNamespace
{
class Hello
{
static void Main()
{
MyOtherNamespace.MyOtherClass cls =
new MyOtherNamespace.MyOtherClass();
cls.Hello();
}
}
}
Standard Input and Output Streams
The System.Console class provides the capability to read streams from and write streams to the System console. It also defines functionality for error streams. The Read operation reads data from the console to the standard input stream, and the Write operation writes data to the standard output stream. The standard error stream is responsible for storing error data. These streams are the automatically associated with the system console.
The error, in, and out properties of the Console class represents standard error output, standard input and standard output streams. In the standard output stream, the Read method reads the next character, and the ReadLine method reads the next line. The Write and WriteLine methods write the data to the standard output stream. Table 1 describes some of the console class methods.
Table 1. The System.Console Class methods
METHOD
|
DESCRIPTION
|
EXAMPLE
|
|
Read |
Reads a single character |
int i = Console.Read(); |
|
ReadLline |
Reads a line |
string str = Console.ReadLine(); |
|
Write |
Writes a line |
Console.Write ("Write: 1"); |
|
WriteLine |
Writes a line followed by a line terminator |
Console.WriteLine("Test Output Data with Line"); |
|
|
|
|
Listing 5 shows you how to use the Console class and its members
Listing 5. Console class example
using System;
namespace ConsoleSamp
{
class Classs1
{
static void Main(string[] args)
{
Console.Write("Standard Input and Output Exmaple");
Console.WriteLine("");
Console.WriteLine("= = = = = = = = ");
Console.WriteLine("Enter your full name . . .");
string name = Console.ReadLine();
Console.WriteLine("Output: Your name is : " + name);
Console.ReadLine();
}
}
}
Figure 2. The console class methods output
The Object Class
>>As described, in the .NET framework, all types are represented as objects and are derived from the Object class. The Object class defines five methods: Equals, ReferenceEquals GetHashCode, GetType and ToString. Table 2 describes these methods, which are available to all types in the .NET library.
Table 2. Object class methods
|
METHOD |
DESCRIPTION |
|
GetType |
Return type of the object. |
|
Equals |
Compares two object instances. Returns true if they’re Equal; otherwise false. |
|
ReferenceEquals |
Compares two object instances. Returns true if both are Same instance; otherwise false. |
|
ToString |
Converts an instance to a string type. |
|
GetHashCode |
Return hash code for an object. |
The following sections discuss the object class methods in more detail.
The GetType method
You can use the Type class to retrieve type information from the object. The GetType method of an object return a type object, which you can use to get information on an object such as its name, namespace, base type, and so on. Listing 6 retrieves the information of objects. In Listing 6, you get the type of the Object and System.String classes.Listing 6 GetType example
using System;
class TypeClass
{
static void Main(string [] args)
{
//create object of type object and string
Object cls1 = new Object ();
System.String cls2 = "Test string";
// Call Get Type to return the type
Type type1 = cls1.GetType( );
Type type2 =cls2.GetType( );
// Object class output
Console.WriteLine(type1.BaseType);
Console.WriteLine(type1.Name);
Console.WriteLine(type1.FullName);
Console.WriteLine(type1.Namespace);
// String output
Console.WriteLine(type2.BaseType);
Console.WriteLine(type2.Name);
Console.WriteLine(type2.FullName);
Console.WriteLine(type2.Namespace);
}
}
Figure 3 shows the output of listing 6.
Figure 3. Output of listing
The Equals and ReferenceEqual Methods
The Equals method in the Object class can compare two objects. The ReferenceEqual method can compare the two objects’ instances. For example:
Console.WriteLine(Object.Equals(cls1, cls2));
Console.WriteLine(Object.Equals(str1, str2));
See listing 7 get type, equal, and reference Equals
Listing 7. Get Type, Equal, and ReferenceEquals
using System;
namespace TypesSamp
{
//define class 1
public class Class1: object
{
private void Method1()
{
Console.WriteLine("1 method");
}
}
// Define class 2
public class Class2: Class1
{
private void Method2( )
{
Console.WriteLine("2 method");
}
}
class TypeClass
{
static void Main(string [] args)
{
Class1 cls1 = new Class1();
Class2 cls2 = new Class2();
Console.WriteLine ("= = = = = = = = = = ");
Console.WriteLine ("Type Information");
Console.WriteLine ("= = = = = = = = = =");
// Getting type information
Type type1 =cls1.GetType( );
Type type2 = cls2.GetType( );
Console.WriteLine(type1.BaseType);
Console.WriteLine(type1.Name);
Console.WriteLine(type1.FullName);
Console.WriteLine(type1.Namespace);
// Comparing two objects
string str1 = "Test";
string str2 = "Test";
Console.WriteLine(" = = = = = = = = = = = ");
Console.WriteLine("comparison of two objects");
Console.WriteLine(object.Equals(cls1, cls2));
Console.WriteLine(object.Equals(str1, str2));
}
}
}
Figure 4 shows the output of listing 7.
Figure 4 get type and compare objects code output
The ToString Method and String Conversion
The ToString method of the Object class converts a type to a string type.Listing 8 shows an example of the ToString method.
using System;
namespace ToStringSamp
{
class Test
{
static void Main(string [] args)
{
int num1 =8;
float num2 =162.034f;
Console.WriteLine(num1.ToString( ));
Console.WriteLine(num2.ToString( ));
}
}
}
The GetHashCode method
A hashtable (also commonly known as a map or dictionary) is a data structure that stores one or more key- value pairs of data. Hashtables are useful when you want fast access to a list of data through a key (which can be a number, letter, string, or any object). In .NET the HashTable class represents a hashtable, which is implemented based on a hashing algorithm. This class also provides methods and constructors to define the size of the hash table. You can use the Add and Remove methods to add and remove items from a hashtable. The Count property of the HashTable class returns the number of items in a hashtable.
The GetHashCode method returns the hash code of an object. To return a hash code for a type, you must override the GetHashCode method. An integer value is returned, which represents whether an object is available in a hashtable.
Two other useful methods of the object class are MemberWiseClone and Finalize methods. The MemberWiseClone method creates a shallow copy of an object, which can be used as a clone of an object. The Finalize method acts as a destructor and can clean up the resources before the garbage collector calls the object. You need to override this method and write your own code to clean up the resources. The garbage collector automatically calls the Finalize method if an object is no longer in use.