Socket Class

The Socket class represents a socket connection between two programs. Socket connections allow two computers to connect and exchange information. Although the programs can be running on the same computer, they don’t have to be. In fact, any two computers that are connected to the Internet can communicate via a socket.

Constructors

Constructor	Description
Socket()	Creates an unconnected socket.
Socket(InetAddress address, int port)	Creates a socket and connects it to the specified address and port.
Socket(String host, int port)	Creates a socket and connects it to the specified host and port.

Methods

Method	Description
void Close()	Closes the socket.
void connect(Inet SocketAddress endpoint)	Connects the socket to the specified address.
InetAddress getInetAddress()	Gets the address to which the socket is connected.
InputStream getInputStream()	Gets an input stream that can be used to receive data sent through this socket.
OutputStream getOutputstream()	Gets an output stream that can be used to send data through this socket.
int getPort()	Gets the port to which this socket is connected.
boolean isBound()	Indicates whether the socket is bound to a port.
boolean isClosed()	Indicates whether the socket is closed.

Creating a socket

Although the Socket class has constructors that let you connect to a specific address, the normal way to create a socket is to use the accept method of the ServerSocket class like this:

int port = 1234;

ServerSocket ss = new ServerSocket(port);

Socket s = ss.accept();

The preceding example suspends the thread until a client connects on port 1234. Then, a Socket object is created via which the programs can communicate.

Sending data via a socket

The getOutputStream method returns an object of the OutputStream class. Note that the PrintStream class constructor can accept an OutputStream object. Thus, you can use PrintStream to send data to a client program.

For example, the following code sends the text HELO to a client connected via a socket:

int port = 1234;

ServerSocket ss = new ServerSocket(port);

Socket s = ss.accept();

PrintStream out;

out = new PrintStream(s.getOutputStream(),

true);

out.println(“HELO”);

Receiving data via a socket

The getInputStream method returns an InputStream object, which can be used to receive data sent from a client program. You can then use classes such as StreamReader or Scanner to receive data from the socket.

For example, here’s a bit of code that connects to a client computer and waits until it receives the text HELO before continuing:

int port = 1234;

ServerSocket ss = new ServerSocket(port);

Socket s = ss.accept();

Scanner in = new Scanner(s.getInputStream());

String input = “”;

while (input != “HELO”)

input = in.nextLine();

// code to execute after “HELO” is received