What is 64 bit Java ?

A 64-bit version of Java has been available to Solaris SPARC users since the 1.4.0 release of J2SE. A 64-bit capable J2SE is an implementation of the Java SDK (and the JRE along with it) that runs in the 64-bit environment of a 64-bit OS on a 64-bit processor. The primary advantage of running Java in a 64-bit environment is the larger address space.

This allows for a much larger Java heap size and an increased maximum number of Java Threads, which is needed for certain kinds of large or long-running applications. The primary complication in doing such a port is that the sizes of some native data types are changed. Not surprisingly the size of pointers is increased to 64 bits. On Solaris and most Unix platforms, the size of the C language long is also increased to 64 bits. Any native code in the 32-bit SDK implementation that relied on the old sizes of these data types is likely to require updating.

Within the parts of the SDK written in Java things are simpler, since Java specifies the sizes of its primitive data types precisely. However even some Java code needs updating, such as when a Java int is used to store a value passed to it from a part of the implementation written in C.