Java HotSpot Client Virtual Machine

The HotSpot Client VM serves as a replacement for both the "classic" and the JIT com- pilers that were used in previous SDK's. The HotSpot Client VM uses the previously mentioned HotSpot technology developed by Sun. The Client- and the Server VM are very similar except that the Client VM has been tuned especially for faster startup times, which makes it more suitable for client environments.

The Client VM also takes advantages of other features of the HotSpot technology such as

• Adaptive Compiler

• Improved Garbage Collection

• Faster Thread Synchronization

Keep in mind that client applications tend to use native libraries to handle hardware intensive operations such as graphics or I/O. The HotSpot technology is not able to help much in this area. In this case, it's really up to the native libraries and hardware performance directly.

Also, client applications tend to do one thing repeatedly such as show a graphics screen and allow the user to press a button. The main features of the HotSpot technology will not be able to help in this area much. Its primary benefits come into play where a "hot" section of code is being executed over and over, which typically happens on a server application. It can help in startup time because not all the code is being compiled as in earlier versions of the virtual machine.

The Java Application Launcher

The Java application launcher is used to launch Java applications and is launched when you type

 java SomeClassFile 

on the command line. By default with the SDK 1.3, the HotSpot Client VM is used. If you need to run the classic virtual machine from 1.2, you can specify a " -classic " option and that virtual machine will be used instead of the HotSpot Client VM. This might be necessary for some development tools that use a different class loader for debugging. You would do something like this to use the classic virtual machine:

 java classic SomeClassFile