CODEWITHSUNDEEP
jvm
DeepNightTwo
DeepNightTwo

Reputation: 4951

What is the difference between -, -X params and -XX params in JVM?

There are lots of parameters for JVM. Some start with -, such as -server, -client. Some start with -X, such as -Xms, -Xmx. Some start with -XX, such as -XX:PermSize, -XX:UseParallelGC.

Since these parameters are not duplicated, why start with so many different prefix? Why not just use -. My guess is there are some kind of standards for this. The -XX parameters are extension settings and not supported by all JVM impls. Is that so?

Upvotes: 22

Views: 8011

Answers (4)

Premraj
Premraj

Reputation: 74571

These are three main categories of Command-Line Argument options:

  • Standard options :Options that begin with - are Standard options are expected to be accepted by all JVM implementations and are stable between releases (though they can be deprecated).

  • Non-standard options :Options that begin with -X are non-standard (not guaranteed to be supported on all JVM implementations), and are subject to change without notice in subsequent releases of the Java SDK.

  • Developer options :Options that begin with -XX are developer options and often have specific system requirements for correct operation and may require privileged access to system configuration parameters; they are not recommended for casual use. These options are also subject to change without notice.

src

Upvotes: 13

rai.skumar
rai.skumar

Reputation: 10667

  • 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.

Java Reference

Upvotes: 2

P.T.
P.T.

Reputation: 25177

Yeah, its the level of support. The vanilla ("-") options are supported in future versions, and the X are not supported. Further, the XX options are "not recommended for casual use".

For an example, see IBM's JVM documentation: http://publib.boulder.ibm.com/infocenter/javasdk/v6r0/index.jsp?topic=%2Fcom.ibm.java.doc.user.aix64.60%2Fdiag%2Fappendixes%2Fcmdline%2Fcommands_jvm.html

Upvotes: 7

Prince John Wesley
Prince John Wesley

Reputation: 63688

java -help:

-X     Displays information about non-standard options and exit

Upvotes: 1

Related Questions