ch19.htm

对于程序员来说可以利用JAVA来开发网络游戏！

object to get the game underway. The <TT><FONT FACE="Courier">closeConnections</FONT></TT>
method closes the client connection and is typically used to end
the game.
<P>
The last class the NetConnect4 server comprises is the <TT><FONT FACE="Courier">Game</FONT></TT>
class, which handles the details associated with managing the
game logic and the communication between players. The <TT><FONT FACE="Courier">Game</FONT></TT>
class takes on the bulk of the work involved in maintaining the
state of the game, as well as communicating that state between
the players. The <TT><FONT FACE="Courier">Game</FONT></TT> class
contains a group of member constants that define the different
states in the game:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">public static final int ERROR = -1;<BR>
public static final int IWON = -2;<BR>
public static final int IQUIT = -3;<BR>
public static final int ITIED = -4;<BR>
public static final int YOURTURN = -5;<BR>
public static final int SENTSTRING = -6;</FONT></TT>
</BLOCKQUOTE>
<P>
Along with the constants, the <TT><FONT FACE="Courier">Game</FONT></TT>
class has member variables representing each player, along with
an event queue for each player and a string used to send messages
to the other player:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">private Connect4Player&nbsp;&nbsp;player1
= null;<BR>
private Connect4Player&nbsp;&nbsp;player2 = null;<BR>
private Vector&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;p1Queue
= null;<BR>
private Vector&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;p2Queue
= null;<BR>
private String&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString;</FONT></TT>
</BLOCKQUOTE>
<P>
An <I>event queue</I> is a list of events that take place within
a particular context.
<P>
In the case of NetConnect4, an event consists of player moves
and related game states. So the event queue is used to keep up
with the latest player moves and game states.
<P>
The workhorse method in the <TT><FONT FACE="Courier">Game</FONT></TT>
class is <TT><FONT FACE="Courier">playGame</FONT></TT>, which
essentially manages the game flow and logic for each player. Listing
19.3 contains the source code for the <TT><FONT FACE="Courier">playGame</FONT></TT>
method.
<HR>
<BLOCKQUOTE>
<B>Listing 19.3. The </B><TT><B><FONT FACE="Courier">Game</FONT></B></TT><B>
class's </B><TT><B><FONT FACE="Courier">playGame</FONT></B></TT><B>
method.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">public void playGame(Connect4Player me)
{<BR>
&nbsp;&nbsp;String instr;<BR>
&nbsp;&nbsp;boolean playgame = true;<BR>
&nbsp;&nbsp;boolean theirturn = false;<BR>
<BR>
&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;if (me == player2) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theirturn = true;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;else if (me != player1) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Illegal
call to playGame!&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;while (playgame) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (!theirturn) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;YOURTURN&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;instr = me.receive();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;instr = instr.toUpperCase();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;instr = instr.trim();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (instr.startsWith(&quot;IQUIT&quot;))
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
IQUIT);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (instr.startsWith(&quot;IWON&quot;))
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= me.receive();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= sentString.toUpperCase();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= sentString.trim();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
IWON);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
SENTSTRING);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (instr.startsWith(&quot;ITIED&quot;))
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= me.receive();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= sentString.toUpperCase();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= sentString.trim();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
ITIED);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
SENTSTRING);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sentString
= instr;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,
SENTSTRING);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theirturn = false;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (playgame) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;THEIRTURN&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int stat = getStatus(me);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (stat == IWON)
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;THEYWON&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
(getStatus(me) != SENTSTRING) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Received
Bad Status&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.closeConnections();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(sentString);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (stat
== ITIED) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;THEYTIED&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
(getStatus(me) != SENTSTRING) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Received
Bad Status&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.closeConnections();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(sentString);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (stat
== IQUIT) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;THEYQUIT&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (stat
== SENTSTRING) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(sentString);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (stat
== ERROR) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.send(&quot;ERROR&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.closeConnections();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Received
Bad Status&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendStatus(me,ERROR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;me.closeConnections();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;playgame
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;me.closeConnections();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;return;<BR>
&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;catch (IOException e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;I/O Error: &quot;
+ e);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;System.exit(1);<BR>
&nbsp;&nbsp;}<BR>
}</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
The logic used in <TT><FONT FACE="Courier">playGame</FONT></TT>
is fairly simple in that it models the way a game of Connect4
takes place; basically, each player waits while the other takes
her turn. The only potentially confusing aspect of <TT><FONT FACE="Courier">playGame</FONT></TT>
is the mechanism it uses to communicate between the players. Each
player has an event queue, which contains game information sent
by the other player. The players communicate with each other in
an indirect fashion by using the event queue. The state of the
game is encoded into event messages using the state constants,
along with strings. The <TT><FONT FACE="Courier">playGame</FONT></TT>
method interprets this information for each player.
<P>
The <TT><FONT FACE="Courier">getStatus</FONT></TT> method gets
the status of the game for the player passed in the <TT><FONT FACE="Courier">me</FONT></TT>
parameter. Listing 19.4 contains the source code for the <TT><FONT FACE="Courier">getStatus</FONT></TT>
method.
<HR>
<BLOCKQUOTE>
<B>Listing 19.4. The </B><TT><B><FONT FACE="Courier">Game</FONT></B></TT><B>
class's </B><TT><B><FONT FACE="Courier">getStatus</FONT></B></TT><B>
method.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">private synchronized int getStatus(Connect4Player
me) {<BR>
&nbsp;&nbsp;Vector ourVector = ((me == player1) ? p1Queue : p2Queue);
<BR>
&nbsp;&nbsp;while (ourVector.isEmpty()) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;wait();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;catch (InterruptedException e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Error:
&quot; + e);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;Integer retval = (Integer)(ourVector.firstElement());
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ourVector.removeElementAt(0);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;catch (ArrayIndexOutOfBoundsException
e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Array
index out of bounds: &quot; + e);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.exit(1);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;return retval.intValue();<BR>
&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;catch (NoSuchElementException e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Couldn't get
first element: &quot; + e);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;System.exit(1);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;return 0; // never reached, just there
to appease compiler<BR>
&nbsp;&nbsp;}<BR>
}</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
The <TT><FONT FACE="Courier">getStatus</FONT></TT> method waits
until the player's event queue contains status information, and
then it grabs the information and returns it.
<P>
The <TT><FONT FACE="Courier">sendStatus</FONT></TT> method is
the complement of <TT><FONT FACE="Courier">getStatus</FONT></TT>;
it's used to update a player's event queue with status information:
<BLOCKQUOTE>