ServicePoint Classe

Definição

Namespace:

System.Net

Assembly:

System.Net.ServicePoint.dll

Assembly:

System.dll

Assembly:

netstandard.dll

Fornece o gerenciamento de conexão para conexões HTTP.

public ref class ServicePoint

public class ServicePoint

type ServicePoint = class

Public Class ServicePoint

Herança

Object

ServicePoint

Exemplos

O exemplo de código a seguir cria um ServicePoint objeto que se conecta ao URI www.contoso.com.

// This example shows how to use the ServicePoint and ServicePointManager classes.
// The ServicePointManager class uses the ServicePoint class to manage connections
// to a remote host. The networking classes reuse service points for all 
// requests to a given URI. In fact, the same ServicePoint object 
// is used to issue requests to Internet resources identified by the same
// scheme identifier (for example,  HTTP) and host fragment (for example,  www.contoso.com).  
// This should improve your application performance. 
// Reusing service points in this way can help improve application performance.
#using <System.dll>

using namespace System;
using namespace System::Net;
using namespace System::Threading;
using namespace System::Text::RegularExpressions;
void ShowProperties( ServicePoint^ sp )
{
   Console::WriteLine( "Done calling FindServicePoint()..." );
   
   // Display the ServicePoint Internet resource address.
   Console::WriteLine( "Address = {0}", sp->Address );
   
   // Display the date and time that the ServicePoint was last 
   // connected to a host.
   Console::WriteLine( "IdleSince = {0}", sp->IdleSince );
   
   // Display the maximum length of time that the ServicePoint instance  
   // is allowed to maintain an idle connection to an Internet  
   // resource before it is recycled for use in another connection.
   Console::WriteLine( "MaxIdleTime = {0}", sp->MaxIdleTime );
   
   Console::WriteLine( "ConnectionName = {0}", sp->ConnectionName );
   
   // Display the maximum number of connections allowed on this 
   // ServicePoint instance.
   Console::WriteLine( "ConnectionLimit = {0}", sp->ConnectionLimit );
   
   // Display the number of connections associated with this 
   // ServicePoint instance.
   Console::WriteLine( "CurrentConnections = {0}", sp->CurrentConnections );
   
   if ( sp->Certificate == nullptr )
      Console::WriteLine( "Certificate = (null)" );
   else
      Console::WriteLine( "Certificate = {0}", sp->Certificate );

   if ( sp->ClientCertificate == nullptr )
      Console::WriteLine( "Client Certificate = (null)" );
   else
      Console::WriteLine( "Client Certificate = {0}", sp->ClientCertificate );

   Console::WriteLine( "ProtocolVersion = {0}", sp->ProtocolVersion->ToString() );
   Console::WriteLine( "SupportsPipelining = {0}", sp->SupportsPipelining );
   
   Console::WriteLine( "UseNagleAlgorithm = {0} ", sp->UseNagleAlgorithm.ToString() );
   Console::WriteLine( "Expect 100-continue = {0}", sp->Expect100Continue.ToString() );
   
}


void makeWebRequest( int hashCode, String^ Uri )
{
   HttpWebResponse^ res = nullptr;
   
   // Make sure that the idle time has elapsed, so that a new 
   // ServicePoint instance is created.
   Console::WriteLine( "Sleeping for 2 sec." );
   Thread::Sleep( 2000 );
   try
   {
      
      // Create a request to the passed URI.
      HttpWebRequest^ req = dynamic_cast<HttpWebRequest^>(WebRequest::Create( Uri ));
      Console::WriteLine( "\nConnecting to {0} ............", Uri );
      
      // Get the response object.
      res = dynamic_cast<HttpWebResponse^>(req->GetResponse());
      Console::WriteLine( "Connected.\n" );
      ServicePoint^ currentServicePoint = req->ServicePoint;
      
      // Display new service point properties.
      int currentHashCode = currentServicePoint->GetHashCode();
      Console::WriteLine( "New service point hashcode: {0}", currentHashCode );
      Console::WriteLine( "New service point max idle time: {0}", currentServicePoint->MaxIdleTime );
      Console::WriteLine( "New service point is idle since {0}", currentServicePoint->IdleSince );
      
      // Check that a new ServicePoint instance has been created.
      if ( hashCode == currentHashCode )
            Console::WriteLine( "Service point reused." );
      else
            Console::WriteLine( "A new service point created." );
   }
   catch ( Exception^ e ) 
   {
      Console::WriteLine( "Source : {0}", e->Source );
      Console::WriteLine( "Message : {0}", e->Message );
   }
   finally
   {
      if ( res != nullptr )
            res->Close();
   }

}


// Show the user how to use this program when wrong inputs are entered.
void showUsage()
{
   Console::WriteLine( "Enter the proxy name as follows:" );
   Console::WriteLine( "\tcs_servicepoint proxyName" );
}


int main()
{
   array<String^>^args = Environment::GetCommandLineArgs();
   int port = 80;
   
   // Define a regular expression to parse the user's input.
   // This is a security check. It allows only
   // alphanumeric input strings between 2 to 40 characters long.
   Regex^ rex = gcnew Regex( "^[a-zA-Z]\\w{1,39}$" );
   if ( args->Length < 2 )
   {
      showUsage();
      return  -1;
   }

   String^ proxy = args[ 1 ];
   if ( (rex->Match(proxy))->Success != true )
   {
      Console::WriteLine( "Input string format not allowed." );
      return  -1;
   }

   String^ proxyAdd = String::Format( "http://{0}:{1}", proxy, port );
   
   // Create a proxy object.  
   WebProxy^ DefaultProxy = gcnew WebProxy( proxyAdd,true );
   
   // Set the proxy that all HttpWebRequest instances use.
   WebRequest::DefaultWebProxy = DefaultProxy;
   
   // Get the base interface for proxy access for the 
   // WebRequest-based classes.
   IWebProxy^ Iproxy = WebRequest::DefaultWebProxy;

   
   // Set the maximum number of ServicePoint instances to 
   // maintain. If a ServicePoint instance for that host already 
   // exists when your application requests a connection to
   // an Internet resource, the ServicePointManager object
   // returns this existing ServicePoint instance. If none exists 
   // for that host, it creates a new ServicePoint instance.
   ServicePointManager::MaxServicePoints = 4;
   
   // Set the maximum idle time of a ServicePoint instance to 10 seconds.
   // After the idle time expires, the ServicePoint object is eligible for
   // garbage collection and cannot be used by the ServicePointManager.
   ServicePointManager::MaxServicePointIdleTime = 10000;
   
   ServicePointManager::UseNagleAlgorithm = true;
   ServicePointManager::Expect100Continue = true;
   ServicePointManager::CheckCertificateRevocationList = true;
   ServicePointManager::DefaultConnectionLimit = ServicePointManager::DefaultPersistentConnectionLimit;
   
   // Create the Uri object for the resource you want to access.
   Uri^ MS = gcnew Uri( "http://msdn.microsoft.com/" );
   
   // Use the FindServicePoint method to find an existing 
   // ServicePoint object or to create a new one.   
   ServicePoint^ servicePoint = ServicePointManager::FindServicePoint( MS, Iproxy );
   ShowProperties( servicePoint );
   int hashCode = servicePoint->GetHashCode();
   Console::WriteLine( "Service point hashcode: {0}", hashCode );
   
   // Make a request with the same scheme identifier and host fragment
   // used to create the previous ServicePoint object.
   makeWebRequest( hashCode, "http://msdn.microsoft.com/library/" );
}

// This example shows how to use the ServicePoint and ServicePointManager classes.
// The ServicePointManager class uses the ServicePoint class to manage connections
// to a remote host. The networking classes reuse service points for all
// requests to a given URI. In fact, the same ServicePoint object
// is used to issue requests to Internet resources identified by the same
// scheme identifier (for example,  HTTP) and host fragment (for example,  www.contoso.com).
// This should improve your application performance.
// Reusing service points in this way can help improve application performance.
using System;
using System.Net;
using System.Threading;
using System.Text.RegularExpressions;

namespace Mssc.Services.ConnectionManagement
{
    class TestServicePoint
    {
        private static void ShowProperties(ServicePoint sp)
        {
            Console.WriteLine("Done calling FindServicePoint()...");

            // Display the ServicePoint Internet resource address.
            Console.WriteLine("Address = {0} ", sp.Address.ToString());

            // Display the date and time that the ServicePoint was last
            // connected to a host.
            Console.WriteLine("IdleSince = " + sp.IdleSince.ToString());

            // Display the maximum length of time that the ServicePoint instance
            // is allowed to maintain an idle connection to an Internet
            // resource before it is recycled for use in another connection.
            Console.WriteLine("MaxIdleTime = " + sp.MaxIdleTime);

            Console.WriteLine("ConnectionName = " + sp.ConnectionName);

            // Display the maximum number of connections allowed on this
            // ServicePoint instance.
            Console.WriteLine("ConnectionLimit = " + sp.ConnectionLimit);

            // Display the number of connections associated with this
            // ServicePoint instance.
            Console.WriteLine("CurrentConnections = " + sp.CurrentConnections);

            if (sp.Certificate == null)
                Console.WriteLine("Certificate = (null)");
            else
                Console.WriteLine("Certificate = " + sp.Certificate.ToString());

            if (sp.ClientCertificate == null)
                Console.WriteLine("ClientCertificate = (null)");
            else
                Console. WriteLine("ClientCertificate = " + sp.ClientCertificate.ToString());

            Console.WriteLine("ProtocolVersion = " + sp.ProtocolVersion.ToString());
            Console.WriteLine("SupportsPipelining = " + sp.SupportsPipelining);

            Console.WriteLine("UseNagleAlgorithm = " + sp.UseNagleAlgorithm.ToString());
            Console.WriteLine("Expect 100-continue = " + sp.Expect100Continue.ToString());
        }

        private static void makeWebRequest(int hashCode, string Uri)
        {
            HttpWebResponse res = null;

            // Make sure that the idle time has elapsed, so that a new
            // ServicePoint instance is created.
            Console.WriteLine("Sleeping for 2 sec.");
            Thread.Sleep(2000);
            try
            {
                // Create a request to the passed URI.
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(Uri);

                Console.WriteLine("\nConnecting to " + Uri + " ............");

                // Get the response object.
                res = (HttpWebResponse)req.GetResponse();
                Console.WriteLine("Connected.\n");

                ServicePoint currentServicePoint = req.ServicePoint;

                // Display new service point properties.
                int currentHashCode = currentServicePoint.GetHashCode();

                Console.WriteLine("New service point hashcode: " + currentHashCode);
                Console.WriteLine("New service point max idle time: " + currentServicePoint.MaxIdleTime);
                Console.WriteLine("New service point is idle since " + currentServicePoint.IdleSince );

                // Check that a new ServicePoint instance has been created.
                if (hashCode == currentHashCode)
                    Console.WriteLine("Service point reused.");
                else
                    Console.WriteLine("A new service point created.") ;
            }
            catch (Exception e)
            {
                Console.WriteLine("Source : " + e.Source);
                Console.WriteLine("Message : " + e.Message);
            }
            finally
            {
                if (res != null)
                    res.Close();
            }
        }

        // Show the user how to use this program when wrong inputs are entered.
        private static void showUsage()
        {
            Console.WriteLine("Enter the proxy name as follows:");
            Console.WriteLine("\tcs_servicepoint proxyName");
        }

        public static void Main(string[] args)
        {
            int port = 80;

            // Define a regular expression to parse the user's input.
            // This is a security check. It allows only
            // alphanumeric input strings between 2 to 40 characters long.
            Regex rex = new Regex(@"^[a-zA-Z]\w{1,39}$");

            if (args.Length < 1)
            {
                showUsage();
                return;
            }
            string proxy = args[0];

            if ((rex.Match(proxy)).Success != true)
            {
                Console.WriteLine("Input string format not allowed.");
                return;
            }
            string proxyAdd = "http://" + proxy + ":" + port;

            // Create a proxy object.
            WebProxy DefaultProxy = new WebProxy(proxyAdd, true);

            // Set the proxy that all HttpWebRequest instances use.
            WebRequest.DefaultWebProxy = DefaultProxy;

            // Get the base interface for proxy access for the
            // WebRequest-based classes.
            IWebProxy Iproxy = WebRequest.DefaultWebProxy;

            // Set the maximum number of ServicePoint instances to
            // maintain. If a ServicePoint instance for that host already
            // exists when your application requests a connection to
            // an Internet resource, the ServicePointManager object
            // returns this existing ServicePoint instance. If none exists
            // for that host, it creates a new ServicePoint instance.
            ServicePointManager.MaxServicePoints = 4;

            // Set the maximum idle time of a ServicePoint instance to 10 seconds.
            // After the idle time expires, the ServicePoint object is eligible for
            // garbage collection and cannot be used by the ServicePointManager object.
            ServicePointManager.MaxServicePointIdleTime = 10000;

            ServicePointManager.UseNagleAlgorithm = true;
            ServicePointManager.Expect100Continue = true;
            ServicePointManager.CheckCertificateRevocationList = true;
            ServicePointManager.DefaultConnectionLimit = ServicePointManager.DefaultPersistentConnectionLimit;
            // Create the Uri object for the resource you want to access.
            Uri MS = new Uri("http://msdn.microsoft.com/");

            // Use the FindServicePoint method to find an existing
            // ServicePoint object or to create a new one.
            ServicePoint servicePoint = ServicePointManager.FindServicePoint(MS, Iproxy);

            ShowProperties(servicePoint);

            int hashCode = servicePoint.GetHashCode();

            Console.WriteLine("Service point hashcode: " + hashCode);

            // Make a request with the same scheme identifier and host fragment
            // used to create the previous ServicePoint object.
            makeWebRequest(hashCode, "http://msdn.microsoft.com/library/");
        }
    }
}

' This example shows how to use the ServicePoint and ServicePointManager classes.
' The ServicePointManager class uses the ServicePoint class to manage connections
' to a remote host. The networking classes reuse service points for all 
' requests to a given URI. In fact, the same ServicePoint object 
' is used to issue requests to Internet resources identified by the same
' scheme identifier (for example,  HTTP) and host fragment (for example,  www.contoso.com).  
' Reusing service points in this way can help improve application  performance.

Imports System.Net
Imports System.Threading
Imports System.Text.RegularExpressions

Namespace Mssc.Services.ConnectionManagement
    Module M_TestServicePoint

        Class TestServicePoint
            Private Shared Sub ShowProperties(ByVal sp As ServicePoint)

                Console.WriteLine("Done calling FindServicePoint")

                ' Display the ServicePoint Internet resource address.
                Console.WriteLine(("Address = " + sp.Address.ToString()))

                ' Display the date and time that the ServicePoint was last 
                ' connected to a host.
                Console.WriteLine(("IdleSince = " + sp.IdleSince.ToString()))


                ' Display the maximum length of time that the ServicePoint instance 
                ' is allowed to maintain an idle connection to an Internet  
                ' resource before it is recycled for use in another connection.
                Console.WriteLine(("MaxIdleTime = " + sp.MaxIdleTime.ToString()))

                Console.WriteLine(("ConnectionName = " + sp.ConnectionName))

                ' Display the maximum number of connections allowed on this 
                ' ServicePoint instance.
                Console.WriteLine(("ConnectionLimit = " + sp.ConnectionLimit.ToString()))

                ' Display the number of connections associated with this 
                ' ServicePoint instance.
                Console.WriteLine(("CurrentConnections = " + sp.CurrentConnections.ToString()))

                If sp.Certificate Is Nothing Then
                    Console.WriteLine("Certificate = (null)")
                Else
                    Console.WriteLine(("Certificate = " + sp.Certificate.ToString()))
                End If

                If sp.ClientCertificate Is Nothing Then
                    Console.WriteLine("ClientCertificate = (null)")
                Else
                    Console.WriteLine(("ClientCertificate = " + sp.ClientCertificate.ToString()))
                End If

                Console.WriteLine("ProtocolVersion = " + sp.ProtocolVersion.ToString())
                Console.WriteLine(("SupportsPipelining = " + sp.SupportsPipelining.ToString()))


                Console.WriteLine("UseNagleAlgorithm = " + sp.UseNagleAlgorithm.ToString())
                Console.WriteLine("Expect 100-continue = " + sp.Expect100Continue.ToString())
            End Sub





            Private Shared Sub makeWebRequest(ByVal hashCode As Integer, ByVal Uri As String)
                Dim res As HttpWebResponse = Nothing

                ' Make sure that the idle time has elapsed, so that a new 
                ' ServicePoint instance is created.
                Console.WriteLine("Sleeping for 2 sec.")
                Thread.Sleep(2000)

                Try
                    ' Create a request to the passed URI.
                    Dim req As HttpWebRequest = CType(WebRequest.Create(Uri), HttpWebRequest)
                    Console.WriteLine((ControlChars.Lf + "Connecting to " + Uri + " ............"))

                    ' Get the response object.
                    res = CType(req.GetResponse(), HttpWebResponse)
                    Console.WriteLine("Connected." + ControlChars.Lf)
                    Dim currentServicePoint As ServicePoint = req.ServicePoint

                    ' Display new service point properties.
                    Dim currentHashCode As Integer = currentServicePoint.GetHashCode()
                    Console.WriteLine(("New service point hashcode: " + currentHashCode.ToString()))
                    Console.WriteLine(("New service point max idle time: " + currentServicePoint.MaxIdleTime.ToString()))
                    Console.WriteLine(("New service point is idle since " + currentServicePoint.IdleSince.ToString()))

                    ' Check that a new ServicePoint instance has been created.
                    If hashCode = currentHashCode Then
                        Console.WriteLine("Service point reused.")
                    Else
                        Console.WriteLine("A new service point created.")
                    End If
                Catch e As Exception
                    Console.WriteLine(("Source : " + e.Source))
                    Console.WriteLine(("Message : " + e.Message))
                Finally
                    If Not (res Is Nothing) Then
                        res.Close()
                    End If
                End Try
            End Sub


            ' Show the user how to use this program when wrong inputs are entered.
            Private Shared Sub showUsage()
                Console.WriteLine("Enter the proxy name as follows:")
                Console.WriteLine(ControlChars.Tab + "vb_servicepoint proxyName")
            End Sub

            ' This is the program entry point. It allows the user to enter 
            ' a server name that is used to locate its current homepage.
            Public Shared Sub Main(ByVal args() As String)
                Dim proxy As String = Nothing
                Dim port As Integer = 80

                ' Define a regular expression to parse the user's input.
                ' This is a security check. It allows only
                ' alphanumeric input strings between 2 to 40 characters long.
                Dim rex As New Regex("^[a-zA-Z]\w{1,39}$")

                If args.Length = 0 Then
                    ' Show how to use this program.
                    showUsage()
                    Return
                End If

                proxy = args(0)
                If (Not (rex.Match(proxy)).Success) Then
                    Console.WriteLine("Input string format not allowed.")
                    Return
                End If

                ' Create a proxy object.  
                Dim proxyAdd As String
                proxyAdd = "http://" + proxy + ":" + port.ToString()


                Dim DefaultProxy As New WebProxy(proxyAdd, True)

                ' Set the proxy that all HttpWebRequest instances use.
                WebRequest.DefaultWebProxy = DefaultProxy


                ' Get the base interface for proxy access for the 
                ' WebRequest-based classes.
                Dim Iproxy As IWebProxy = WebRequest.DefaultWebProxy

                ' Set the maximum number of ServicePoint instances to maintain.
                ' Note that, if a ServicePoint instance for that host already 
                ' exists when your application requests a connection to
                ' an Internet resource, the ServicePointManager object
                ' returns this existing ServicePoint. If none exists 
                ' for that host, it creates a new ServicePoint instance.
                ServicePointManager.MaxServicePoints = 4

                ' Set the maximum idle time of a ServicePoint instance to 10 seconds.
                ' After the idle time expires, the ServicePoint object is eligible for
                ' garbage collection and cannot be used by the ServicePointManager.
                ServicePointManager.MaxServicePointIdleTime = 10000


                ServicePointManager.UseNagleAlgorithm = True
                ServicePointManager.Expect100Continue = True
                ServicePointManager.CheckCertificateRevocationList = True
                ServicePointManager.DefaultConnectionLimit = _
                    ServicePointManager.DefaultPersistentConnectionLimit
                ' Create the Uri object for the resource you want to access.
                Dim MS As New Uri("http://msdn.microsoft.com/")

                ' Use the FindServicePoint method to find an existing 
                ' ServicePoint object or to create a new one.   
                Dim servicePoint As ServicePoint = ServicePointManager.FindServicePoint(MS, Iproxy)
                ShowProperties(servicePoint)
                Dim hashCode As Integer = servicePoint.GetHashCode()
                Console.WriteLine(("Service point hashcode: " + hashCode.ToString()))

                ' Make a request with the same scheme identifier and host fragment
                ' used to create the previous ServicePoint object.
                makeWebRequest(hashCode, "http://msdn.microsoft.com/library/")

            End Sub


        End Class

    End Module
End Namespace

Comentários

A ServicePoint classe lida com conexões com um recurso da Internet com base nas informações de host passadas no URI (Uniform Resource Identifier) do recurso. A conexão inicial com o recurso determina as informações que o ServicePoint objeto mantém, que são compartilhadas por todas as solicitações subsequentes a esse recurso.

ServicePoint os objetos são gerenciados pela ServicePointManager classe e são criados, se necessário, pelo ServicePointManager.FindServicePoint método. ServicePoint os objetos nunca são criados diretamente, mas sempre são criados e gerenciados pela ServicePointManager classe. O número máximo de ServicePoint objetos que podem ser criados é definido pela ServicePointManager.MaxServicePoints propriedade.

Cada ServicePoint objeto mantém sua conexão com um recurso da Internet até ficar ocioso por mais tempo do que o tempo especificado na MaxIdleTime propriedade. Quando um ServicePoint excede o MaxIdleTime valor, ele pode ser reciclado para outra conexão. O valor padrão é MaxIdleTime definido pela ServicePointManager.MaxServicePointIdleTime propriedade.

Quando a ConnectionLeaseTimeout propriedade é definida como um valor diferente de -1 e após o tempo especificado decorrido, uma conexão ativa ServicePoint é fechada depois que ela atende à próxima solicitação. Isso é útil para aplicativos que não exigem conexões ativas que são abertas indefinidamente, pois são por padrão.

Observação

Em condições de alta carga, alguns aplicativos podem ficar sem threads gratuitos no ThreadPool, o que pode levar a um desempenho ruim do sistema (como tempos de transação altos e variáveis).

Importante

Não recomendamos que você use a ServicePoint classe para um novo desenvolvimento. Em vez disso, use a System.Net.Http.HttpClient classe.

Propriedades

Address	Obtém o URI (Uniform Resource Identifier) do servidor ao qual este objeto ServicePoint se conecta.
BindIPEndPointDelegate	Especifica o delegado para associar um IPEndPoint local com uma ServicePoint.
Certificate	Obtém o certificado recebido para este objeto ServicePoint.
ClientCertificate	Obtém o último certificado do cliente enviado ao servidor.
ConnectionLeaseTimeout	Obtém ou define o número de milissegundos após os quais uma conexão de ServicePoint ativa é fechada.
ConnectionLimit	Obtém ou define o número máximo de conexões permitidas neste objeto ServicePoint.
ConnectionName	Obtém o nome da conexão.
CurrentConnections	Obtém o número de conexões abertas associadas a este objeto ServicePoint.
Expect100Continue	Obtém ou define um valor Boolean que determina se o comportamento 100-Continue é usado.
IdleSince	Obtém a data e a hora em que o objeto ServicePoint estava conectado pela última vez a um host.
MaxIdleTime	Obtém ou define por quanto tempo uma conexão associada ao objeto ServicePoint pode permanecer ociosa antes que a conexão seja fechada.
ProtocolVersion	Obtém a versão do protocolo HTTP que o objeto ServicePoint usa.
ReceiveBufferSize	Obtém ou define o tamanho do buffer de recebimento para o soquete usado por este ServicePoint.
SupportsPipelining	Indica se o objeto ServicePoint dá suporte a conexões por pipeline.
UseNagleAlgorithm	Obtém ou define um valor Boolean que determina se o algoritmo de Nagle é usado em conexões gerenciadas por este objeto ServicePoint.

Métodos

CloseConnectionGroup(String)	Remove o grupo de conexões especificado deste objeto ServicePoint.
Equals(Object)	Determina se o objeto especificado é igual ao objeto atual. (Herdado de Object)
GetHashCode()	Retorna um valor de hash para uma instância de ServicePoint.
GetHashCode()	Serve como a função de hash padrão. (Herdado de Object)
GetType()	Obtém o Type da instância atual. (Herdado de Object)
MemberwiseClone()	Cria uma cópia superficial do Object atual. (Herdado de Object)
SetTcpKeepAlive(Boolean, Int32, Int32)	Habilita ou desabilita a opção keep alive em uma conexão TCP.
ToString()	Retorna uma cadeia de caracteres que representa o objeto atual. (Herdado de Object)