Applications and Applets

There are two types of Java programs: applications and applets. An application is executed by a JVM running directly on the system. An applet is typically executed by a web browser. The browser contains a JVM and also provides the environment in which the applet runs.

When a user opens a web page containing a reference to an applet, the applet is downloaded to a user’s machine. It is essential to restrict the capabilities of these applets. If, for example, an applet can read and write files on the local machine, it can accidentally or deliberately corrupt or erase important information. Therefore, applets execute within a “sandbox.” They are blocked from reading and writing files. Other restrictions also apply This is an important part of the Java security architecture.

It is possible to associate a digital signature with an applet. This indicates that the applet was developed by a specific individual or organization. A user can configure his or her browser to trust applets from certain sources. The constraints of the “sandbox” can then be relaxed for these programs.