[转]怎样用Java运行64位程序

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32位下JVM最大可用内存<4g
$ java -showversion -Xmx4g HelloWorld
Invalid maximum heap size: -Xmx6g
The specified size exceeds the maximum representable size.
Could not create the Java virtual machine.
所需内存超过4g，需开启64位标记
$ java -showversion -d64 -Xmx6g HelloWorld
java version "1.6.0_07"
Java(TM) SE Runtime Environment (build 1.6.0_07-b04)
Java HotSpot(TM) 64-Bit Server VM (build 10.0-b23, mixed mode)
Hello world!
系统平台不支持64位时会提示：
Running a 64-bit JVM is not supported on this platform.
物理内存不够时会提示：
Error occorred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.
p.s. 开启64位标记在Linux下使用-d，win32下使用-D。(linux jdk1.5,1.6; win32 jdk1.6经过我的测试)