JVM 参数 -X 与 -XX

JVM 参数 -X -XX 参数，两者都不是稳定的，-X 要区分版本

• Options that begin with -X are non-standard (not guaranteed to be supported on all VM implementations), and are subject to change without notice in subsequent releases of the JDK.
• Options that are specified with -XX are not stable and are subject to change without notice.

• -X 可以通过 java -X 查看当前版本支持的所有参数
• -XX 可以通过 java -XX:+PrintFlagsFinal 打印所有系统参数的值
  • -XX:+PrintVMOptions 程序运行时，打印虚拟机接收的命令行显式参数。
  • -XX:+PrintCommandLineFlags 打印传递给虚拟机的显式和隐式参数。

-XX 有两种类型，boolean 类型和非boolean类型(number or string)

• boolean 类型，-XX:[±]参数
• 非boolean类型，-XX:参数=？

• Boolean options are turned on with -XX:+<option> and turned off with -XX:-<option>.Disa
• Numeric options are set with -XX:<option>=<number>. Numbers can include ‘m’ or ‘M’ for megabytes, ‘k’ or ‘K’ for kilobytes, and ‘g’ or ‘G’ for gigabytes (for example, 32k is the same as 32768).
• String options are set with -XX:<option>=<string>, are usually used to specify a file, a path, or a list of commands

• https://www.oracle.com/java/technologies/javase/vmoptions-jsp.html