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21. Java > Virtual Machines

Virtual Machines

VMs generally improve in performance as time goes on, so you should use the latest version for your platform. Java’s 1.1 event handling is much faster than in 1.02. As an example of an improved VM, here are some of the changes from Sun’s 1.1 to 1.2 Java runtime environments:

  • Each thread keeps its own heap and monitor caches, reducing the overhead of locking and synchronization.

  • Loaded classes are able to take advantage of memory compression and to share String objects among classes.

  • Object allocation speed is greatly improved, as is garbage collection.

  • The 1.2 JDK does not use handles, which are pointers to pointers, but only a single level of indirection to objects. This speeds up object references and allows the elimination of memory fragmentation.


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