/*

 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/**

 * Provides the classes for implementing networking applications.

 *

 * <p> The java.net package can be roughly divided in two sections:</p>

 * <ul>

 *     <li><p><i>A Low Level API</i>, which deals with the

 *               following abstractions:</p>

 *     <ul>

 *       <li><p><i>Addresses</i>, which are networking identifiers,

 *              like IP addresses.</p></li>

 *       <li><p><i>Sockets</i>, which are basic bidirectional data communication

 *              mechanisms.</p></li>

 *       <li><p><i>Interfaces</i>, which describe network interfaces. </p></li>

 *     </ul></li>

 *     <li> <p><i>A High Level API</i>, which deals with the following

 *          abstractions:</p>

 *     <ul>

 *       <li><p><i>URIs</i>, which represent

 *               Universal Resource Identifiers.</p></li>

 *       <li><p><i>URLs</i>, which represent

 *               Universal Resource Locators.</p></li>

 *       <li><p><i>Connections</i>, which represents connections to the resource

 *               pointed to by <i>URLs</i>.</p></li>

 *       </ul></li>

 * </ul>

 * <h2>Addresses</h2>

 * <p>Addresses are used throughout the java.net APIs as either host

 *    identifiers, or socket endpoint identifiers.</p>

 * <p>The {@link java.net.InetAddress} class is the abstraction representing an

 *    IP (Internet Protocol) address.  It has two subclasses:

 * <ul>

 *       <li>{@link java.net.Inet4Address} for IPv4 addresses.</li>

 *       <li>{@link java.net.Inet6Address} for IPv6 addresses.</li>

 * </ul>

 * <p>But, in most cases, there is no need to deal directly with the subclasses,

 *    as the InetAddress abstraction should cover most of the needed

 *    functionality.</p>

 * <h3><b>About IPv6</b></h3>

 * <p>Not all systems have support for the IPv6 protocol, and while the Java

 *    networking stack will attempt to detect it and use it transparently when

 *    available, it is also possible to disable its use with a system property.

 *    In the case where IPv6 is not available, or explicitly disabled,

 *    Inet6Address are not valid arguments for most networking operations any

 *    more. While methods like {@link java.net.InetAddress#getByName} are

 *    guaranteed not to return an Inet6Address when looking up host names, it

 *    is possible, by passing literals, to create such an object. In which

 *    case, most methods, when called with an Inet6Address will throw an

 *    Exception.</p>

 * <h2>Sockets</h2>

 * <p>Sockets are means to establish a communication link between machines over

 *    the network. The java.net package provides 4 kinds of Sockets:</p>

 * <ul>

 *       <li>{@link java.net.Socket} is a TCP client API, and will typically

 *            be used to {@linkplain java.net.Socket#connect(SocketAddress)

 *            connect} to a remote host.</li>

 *       <li>{@link java.net.ServerSocket} is a TCP server API, and will

 *            typically {@linkplain java.net.ServerSocket#accept accept}

 *            connections from client sockets.</li>

 *       <li>{@link java.net.DatagramSocket} is a UDP endpoint API and is used

 *            to {@linkplain java.net.DatagramSocket#send send} and

 *            {@linkplain java.net.DatagramSocket#receive receive}

 *            {@linkplain java.net.DatagramPacket datagram packets}.</li>

 *       <li>{@link java.net.MulticastSocket} is a subclass of

 *            {@code DatagramSocket} used when dealing with multicast

 *            groups.</li>

 * </ul>

 * <p>Sending and receiving with TCP sockets is done through InputStreams and

 *    OutputStreams which can be obtained via the

 *    {@link java.net.Socket#getInputStream} and

 *    {@link java.net.Socket#getOutputStream} methods.</p>

 * <h2>Interfaces</h2>

 * <p>The {@link java.net.NetworkInterface} class provides APIs to browse and

 *    query all the networking interfaces (e.g. ethernet connection or PPP

 *    endpoint) of the local machine. It is through that class that you can

 *    check if any of the local interfaces is configured to support IPv6.</p>

 * <p>Note, all conforming implementations must support at least one

 *    {@code NetworkInterface} object, which must either be connected to a

 *    network, or be a "loopback" interface that can only communicate with

 *    entities on the same machine.</p>

 *

 * <h2>High level API</h2>

 * <p>A number of classes in the java.net package do provide for a much higher

 *    level of abstraction and allow for easy access to resources on the

 *    network. The classes are:

 * <ul>

 *       <li>{@link java.net.URI} is the class representing a

 *            Universal Resource Identifier, as specified in RFC 2396.

 *            As the name indicates, this is just an Identifier and doesn't

 *            provide directly the means to access the resource.</li>

 *       <li>{@link java.net.URL} is the class representing a

 *            Universal Resource Locator, which is both an older concept for

 *            URIs and a means to access the resources.</li>

 *       <li>{@link java.net.URLConnection} is created from a URL and is the

 *            communication link used to access the resource pointed by the

 *            URL. This abstract class will delegate most of the work to the

 *            underlying protocol handlers like http or https.</li>

 *       <li>{@link java.net.HttpURLConnection} is a subclass of URLConnection

 *            and provides some additional functionalities specific to the

 *            HTTP protocol.</li>

 * </ul>

 * <p>The recommended usage is to use {@link java.net.URI} to identify

 *    resources, then convert it into a {@link java.net.URL} when it is time to

 *    access the resource. From that URL, you can either get the

 *    {@link java.net.URLConnection} for fine control, or get directly the

 *    InputStream.<p>

 * <p>Here is an example:</p>

 * <p><pre>

 * URI uri = new URI("http://java.sun.com/");

 * URL url = uri.toURL();

 * InputStream in = url.openStream();

 * </pre>

 * <h2>Protocol Handlers</h2>

 * As mentioned, URL and URLConnection rely on protocol handlers which must be

 * present, otherwise an Exception is thrown. This is the major difference with

 * URIs which only identify resources, and therefore don't need to have access

 * to the protocol handler. So, while it is possible to create an URI with any

 * kind of protocol scheme (e.g. {@code myproto://myhost.mydomain/resource/}),

 * a similar URL will try to instantiate the handler for the specified protocol;

 * if it doesn't exist an exception will be thrown.

 * <p>By default the protocol handlers are loaded dynamically from the default

 *    location. It is, however, possible to add to the search path by setting

 *    the {@code java.protocol.handler.pkgs} system property. For instance if

 *    it is set to {@code myapp.protocols}, then the URL code will try, in the

 *    case of http, first to load {@code myapp.protocols.http.Handler}, then,

 *    if this fails, {@code http.Handler} from the default location.<p>

 * <p>Note that the Handler class <b>has to</b> be a subclass of the abstract

 *    class {@link java.net.URLStreamHandler}.</p>

 * <h2>Additional Specification</h2>

 * <ul>

 *       <li><a href="doc-files/net-properties.html">

 *            Networking System Properties</a></li>

 * </ul>

 *

 * @since JDK1.0

 */

package java.net;