SocketImpl (Java Platform SE 8 )
Keywords: java.net.SocketImpl class
Date: 2026-03-16

compact1, compact2, compact3
java.net

## Class SocketImpl

- java.lang.Object
- - java.net.SocketImpl

- All Implemented Interfaces:
    SocketOptions

      public abstract class SocketImpl
      extends Object
      implements SocketOptions

  The abstract class `SocketImpl` is a common superclass of all classes that actually implement sockets. It is used to create both client and server sockets.

  A "plain" socket implements these methods exactly as described, without attempting to go through a firewall or proxy.

  Since:
    JDK1.0

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected InetAddress` | `address` The IP address of the remote end of this socket.
    `protected FileDescriptor` | `fd` The file descriptor object for this socket.
    `protected int` | `localport` The local port number to which this socket is connected.
    `protected int` | `port` The port number on the remote host to which this socket is connected.

    - ### Fields inherited from interface java.net.SocketOptions

      `IP_MULTICAST_IF, IP_MULTICAST_IF2, IP_MULTICAST_LOOP, IP_TOS, SO_BINDADDR, SO_BROADCAST, SO_KEEPALIVE, SO_LINGER, SO_OOBINLINE, SO_RCVBUF, SO_REUSEADDR, SO_SNDBUF, SO_TIMEOUT, TCP_NODELAY`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SocketImpl()`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected abstract void` | `accept(SocketImpl s)` Accepts a connection.
    `protected abstract int` | `available()` Returns the number of bytes that can be read from this socket without blocking.
    `protected abstract void` | `bind(InetAddress host, int port)` Binds this socket to the specified local IP address and port number.
    `protected abstract void` | `close()` Closes this socket.
    `protected abstract void` | `connect(InetAddress address, int port)` Connects this socket to the specified port number on the specified host.
    `protected abstract void` | `connect(SocketAddress address, int timeout)` Connects this socket to the specified port number on the specified host.
    `protected abstract void` | `connect(String host, int port)` Connects this socket to the specified port on the named host.
    `protected abstract void` | `create(boolean stream)` Creates either a stream or a datagram socket.
    `protected FileDescriptor` | `getFileDescriptor()` Returns the value of this socket's `fd` field.
    `protected InetAddress` | `getInetAddress()` Returns the value of this socket's `address` field.
    `protected abstract InputStream` | `getInputStream()` Returns an input stream for this socket.
    `protected int` | `getLocalPort()` Returns the value of this socket's `localport` field.
    `protected abstract OutputStream` | `getOutputStream()` Returns an output stream for this socket.
    `protected int` | `getPort()` Returns the value of this socket's `port` field.
    `protected abstract void` | `listen(int backlog)` Sets the maximum queue length for incoming connection indications (a request to connect) to the `count` argument.
    `protected abstract void` | `sendUrgentData(int data)` Send one byte of urgent data on the socket.
    `protected void` | `setPerformancePreferences(int connectionTime, int latency, int bandwidth)` Sets performance preferences for this socket.
    `protected void` | `shutdownInput()` Places the input stream for this socket at "end of stream".
    `protected void` | `shutdownOutput()` Disables the output stream for this socket.
    `protected boolean` | `supportsUrgentData()` Returns whether or not this SocketImpl supports sending urgent data.
    `String` | `toString()` Returns the address and port of this socket as a `String`.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface java.net.SocketOptions

      `getOption, setOption`

- - ### Field Detail

    - #### fd

          protected FileDescriptor fd

      The file descriptor object for this socket.

    - #### address

          protected InetAddress address

      The IP address of the remote end of this socket.

    - #### port

          protected int port

      The port number on the remote host to which this socket is connected.

    - #### localport

          protected int localport

      The local port number to which this socket is connected.

  - ### Constructor Detail

    - #### SocketImpl

          public SocketImpl()

  - ### Method Detail

    - #### create

          protected abstract void create(boolean stream)
                                  throws IOException

      Creates either a stream or a datagram socket.
      Parameters:
        `stream` - if `true`, create a stream socket; otherwise, create a datagram socket.
      Throws:
        `IOException` - if an I/O error occurs while creating the socket.

    - #### connect

          protected abstract void connect(String host,
                                          int port)
                                   throws IOException

      Connects this socket to the specified port on the named host.
      Parameters:
        `host` - the name of the remote host.
        `port` - the port number.
      Throws:
        `IOException` - if an I/O error occurs when connecting to the remote host.

    - #### connect

          protected abstract void connect(InetAddress address,
                                          int port)
                                   throws IOException

      Connects this socket to the specified port number on the specified host.
      Parameters:
        `address` - the IP address of the remote host.
        `port` - the port number.
      Throws:
        `IOException` - if an I/O error occurs when attempting a connection.

    - #### connect

          protected abstract void connect(SocketAddress address,
                                          int timeout)
                                   throws IOException

      Connects this socket to the specified port number on the specified host. A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.
      Parameters:
        `address` - the Socket address of the remote host.
        `timeout` - the timeout value, in milliseconds, or zero for no timeout.
      Throws:
        `IOException` - if an I/O error occurs when attempting a connection.
      Since:
        1.4

    - #### bind

          protected abstract void bind(InetAddress host,
                                       int port)
                                throws IOException

      Binds this socket to the specified local IP address and port number.
      Parameters:
        `host` - an IP address that belongs to a local interface.
        `port` - the port number.
      Throws:
        `IOException` - if an I/O error occurs when binding this socket.

    - #### listen

          protected abstract void listen(int backlog)
                                  throws IOException

      Sets the maximum queue length for incoming connection indications (a request to connect) to the `count` argument. If a connection indication arrives when the queue is full, the connection is refused.
      Parameters:
        `backlog` - the maximum length of the queue.
      Throws:
        `IOException` - if an I/O error occurs when creating the queue.

    - #### accept

          protected abstract void accept(SocketImpl s)
                                  throws IOException

      Accepts a connection.
      Parameters:
        `s` - the accepted connection.
      Throws:
        `IOException` - if an I/O error occurs when accepting the connection.

    - #### getInputStream

          protected abstract InputStream getInputStream()
                                                 throws IOException

      Returns an input stream for this socket.
      Returns:
        a stream for reading from this socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the input stream.

    - #### getOutputStream

          protected abstract OutputStream getOutputStream()
                                                   throws IOException

      Returns an output stream for this socket.
      Returns:
        an output stream for writing to this socket.
      Throws:
        `IOException` - if an I/O error occurs when creating the output stream.

    - #### available

          protected abstract int available()
                                    throws IOException

      Returns the number of bytes that can be read from this socket without blocking.
      Returns:
        the number of bytes that can be read from this socket without blocking.
      Throws:
        `IOException` - if an I/O error occurs when determining the number of bytes available.

    - #### close

          protected abstract void close()
                                 throws IOException

      Closes this socket.
      Throws:
        `IOException` - if an I/O error occurs when closing this socket.

    - #### shutdownInput

          protected void shutdownInput()
                                throws IOException

      Places the input stream for this socket at "end of stream". Any data sent to this socket is acknowledged and then silently discarded. If you read from a socket input stream after invoking this method on the socket, the stream's `available` method will return 0, and its `read` methods will return `-1` (end of stream).
      Throws:
        `IOException` - if an I/O error occurs when shutting down this socket.
      Since:
        1.3
      See Also:
        `Socket.shutdownOutput()`, `Socket.close()`, `Socket.setSoLinger(boolean, int)`

    - #### shutdownOutput

          protected void shutdownOutput()
                                 throws IOException

      Disables the output stream for this socket. For a TCP socket, any previously written data will be sent followed by TCP's normal connection termination sequence. If you write to a socket output stream after invoking shutdownOutput() on the socket, the stream will throw an IOException.
      Throws:
        `IOException` - if an I/O error occurs when shutting down this socket.
      Since:
        1.3
      See Also:
        `Socket.shutdownInput()`, `Socket.close()`, `Socket.setSoLinger(boolean, int)`

    - #### getFileDescriptor

          protected FileDescriptor getFileDescriptor()

      Returns the value of this socket's `fd` field.
      Returns:
        the value of this socket's `fd` field.
      See Also:
        `fd`

    - #### getInetAddress

          protected InetAddress getInetAddress()

      Returns the value of this socket's `address` field.
      Returns:
        the value of this socket's `address` field.
      See Also:
        `address`

    - #### getPort

          protected int getPort()

      Returns the value of this socket's `port` field.
      Returns:
        the value of this socket's `port` field.
      See Also:
        `port`

    - #### supportsUrgentData

          protected boolean supportsUrgentData()

      Returns whether or not this SocketImpl supports sending urgent data. By default, false is returned unless the method is overridden in a sub-class
      Returns:
        true if urgent data supported
      Since:
        1.4
      See Also:
        `address`

    - #### sendUrgentData

          protected abstract void sendUrgentData(int data)
                                          throws IOException

      Send one byte of urgent data on the socket. The byte to be sent is the low eight bits of the parameter
      Parameters:
        `data` - The byte of data to send
      Throws:
        `IOException` - if there is an error sending the data.
      Since:
        1.4

    - #### getLocalPort

          protected int getLocalPort()

      Returns the value of this socket's `localport` field.
      Returns:
        the value of this socket's `localport` field.
      See Also:
        `localport`

    - #### toString

          public String toString()

      Returns the address and port of this socket as a `String`.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of this socket.

    - #### setPerformancePreferences

          protected void setPerformancePreferences(int connectionTime,
                                                   int latency,
                                                   int bandwidth)

      Sets performance preferences for this socket.

      Sockets use the TCP/IP protocol by default. Some implementations may offer alternative protocols which have different performance characteristics than TCP/IP. This method allows the application to express its own preferences as to how these tradeoffs should be made when the implementation chooses from the available protocols.

      Performance preferences are described by three integers whose values indicate the relative importance of short connection time, low latency, and high bandwidth. The absolute values of the integers are irrelevant; in order to choose a protocol the values are simply compared, with larger values indicating stronger preferences. Negative values represent a lower priority than positive values. If the application prefers short connection time over both low latency and high bandwidth, for example, then it could invoke this method with the values `(1, 0, 0)`. If the application prefers high bandwidth above low latency, and low latency above short connection time, then it could invoke this method with the values `(0, 1, 2)`. By default, this method does nothing, unless it is overridden in a a sub-class.

      Parameters:
        `connectionTime` - An `int` expressing the relative importance of a short connection time
        `latency` - An `int` expressing the relative importance of low latency
        `bandwidth` - An `int` expressing the relative importance of high bandwidth
      Since:
        1.5

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