Java命令行如何查看帮助

在Java命令行中，你可以使用java -help或java --help命令来查看帮助信息。这将显示Java运行时环境的基本用法和选项。以下是一个示例输出：

Usage: java [options] <mainclass> [args...]
           (to execute a class)
   or  java [options] -jar jarfile [args...]
           (to execute a jar file)
where options include:
    -client       to use the client VM
    -server       to use the server VM
    -hotspot      to use the hotspot VM
    -fastdebug    to start the JVM in fast debug mode
    -slowdebug    to start the JVM in slow debug mode
    -genassert    generate assertions
    -X            enable non-standard options
    -XX:Option     set option using the syntax "-XX:option=value"

Options that take arguments:
    -Dproperty=value
                 set a system property
    -Xbootclasspath:<pathlist>
                 specify boot class path entries
    -classpath <pathlist>
                 specify class path
    -Djava.library.path=<pathlist>
                 specify native library path
    -verbose[:class|gc|jni]
                 enable verbose output
    -version      print product version
    -showversion  print product version and copyright
    -jre-restrict-search | -no-jre-restrict-search
                 restrict the JRE search to the jre directory

The following environment variables are examined when searching for the java executable:
    JAVA_HOME               set the Java home value
    JRE_HOME                set the JRE home value
    CLASSPATH               specified class path
    PATH                    specifies a list of directories to search for classes

See http://java.sun.com/docs/hotspot/ for information about the
Java HotSpot(TM) Virtual Machine.

Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

这个输出包含了Java命令行的基本用法、选项和参数。请注意，这个输出可能会因Java版本而异。