Java How to Program Fourth Edition - DCC

Chapter 17 Networking 1061
• The HTTP protocol (Hypertext Transfer Protocol) that forms the basis of the World Wide Web
uses URIs (Uniform Resource Identifiers, also called URLs or Uniform Resource Locators) to locate
data on the Internet. Common URIs represent files or directories and can represent complex
tasks such as database lookups and Internet searches.
• Web browsers often restrict an applet so that it can communicate only with the machine from
which it was originally downloaded.
• A Hashtable stores key/value pairs. A program uses a key to store and retrieve an associated
value in the Hashtable. Hashtable method put takes two arguments—a key and its associated
value—and places the value in the Hashtable at a location determined by the key. Hashtable
method get takes one argument—a key—and retrieves the value (as an Object
reference) associated with the key.
• A Vector is a dynamically resizable array of Objects. Vector method addElement adds
a new element to the end of the Vector.
• Applet method getAppletContext returns a reference to an AppletContext object that
represents the applet’s environment (i.e., the browser in which the applet is executing).
• AppletContext method showDocument receives a URL object as an argument and passes it
to the AppletContext (i.e., the browser), which displays the World Wide Web resource associated
with that URL.
• A second version of AppletContext method showDocument enables an applet to specify the
target frame in which Web resource should be displayed. Special target frames include _blank
(display the content from the specified URI in a new Web browser window), _self (display the
content from the specified URI in the same frame as the applet) and _top (the browser should
remove the current frames, then display the content from the specified URI in the current window).
• Component method setCursor changes the mouse cursor when the cursor is positioned over
a specific GUI component. The Cursor constructor receives an integer indicating the cursor type
(such as Cursor.WAIT_CURSOR or Cursor.DEFAULT_CURSOR).
• JEditorPane method setPage downloads the document specified by its argument and displays
it in the JEditorPane.
• Typically, an HTML document contains hyperlinks—text, images or GUI components that, when
clicked, link to another document on the Web. If an HTML document is displayed in a JEditor-
Pane and the user clicks a hyperlink, the JEditorPane generates a HyperlinkEvent
(package javax.swing.event) and notifies all registered HyperlinkListeners (package
javax.swing.event) of that event.
• HyperlinkEvent method getEventType determines the type of the HyperlinkEvent.
Class HyperlinkEvent contains public static inner class EventType, which defines
three hyperlink event types: ACTIVATED (user clicked a hyperlink), ENTERED (user moved the
mouse over a hyperlink) and EXITED (user moved the mouse away from a hyperlink).
• HyperlinkEvent method getURL obtains the URL represented by the hyperlink.
• Stream-based connections are managed with Socket objects.
• AServerSocket object establishes the port where a server waits for connections from clients.
The second argument to the ServerSocket constructor specifies the number of clients that can
wait for a connection and be processed by the server. If the queue of clients is full, client connections
are refused. The ServerSocket method accept waits indefinitely (i.e., blocks) for a
connection from a client and returns a Socket object when a connection is established.
• Socket method getOutputStream gets a reference to the OutputStream associated with
a Socket. Socket method getInputStream gets a reference to the InputStream associated
with the Socket.