~$ java
Usage: java [options] <mainclass> [args...]
           (to execute a class)
   or  java [options] -jar <jarfile> [args...]
           (to execute a jar file)
   or  java [options] -m <module>[/<mainclass>] [args...]
       java [options] --module <module>[/<mainclass>] [args...]
           (to execute the main class in a module)
   or  java [options] <sourcefile> [args]
           (to execute a single source-file program)
 Arguments following the main class, source file, -jar <jarfile>,
 -m or --module <module>/<mainclass> are passed as the arguments to
 main class.
 where options include:
    -zero         to select the "zero" VM
    -dcevm        to select the "dcevm" VM
    -cp <class search path of directories and zip/jar files>
    -classpath <class search path of directories and zip/jar files>
    --class-path <class search path of directories and zip/jar files>
                  A : separated list of directories, JAR archives,
                  and ZIP archives to search for class files.
    -p <module path>
    --module-path <module path>...
                  A : separated list of directories, each directory
                  is a directory of modules.
    --upgrade-module-path <module path>...
                  A : separated list of directories, each directory
                  is a directory of modules that replace upgradeable
                  modules in the runtime image
    --add-modules <module name>[,<module name>...]
                  root modules to resolve in addition to the initial module.
                  <module name> can also be ALL-DEFAULT, ALL-SYSTEM,
                  ALL-MODULE-PATH.
    --enable-native-access <module name>[,<module name>...]
                  modules that are permitted to perform restricted native operations.
                  <module name> can also be ALL-UNNAMED.
    --list-modules
                  list observable modules and exit
    -d <module name>
    --describe-module <module name>
                  describe a module and exit
    --dry-run     create VM and load main class but do not execute main method.
                  The --dry-run option may be useful for validating the
                  command-line options such as the module system configuration.
    --validate-modules
                  validate all modules and exit
                  The --validate-modules option may be useful for finding
                  conflicts and other errors with modules on the module path.
    -D<name>=<value>
                  set a system property
    -verbose:[class|module|gc|jni]
                  enable verbose output for the given subsystem
    -version      print product version to the error stream and exit
    --version     print product version to the output stream and exit
    -showversion  print product version to the error stream and continue
    --show-version
                  print product version to the output stream and continue
    --show-module-resolution
                  show module resolution output during startup
    -? -h -help
                  print this help message to the error stream
    --help        print this help message to the output stream
    -X            print help on extra options to the error stream
    --help-extra  print help on extra options to the output stream
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:jdwp
                  see also -agentlib:jdwp=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
                  HiDPI scaled images are automatically supported and used
                  if available. The unscaled image filename, e.g. image.ext,
                  should always be passed as the argument to the -splash option.
                  The most appropriate scaled image provided will be picked up
                  automatically.
                  See the SplashScreen API documentation for more information
    @argument files
                  one or more argument files containing options
    -disable-@files
                  prevent further argument file expansion
    --enable-preview
                  allow classes to depend on preview features of this release
To specify an argument for a long option, you can use --<name>=<value> or
--<name> <value>.

System.getProperty("user"); //Alice 

System.setProperty("user", "Bob"); 

$ java -X
    -Xbatch           disable background compilation
    -Xbootclasspath/a:<directories and zip/jar files separated by :>
                      append to end of bootstrap class path
    -Xcheck:jni       perform additional checks for JNI functions
    -Xcomp            forces compilation of methods on first invocation
    -Xdebug           does nothing. Provided for backward compatibility.
    -Xdiag            show additional diagnostic messages
    -Xfuture          enable strictest checks, anticipating future default.
                      This option is deprecated and may be removed in a
                      future release.
    -Xint             interpreted mode execution only
    -Xinternalversion
                      displays more detailed JVM version information than the
                      -version option
    -Xlog:<opts>      Configure or enable logging with the Java Virtual
                      Machine (JVM) unified logging framework. Use -Xlog:help
                      for details.
    -Xloggc:<file>    log GC status to a file with time stamps.
                      This option is deprecated and may be removed in a
                      future release. It is replaced by -Xlog:gc:<file>.
    -Xmixed           mixed mode execution (default)
    -Xmn<size>        sets the initial and maximum size (in bytes) of the heap
                      for the young generation (nursery)
    -Xms<size>        set initial Java heap size
    -Xmx<size>        set maximum Java heap size
    -Xnoclassgc       disable class garbage collection
    -Xrs              reduce use of OS signals by Java/VM (see documentation)
    -Xshare:auto      use shared class data if possible (default)
    -Xshare:off       do not attempt to use shared class data
    -Xshare:on        require using shared class data, otherwise fail.
                      This is a testing option and may lead to intermittent
                      failures. It should not be used in production environments.
    -XshowSettings    show all settings and continue
    -XshowSettings:all
                      show all settings and continue
    -XshowSettings:locale
                      show all locale related settings and continue
    -XshowSettings:properties
                      show all property settings and continue
    -XshowSettings:vm
                      show all vm related settings and continue
    -XshowSettings:system
                      (Linux Only) show host system or container
                      configuration and continue
    -Xss<size>        set java thread stack size
    -Xverify          sets the mode of the bytecode verifier
                      Note that option -Xverify:none is deprecated and
                      may be removed in a future release.
    --add-reads <module>=<target-module>(,<target-module>)*
                      updates <module> to read <target-module>, regardless
                      of module declaration.
                      <target-module> can be ALL-UNNAMED to read all unnamed
                      modules.
    --add-exports <module>/<package>=<target-module>(,<target-module>)*
                      updates <module> to export <package> to <target-module>,
                      regardless of module declaration.
                      <target-module> can be ALL-UNNAMED to export to all
                      unnamed modules.
    --add-opens <module>/<package>=<target-module>(,<target-module>)*
                      updates <module> to open <package> to
                      <target-module>, regardless of module declaration.
    --limit-modules <module name>[,<module name>...]
                      limit the universe of observable modules
    --patch-module <module>=<file>(:<file>)*
                      override or augment a module with classes and resources
                      in JAR files or directories.
    --source <version>
                      set the version of the source in source-file mode.
These extra options are subject to change without notice.

$ java -XX:+PrintFlagsFinal -version
[Global flags]
// ...
size_t AsyncLogBufferSize                       = 2097152                                   {product} {default}
  intx AutoBoxCacheMax                          = 128                                    {C2 product} {default}
  intx BCEATraceLevel                           = 0                                         {product} {default}
  bool BackgroundCompilation                    = true                                   {pd product} {default}
size_t BaseFootPrintEstimate                    = 268435456                                 {product} {default}
  intx BiasedLockingBulkRebiasThreshold         = 20                                        {product} {default}
  intx BiasedLockingBulkRevokeThreshold         = 40                                        {product} {default}
  intx BiasedLockingDecayTime                   = 25000                                     {product} {default}
  intx BiasedLockingStartupDelay                = 0                                         {product} {default}
// ... 
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu120.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu120.04, mixed mode, sharing)

$ java -XX:+PrintFlagsFinal -version | grep command
     bool PrintFlagsFinal                          = true                                      {product} {command line}

$ java -XX:+PrintFlagsWithComments -version
Error: VM option 'PrintFlagsWithComments' is notproduct and is available only in debug version of VM.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

$ java -XX:+PrintFlagsInitial -version | wc -l
559
$ java -XX:+PrintFlagsFinal -version | wc -l
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu120.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu120.04, mixed mode, sharing)
559

$ diff <(java -XX:+PrintFlagsInitial -version) <(java -XX:+PrintFlagsFinal -version)

$ java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | wc -l
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu120.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu120.04, mixed mode, sharing)
771

$ java -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+PrintFlagsFinal -version | w
c -l
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu120.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu120.04, mixed mode, sharing)
891

$ java -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+JVMCIPrintProperties -XX:+EnableJVMCI -XX:+PrintFlagsFinal -version | wc -l 908 

java -XX:+PrintCommandLineFlags -version
-XX:ConcGCThreads=2 -XX:G1ConcRefinementThreads=8 -XX:GCDrainStackTargetSize=64 -XX:InitialHeapSize=62422080 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=998753280 -XX:MinHeapSize=6815736 -XX:+PrintCommandLineFlags -XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu120.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu120.04, mixed mode, sharing)