JDK 6 Virtual Machine (VM)-related APIs & Developer

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The JDKTM provides one or more implementations of the JavaTMvirtual machine (VM):

• On platforms typically used for client applications, the JDK comes with a VM implementation called the Java HotSpotTM Client VM(client VM). The client VM is tuned for reducing start-up time and memory footprint. It can be invoked by using the-client command-line option when launching an application.
• On all platforms, the JDK comes with an implementation of the Java virtual machine called the Java HotSpot Server VM(server VM). The server VM is designed for maximum program execution speed. It can be invoked by using the-server command-line option when launching an application.

Some features of Java HotSpot technology, common to both VM implementations, are the following.

• Adaptive compiler - Applications are launched using a standard interpreter, but the code is then analyzed as it runs to detect performance bottlenecks, or "hot spots". The Java HotSpot VMs compile those performance-critical portions of the code for a boost in performance, while avoiding unnecessary compilation of seldom-used code (most of the program). The Java HotSpot VMs also use the adaptive compiler to decide, on the fly, how best to optimize compiled code with techniques such as in-lining. The runtime analysis performed by the compiler allows it to eliminate guesswork in determining which optimizations will yield the largest performance benefit.
• Rapid memory allocation and garbage collection - Java HotSpot technology provides for rapid memory allocation for objects, and it offers a choice of fast, efficient, state-of-the-art garbage collectors.
• Thread synchronization - The Java programming language allows for use of multiple, concurrent paths of program execution (called "threads"). Java HotSpot technology provides a thread-handling capability that is designed to scale readily for use in large, shared-memory multiprocessor servers.