Java 2 Standard Edition (J2SE) 5.0 Release 4 delivers improved reliability and compatibility for Java 2 Platform Standard Edition 5.0 on Mac OS X v10.4.5 and later. This release includes J2SE version 1.5.0_06. With this update J2SE 5.0 becomes the preferred Java version, superseding Java 1.4.2. Java 1.4.2 is still installed on your machine, but applications will run with J2SE 5.0 unless they specifically request Java 1.4.2.
For more details on this Update, please visit this website: http://docs.info.apple.com/article.html?artnum=302983