Support of HTTPS through Java Secure Socket Extension (JSSE) rather than the browser
Enhanced applet caching so that other files, such as GIF, JPEG, and AU, can be cached in addition to JAR and class files
Applet persistence across browser page changes
Various applet-compatibility enhancements to allow most JDK 1.1 applets to run seemlessly in Java 2.
Access to the DOM through standard, w3c-defined interfaces
Assertion and logging support
Applet usability enhancements that include a customizable progress bar for applet loading
Enhanced options in the Java Console to allow dynamic reconfiguration of proxy settings, the policy file, etc., while the applet is running.
For more information, see http://java.sun.com/j2se/1.4/docs/guide/plugin/index.html.