OOP Lab Task 5 - Revizia istoricului

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@@ Linia 36: / Linia 36: @@
 #** After you finish with sending messages don't forget to close the output stream of the '''ClientPeer''' object, the input stream and the socket! To be sure that they are closed in any circumstances, put the statements that closes them in a '''finally''' block, atached to a '''try''' block that encloses the other part of the '''main''' method. Be careful, the references used inside the '''finally''' block must be declared outside the '''try''' block and initialized with some value (the initialization value may be null).!
 #** Because the '''run''' method operates with sockets and streams it may also raise checked exceptions of type '''IOException'''. You do not catch them; simply declare that the method '''run''' throws them out.
-# The '''main''' method instantiates a '''Client''' object with some destination IP address (try first with 127.0.0.1), and port 9000 (that connects the client's socket to the destination's socket, the localhost (127.0.0.1) on port 9000), and calls the method '''run''' for the newly created '''Client''' object.
+#* The '''main''' method instantiates a '''Client''' object with some destination IP address (try first with 127.0.0.1), and port 9000 (that connects the client's socket to the destination's socket, the localhost (127.0.0.1) on port 9000), and calls the method '''run''' for the newly created '''Client''' object.
-#* Because both the '''Client''' constructor and the '''run''' method may generate checked exceptions, throw them further outside the '''main''' method.
+#** Because both the '''Client''' constructor and the '''run''' method may generate checked exceptions, throw them further outside the '''main''' method.
-# You may run this file, to see that it compiles, builds and runs, but the execution will end abruptly with an exception because there is still no server running, to which your client might connect (Connection refused). The following steps are devoted to the other part of the connection, the receiver of messages, which also acts as the server.
+# You may run the '''Client''' class, to see that it compiles, builds and runs, but the execution will end abruptly with an exception because there is still no server running, to which your client might connect (Connection refused). The following steps are devoted to the other part of the connection, the receiver of messages, which also acts as the server.
 # Add to the '''labutil''' package a class called <code style="color:green;">ServerPeer</code> with the following features:
 #* The constructor has as its sole argument a reference to a pre-initialized '''Socket''' object, that it stores in a private field.

@@ Linia 27: / Linia 27: @@
 # Add to the '''labutil''' package another class, named <code style="color:green;">Client</code>, which is executable (has a '''main''' method). This class has
 #* A constructor, with two arguments, a string for an internet address, and an integer for a port number. This constructor creates a '''Socket''' object and connects it to the desired remote socket, whose address and port are given as arguments.
 #* A method named <code style="color:green;">run</code>, without arguments, which does the following:
-#* First, it instantiates a '''ClientPeer''' object with your name as an argument (you are the sender!) and the reference to the '''Socket''' object as the other argument.
+#** First, it instantiates a '''ClientPeer''' object with your name as an argument (you are the sender!) and the reference to the '''Socket''' object as the other argument.
-#* After that, open an input stream of characters to read from the keyboard. The input stream from the keyboard is already enclosed in the object '''System.in''', which is opened and available by default. However, this stream is a byte stream, therefore you need to filter it properly, so that the bytes are transformed to characters. To do that, you enclose the '''System.in''' stream into an <code style="color:green;">InputStreamReader</code> object. The '''Reader''' object ('''InputStreamReader''' is derived from '''Reader''') delivers the stream character by character. To read a whole line from the keyboard without calling the '''read''' method for each character, you enclose further the '''InputStreamReader''' into a <code style="color:green;">BufferedReader</code> object, whose '''readLine''' method fits this purpose. The '''readLine''' method returns (with a string) only after you type the ''Enter'' key (but the newline character will not be part of the returned string).
+#** After that, open an input stream of characters to read from the keyboard. The input stream from the keyboard is already enclosed in the object '''System.in''', which is opened and available by default. However, this stream is a byte stream, therefore you need to filter it properly, so that the bytes are transformed to characters. To do that, you enclose the '''System.in''' stream into an <code style="color:green;">InputStreamReader</code> object. The '''Reader''' object ('''InputStreamReader''' is derived from '''Reader''') delivers the stream character by character. To read a whole line from the keyboard without calling the '''read''' method for each character, you enclose further the '''InputStreamReader''' into a <code style="color:green;">BufferedReader</code> object, whose '''readLine''' method fits this purpose. The '''readLine''' method returns (with a string) only after you type the ''Enter'' key (but the newline character will not be part of the returned string).
-#* Then, read a string of characters from the keyboard (from the previously opened input stream) and call the '''sendMessage''' method of the '''ClientPeer''' object. Your typed messages will thus be sent to the destination.
+#** Then, read a string of characters from the keyboard (from the previously opened input stream) and call the '''sendMessage''' method of the '''ClientPeer''' object. Your typed messages will thus be sent to the destination.
-#* You may send messages in a continuous loop (type a line, press ''Enter'', type another line, press ''Enter'' a.s.o).
+#** You may send messages in a continuous loop (type a line, press ''Enter'', type another line, press ''Enter'' a.s.o).
-#* To break the loop, you test for a special typed line, ''QUIT'' (it will act like a command, not a message to be sent). Remember how to check that two strings are equal!
+#** To break the loop, you test for a special typed line, ''QUIT'' (it will act like a command, not a message to be sent). Remember how to check that two strings are equal!
-#* After you finish with sending messages don't forget to close the output stream of the '''ClientPeer''' object, the input stream and the socket! To be sure that they are closed in any circumstances, put the statements that closes them in a '''finally''' block, atached to a '''try''' block that encloses the other part of the '''main''' method. Be careful, the references used inside the '''finally''' block must be declared outside the '''try''' block and initialized with some value (the initialization value may be null).!
+#** After you finish with sending messages don't forget to close the output stream of the '''ClientPeer''' object, the input stream and the socket! To be sure that they are closed in any circumstances, put the statements that closes them in a '''finally''' block, atached to a '''try''' block that encloses the other part of the '''main''' method. Be careful, the references used inside the '''finally''' block must be declared outside the '''try''' block and initialized with some value (the initialization value may be null).!
-#* Because the '''run''' method operates with sockets and streams it may also raise checked exceptions of type '''IOException'''. You do not catch them; simply declare that the method '''run''' throws them out.
+#** Because the '''run''' method operates with sockets and streams it may also raise checked exceptions of type '''IOException'''. You do not catch them; simply declare that the method '''run''' throws them out.
 # The '''main''' method instantiates a '''Client''' object with some destination IP address (try first with 127.0.0.1), and port 9000 (that connects the client's socket to the destination's socket, the localhost (127.0.0.1) on port 9000), and calls the method '''run''' for the newly created '''Client''' object.
 #* Because both the '''Client''' constructor and the '''run''' method may generate checked exceptions, throw them further outside the '''main''' method.

@@ Linia 62: / Linia 62: @@
 # How to test your classes? Actually you have two separate applications, a server and a client. You have just started the server, but it runs without end waiting for a client to send messages. You need to start separately a client. To do that, switch the editor window to Client.java and run that file too (right-click and select ''Run File'', or bla bla). A second output tab appears. You have now two programs running at the same time, with their outputs displayed on separate tabs in the output window at the bottom of the NetBeans environment.
 # Type something in the output window of the Client and press ''Enter''. Look to the other tab and see that the Sever outputs the message you have just typed. Try with other messages. To close the Client, type ''QUIT'' and press ''Enter''. Depending on how you have written the '''run''' method of the '''Server''' class, the server will end too, or it will continue, listening for other clients to connect (in which case you run again the Client.java, type something a.s.o)
-# If you want more fun, and know the IP address of the computer of your colleague, ask him to open a server, change your '''Client''' class to open a Socket with that IP instead of the localhost IP 127.0.0.1, and run locally a client. Please, send only peacefull messages!
+# If you want more fun, and know the IP address of the computer of your colleague, ask him to open a server on some port, change your '''Client''' class to open a Socket with that IP instead of the localhost IP 127.0.0.1, and the desired port, then run locally your client and type messages for your colleague. Please, send him only peacefull messages!
 == Submitting ==

@@ Linia 61: / Linia 61: @@
 # Run the Server class (with the Server.java opened in the editor window right-click and select ''Run File'', or click ''Run''->''Run File'' from the general Menu). If there are no errors the program runs, but nothing is output, and it appears to run without end. It's because there are no clients running around and it listens continuously waiting for some client to appear (the '''accept''' method returns only after it catches a client, or something bad happens).
 # How to test your classes? Actually you have two separate applications, a server and a client. You have just started the server, but it runs without end waiting for a client to send messages. You need to start separately a client. To do that, switch the editor window to Client.java and run that file too (right-click and select ''Run File'', or bla bla). A second output tab appears. You have now two programs running at the same time, with their outputs displayed on separate tabs in the output window at the bottom of the NetBeans environment.
-# Type something in the output window of the Client and press ''Enter''. Look to the other tab and see that the Sever outputs the message you have just typed. Try with other messages. To close the Client, type ''QUIT'' and press ''Enter''. Depending on how you have written the '''run''' method of the '''Server''' class, the server will end too, or it will continue, listening for other clients to connect (in case which you run again the Client.java, type something a.s.o)
+# Type something in the output window of the Client and press ''Enter''. Look to the other tab and see that the Sever outputs the message you have just typed. Try with other messages. To close the Client, type ''QUIT'' and press ''Enter''. Depending on how you have written the '''run''' method of the '''Server''' class, the server will end too, or it will continue, listening for other clients to connect (in which case you run again the Client.java, type something a.s.o)
 # If you want more fun, and know the IP address of the computer of your colleague, ask him to open a server, change your '''Client''' class to open a Socket with that IP instead of the localhost IP 127.0.0.1, and run locally a client. Please, send only peacefull messages!

@@ Linia 61: / Linia 61: @@
 # Run the Server class (with the Server.java opened in the editor window right-click and select ''Run File'', or click ''Run''->''Run File'' from the general Menu). If there are no errors the program runs, but nothing is output, and it appears to run without end. It's because there are no clients running around and it listens continuously waiting for some client to appear (the '''accept''' method returns only after it catches a client, or something bad happens).
 # How to test your classes? Actually you have two separate applications, a server and a client. You have just started the server, but it runs without end waiting for a client to send messages. You need to start separately a client. To do that, switch the editor window to Client.java and run that file too (right-click and select ''Run File'', or bla bla). A second output tab appears. You have now two programs running at the same time, with their outputs displayed on separate tabs in the output window at the bottom of the NetBeans environment.
-# Type something in the output window of the Client and press ''Enter''. Look to the other tab and see that the Sever outputs the message you have just typed. Try with other messages. To close the Client, type ''QUIT'' and press ''Enter''. Depending on how you have written the '''main''' of the '''Server''' class, the server will end too, or it will continue, listening for other clients to connect (in case which you run again the Client.java, type something a.s.o)
+# Type something in the output window of the Client and press ''Enter''. Look to the other tab and see that the Sever outputs the message you have just typed. Try with other messages. To close the Client, type ''QUIT'' and press ''Enter''. Depending on how you have written the '''run''' method of the '''Server''' class, the server will end too, or it will continue, listening for other clients to connect (in case which you run again the Client.java, type something a.s.o)
 # If you want more fun, and know the IP address of the computer of your colleague, ask him to open a server, change your '''Client''' class to open a Socket with that IP instead of the localhost IP 127.0.0.1, and run locally a client. Please, send only peacefull messages!

@@ Linia 48: / Linia 48: @@
 #** As long as the connection is open, the '''readObject method''' waits for a complete object to be received from the stream and then returns with a reference to it. If the connection is closed (by the other side for example) the method aborts and throws the '''EOFException'''. Use this exception to neatly end the read loop. For this purpose, enclose the continuous loop in a '''try''' block and attach a '''catch''' for this particular exception, whithout statements. This catch will simply serve to continue the program, instead of aborting it with an exception. If you want a more realistic output, you may print on the screen, after the '''EOFException''' was caught, the message ''The client has disconnected.'' or something like that.
 #** Don't forget to close everything after the connection is closed (and you exited from the loop). You have just added a '''try''' block, so you need only to attach to it the '''finally''' block with statements to close the input stream and the socket. Be careful, the references used inside the '''finally''' block must be declared ouside the '''try''' block!
-# The last to be added to your package is a class called <code style="color:green;">Server</code>, which is executable (has a main method).
+# The last to be added to your package is a class called <code style="color:green;">Server</code>, which is executable (has a main method). It encloses:
-#* The main method instantiates a '''ServerSocket''' object attached to port 9000.
+#* One constructor, with a single argument which is the public port number of your server. This constructor instantiates a '''ServerSocket''' object connected the given port.
-#* The '''ServerSocket''' method '''accept''' is used to listen for clients. This method returns after a client request is accepted and a connection with that client is established. The method returns a reference to a '''Socket''' object created specially for this connection. You use this '''Socket''' reference to instantiate a '''ServerPeer''' object.
+#** The '''ServerSocket''' reference must be an instance field, so that it may be used by the other methods of this class.
-#* Call then the '''run''' method for this newly created '''ServerPeer''' object.
+#* A method, named <code style="color:green;">void run()</code>, without arguments, which:
-#* The method '''run''' returns after the connection is closed (remember, you just added the proper '''try'''-'''catch''' construction to handle the '''EOFException'''. The '''Socket''' is closed, but not the '''ServerSocket'''. You may call again the '''accept''' method to accept another client, a.s.o.
+#** calls the '''ServerSocket''''s method '''accept''', to listen for clients. This method returns after a client request is accepted and a connection with that client is established. The method returns a reference to a local '''Socket''' object created specifically for this connection. You use this '''Socket''' reference to instantiate a '''ServerPeer''' object.
-#* Don't forget to close the '''SeverSocket''' object after you decide to no longer accept clients and to exit your program.
+#** calls next the '''run''' method for this newly created '''ServerPeer''' object.
-#* If it still has compilation errors it's because you forget about that annoying exceptions. The '''main''' method uses various sockets and streams, that may throw exceptions ... already a classic story. Don't bother with them, simply append the necessary declaration to the '''main''' method signature. In addition to '''IOException'''s, a '''ClassNotFoundException''' may be thrown from '''run''', so it needs to be declared too.
+#** both the '''accept''' method and the '''run''' method of the '''ServerPeer''' may generate exceptions. You do not handle them, but they must be declared as thrown by the method.
 # Run the Server class (with the Server.java opened in the editor window right-click and select ''Run File'', or click ''Run''->''Run File'' from the general Menu). If there are no errors the program runs, but nothing is output, and it appears to run without end. It's because there are no clients running around and it listens continuously waiting for some client to appear (the '''accept''' method returns only after it catches a client, or something bad happens).
 # How to test your classes? Actually you have two separate applications, a server and a client. You have just started the server, but it runs without end waiting for a client to send messages. You need to start separately a client. To do that, switch the editor window to Client.java and run that file too (right-click and select ''Run File'', or bla bla). A second output tab appears. You have now two programs running at the same time, with their outputs displayed on separate tabs in the output window at the bottom of the NetBeans environment.

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 #** The object is sent through the output stream of the Socket. You get the reference to that stream using the Socket's method <code style="color:green;">getOutputStream</code>, but to be able to send objects through this stream, which is only a basic stream of bytes, you need to enclose it in a filter stream of type <code style="color:green;">ObjectOutputStream</code> (this object does the serialization for you, that is it converts the '''Message''' object into a stream of bytes).
 #* A method named <code style="color:green;">close</code>, without arguments and return values, that symply closes the output stream.
-#** The output stream is created at '''ClientPeer''' instantiation, used by '''sendMessage''' method which writes '''Message''' objects into, and closed by '''close''' method.
+#* The output stream is created at '''ClientPeer''' instantiation, used by '''sendMessage''' method which writes '''Message''' objects into, and closed by '''close''' method.
-#** The constructor and both methods employ a socket and a stream, whose methods may throw various exceptions of type '''IOException''' when called. You do not catch them, but, because they are checked exceptions, you must declare them to be thrown by the constructor and the methods.
+#* The constructor and both methods employ a socket and a stream, whose methods may throw various exceptions of type '''IOException''' when called. You do not catch them, but, because they are checked exceptions, you must declare them to be thrown by the constructor and the methods.
-#* All fields must be private.
+# All fields must be private.
 # Add to your project another class, named <code style="color:green;">Client</code>, which is executable (has a '''main''' method).
 #* First, the '''main''' method instantiates a '''Socket''' object with the destination IP address 127.0.0.1 and port 9000 (that connects the client's socket to the destination's socket, the localhost (127.0.0.1) on port 9000).

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 #* Only one constructor, that takes as arguments a string (the user/sender name) and a reference to a '''Socket''' object, that is supposed to be already instantiated and connected, and saves them in private fields.
 #* A method <code style="color:green;">void sendMessage(String message)</code>, that creates a '''Message''' object with the content taken from the method's argument and the sender's name read from the class' fields, and sends the newly created object through the available Socket.
-#** In order to be able to send a '''Message''' object through a stream (to serialize that object), it must be serializable.
+#** In order to be able to send a '''Message''' object through a stream (to serialize that object), that object must be serializable.
 #** The object is sent through the output stream of the Socket. You get the reference to that stream using the Socket's method <code style="color:green;">getOutputStream</code>, but to be able to send objects through this stream, which is only a basic stream of bytes, you need to enclose it in a filter stream of type <code style="color:green;">ObjectOutputStream</code> (this object does the serialization for you, that is it converts the '''Message''' object into a stream of bytes).
 #* A method named <code style="color:green;">close</code>, without arguments and return values, that symply closes the output stream.