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Java in a Nutshell

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28. The java.net Package

The java.net package provides a powerful and flexible infrastructure for networking. Figure 28.1 shows the class hierarchy for this package. Many of the classes in this package are part of the networking infrastructure and are not used by normal applications; these complicated classes can make the package a difficult one to understand. In this overview we describe only the classes that an application might normally use.

The URL class represents an Internet Uniform Resource Locator. It provides a very simple interface to networking--the object referred to by the URL can be downloaded with a single call, or streams may be opened to read from or write to the object.

At a slightly more complex level, the URLConnection object may be obtained from a given URL object. The URLConnection class provides additional methods that allow you to work with URLs in more sophisticated ways.

If you want to do more than simply download an object referenced by a URL, you can do your own networking with the Socket class. This class allows you to connect to a specified port on a specified Internet host and read and write data using the InputStream and OutputStream classes of the java.io package. If you want to implement a server to accept connections from clients, you can use the related ServerSocket class. Both Socket and ServerSocket use the InetAddress address class, which represents an Internet address.

The java.net package allows you to do low-level networking with DatagramPacket objects which may be sent and received over the network through a DatagramSocket object. In Java 1.1, the package has been extended to include a MulticastSocket class that supports multicast networking.

28.1 java.net.BindException (JDK 1.1)

This exception signals that a socket could not be bound to a local address and port. This often means that the port is already in use.

public class BindException extends SocketException {
    // Public Constructors
            public BindException(String msg);
            public BindException();



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