Pierre Fernique (Centre de Donnees astronomiques de Stras), Francois Bonnarel (Centre de Donnees astronomiques de Stras)
The applet feature has certainly been the reason of the success of the java language fast development: with a simple mouse-click it became possible to download remote executables and to run them via standard browsers such as Netscape or IExplorer. However, three years after its first release, many java developments are in fact standalone applications which require an installation of the JVM (java virtual machine) rather than applets. In which conditions is the applet feature a really applicable concept ?
This paper presents the CDS (Centre de Donnees astronomiques de Strasbourg) experience of java applets through the development of Aladin java . Aladin is a viewer of astronomical images which has the capability of overlaying sources from catalogs or databases such as Simbad or NED. It has been available since January 1999 among the CDS services at http://aladin.u-strasbg.fr/AladinJava
We present the limitations that we encountered in building the Aladin java applet, and how to overcome them: support of all browser versions, insuring sifficient performances, dealing with the access restrictions on local disks and in particular keeping the code small enough to be easily downloaded. In the specific astronomical context, we discuss the image and catalog managements. We discuss the possibilitie to re-use, or not, existing java packages in a broader java environment.