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Using -XX command-line options

Java™ VM command-line options that are specified with -XX: are not checked for validity. If the VM does not recognize the option, the option is ignored. These options can therefore be used across different VM versions without ensuring a particular level of the VM. If you want to turn off this behavior to test whether your -XX options are valid, use the -XX:-IgnoreUnrecognizedXXColonOptions option.

For options that take a <size> parameter, add a suffix to the size value: "k" or "K" to indicate kilobytes, "m" or "M" to indicate megabytes, "g" or "G" to indicate gigabytes, or "t" or "T" to indicate terabytes.

For example, to set the -XX:MaxDirectMemorySize value to 16 MB, you can specify -XX:MaxDirectMemorySize16M, -XX:MaxDirectMemorySize16m, -XX:MaxDirectMemorySize16384K, or XX:MaxDirectMemorySize16384k on the command line.