The Java core API includes a class called java.lang.System from which system dependent operations can be performed. One of the methods of the System class is getProperty(String) which will return a value for some system defined property. Properties can be defined on the command line to configure an application by using the -D flag of the Java interpreter (at least the one in the Sun JDK). But there is also a set of built-in properties that you can depend on being defined in all Java environments. One of those properties is called java.vendor, which defines the name of the vendor of the Java environment running an applet or application. Up until recently, you could use this property to reliably determine the browser your applet was running in. However, with the new trend towards JVMs that you can plug into any browser, such as Sun’s Activator, fetching the value of the java.vendor property will only tell you what JVM you’re running in, not necessarily the browser.