Firewalls essentially partition the Java Card platform's object system into separate protected object spaces called contexts. These are illustrated in FIGURE 6-1. The firewall is the boundary between one context and another. The Java Card RE shall allocate and manage a context for each Java API package containing applets<SUP>[1]</SUP>. All applet instances within a single Java API package share the same context. There is no firewall between individual applet instances within the same package. That is, an applet instance can freely access objects belonging to another applet instance that resides in the same package.

FIGURE 6-1 Contexts Within the Java Card Platform's Object System

In addition, the Java Card RE maintains its own Java Card RE context. This context is much like the context of an applet, but it has special system privileges so that it can perform operations that are denied to contexts of applets. For example, access from the Java Card RE context to any applet instance's context is allowed, but the converse, access from an applet instance's context to the Java Card RE context, is prohibited by the firewall.