Server-Class Machine Detection
Improved Support for Environment Variables
JavaBeans Component Architecture
Java API for XML Processing (JAXP)
Remote Method Invocation (RMI)
Java Database Connectivity (JDBC)
Java Naming and Directory Interface (JNDI)
Java Virtual Machine Tool Interface (JVMTI)
Java Platform Debugger Architecture (JPDA)
Annotation Processing Tool (apt)
For a synopsis of performance enhancements, see Performance Enhancements at http://java.sun.com/j2se/1.5.0/docs/guide/performance/speed.html.