A Java class that allows applications to implement a security policy. 

Usually, the JavaSecurityManager becomes visible when it denies access to a resource like local files:
 java.security.Access''''''Control''''''Exception: access denied (java.io.File''''''Permission /foo.xml read) 
    at java.security.Access''''''Control''''''Context.check''''''Permission(Access''''''Control''''''Context.java:269)
    at java.security.Access''''''Controller.checkPermission(Access''''''Controller.java:401)
    at java.lang.Security''''''Manager.checkPermission(Security''''''Manager.java:524)
    at java.lang.Security''''''Manager.checkRead(Security''''''Manager.java:863)
    at java.io.File.exists(File.java:678)
    at com.badguys.Bad''''''Code$Bad''''''Thread.run(Bad''''''Code.java:32)

However, the most common example can be seen with Java applets which are prevented from:
	* accessing the file system
	* making network connections (for the most part)
	* creating new processes
	* creating class loaders

If there is a security manager in place, the following operations will be checked:

	* Accept a socket connection from a specified host and port number
	* Modify a thread (change its priority, stop it, and so on)
	* Open a socket connection to a specified host and port number
	* Create a new class loader
	* Delete a specified file
	* Create a new process
	* Cause the application to exit
	* Load a dynamic library that contains native methods
	* Wait for a connection on a specified local port number
	* Load a class from a specified package (used by class loaders)
	* Add a new class to a specified package (used by class loaders)
	* Access or modify system properties
	* Access a specified system property
	* Read from a specified file
	* Write to a specified file

Java applications, by default, won't use a security manager unless a ''policy file'' has been specified at the time of application launch. To specify a java policy read up on the following syntax:

 java -Djava.security.manager -Djava.security.policy=someURL SomeApp

The system policy file is by default located at ''' ''java.home''/lib/security/java.policy'''

see more at: http://java.sun.com/j2se/1.4.2/docs/guide/security/PolicyFiles.html

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An attempt to implement something similar in the RubyLanguage is being made in the SecuredRuby project.

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Is there something similar in Smalltalk?

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contributors: AnonymousDonor''''''s, EricHerman