Java SE 6 features

Scripting Language Support.Generic API for tight integration with scripting languages, and built-in Mozilla JavaScript Rhino integration
JDBC 4.0 API
Java Compiler API
Pluggable Annotations
Native PKI, Java GSS, Kerberos and LDAP support.
Integrated Web Services.Improved Web Service support through JAX-WS (JSR 224)
Lot more enhancements.
integration of SwingWorker in the API
Upgrade of JAXB to version 2.0: Including integration of a StAX parser.
Java Compiler API (JSR 199): an API allowing a Java program to select and invoke a Java Compiler programmatically.
JVM improvements include: synchronization and compiler performance optimizations, new algorithms and upgrades to existing garbage collection algorithms, and application start-up performance
how threads interact through memory.