JPDA itself has many new features, described in more detail on the JPDA enhancements page.
A read-only subset of JDI has been defined. This subset can be used on a debuggee in which no debug code can be executed (such as a core file or a process that is hung or was not started in debug mode). The subset allows creation of JDI connectors for use in debugging such debuggees.
A service provider interface for connectors and transports allows debugger vendors, or even end users, to create their own JDI connectors and transports and plug them into the JPDA reference implementation. For example, a connector could be provided to use SSL to communicate between the debugger and debuggee.
JDI supports the new language features (generics, enums, and varargs).
The lowest layer of JPDA, the Java Virtual Machine Debugger Interface (JVMDI), has been deprecated and will be removed in the next major J2SE release. Replacing it is the Java Virtual Machine Tool Interface (JVMTI). This is a more general interface that allows profiling to be done as well as debugging. The current profiling interface, Java Virtual Machine Profiling Interface(JVMPI) is also deprecated and will be removed in the next major release.
The JPDA reference implementation includes new JDI connectors that allow corefiles and hung processes to be debugged.
Refer to the documentation at http://java.sun.com/j2se/1.5.0/docs/guide/jpda/index.html.