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HighScore class stores and protects access to the user's
high score for ExampleGame (and any other games that call it).
For simplicity, this class saves
the high score value into a file, called .highscore, in the
user's home directory. However, before allowing ExampleGame to
retrieve or update the user's high score value, this class
checks to make sure that the user has granted ExampleGame
permission to access the high score in his/her security
policy file.
ExampleGame has the HighScorePermissionExampleGame has permission to access
the user's high score, the HighScore class must:
System.getSecurityManager() to get
the currently installed security manager.
HighScorePermission object, and
checkPermission
method, and pass it the newly constructed HighScorePermission object.
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(new HighScorePermission(gameName));
}
checkPermission method essentially
asks the security manager
if ExampleGame has the specified HighScorePermission.
In other words, it asks
the security manager if ExampleGame has permission to update the user's
high score value for the specified game (ExampleGame).
The underlying security framework will consult
the user's security policy to see if ExampleGame indeed has this
permission.
Here
is the complete source code for the HighScore class.
Note: The doPrivileged method calls are used to enable
HighScore to temporarily access resources that are
available to it
but that are not available to the code that calls it (ExampleGame).
For example, it is expected that the policy file will
grant HighScore permission to access the .highscore
file in the user's home directory, but it will not grant this permission
to games, such as ExampleGame.
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