"I'm really excited about Mustang," said JavaOne attendee Svein Ove Olafsen, a system developer at Selvaag BlueThink. Mustang's improvements in graphics and performance are of particular interest, Olafsen said.

With Mustang, Sun is seeking lots of feedback form the community at large and is focused on bug fixes. "There are several thousand bug fixes in Mustang but I want you to know that we are very paranoid in fixing bugs," Hamilton said. Identifying potential regressions is a one particular area of concern, he said.

Also planned for Mustang is support for the Java Specification Request (JSR) 199 Compiler API, featuring a service provider API allowing a Java program to select and invoke a Java compiler programmatically.

A second beta of Mustang is due in June.

The Dolphin release, also known as Java SE 7, is set to feature direct support for XML and "super packages," which are new constructs that allow hierarchical modular organization. Super packages are expected to benefit larger scale development.