What is the importance of jdeps tool in Java 9?

The jdeps is a Java Class Dependency Analyzer tool, which is a command-line tool to show the package-level or class-level dependencies of given Java class files. The input classes can be given as a path-name to a .class file, a directory, a jar file, or it will be a fully qualified class name to analyze all class files.

"jdeps" has included in the jdk installation since jdk 8 and, it is represented by the "%java_home%\bin\jdeps.exe" program file. If we have "%java_home%\bin" directory included in the "path" environment variable, we will run "jdeps --help" command to see a complete list of all options. 

Below, we can able see a list of options by using the "jdeps --help" command.

C:\Program Files\Java\jdk-9.0.4>jdeps --help
Usage: jdeps <options> <path ...>]
<path> can be a pathname to a .class file, a directory, a JAR file.

Possible options include:
  -dotoutput <dir>
  --dot-output <dir>      Destination directory for DOT file output
  -s        -summary      Print dependency summary only.
  -v        -verbose      Print all class level dependences
                          Equivalent to -verbose:class -filter:none.
  -verbose:package        Print package-level dependences excluding
                          dependences within the same package by default
  -verbose:class          Print class-level dependences excluding
                          dependences within the same package by default
  --api-only              Restrict analysis to APIs i.e. dependences
                          from the signature of public and protected
                          members of public classes including field
                          type, method parameter types, returned type,
                          checked exception types etc.
  --jdk-internals         Finds class-level dependences on JDK internal
                          APIs. By default, it analyzes all classes
                          on --class-path and input files unless -include
                          option is specified. This option cannot be
                          used with -p, -e and -s options.
                          WARNING: JDK internal APIs are inaccessible.
--check <module-name>[,<module-name>...
                          Analyze the dependence of the specified modules
                          It prints the module descriptor, the resulting
                          module dependences after analysis and the
                          graph after transition reduction. It also
                          identifies any unused qualified exports.
  --generate-module-info <dir>
                          Generate module-info.java under the specified
                          directory. The specified JAR files will be
                          analyzed. This option cannot be used with
                          --dot-output or --class-path. Use
                          --generate-open-module option for open modules.
  --generate-open-module <dir>
                          Generate module-info.java for the specified
                          JAR files under the specified directory as
                          open modules. This option cannot be used with
                          --dot-output or --class-path.
  --list-deps             Lists the dependences and use of JDK internal APIs.
  --list-reduced-deps     Same as --list-deps with not listing
                          the implied reads edges from the module graph
                          If module M1 depends on M2 and M3,
                          M2 requires public on M3, then M1 reading M3 is
                          implied and removed from the module graph.
  -cp <path>
  -classpath <path>
  --class-path <path>     Specify where to find class files
  --module-path <module path>
                          Specify module path
  --upgrade-module-path <module path>
                          Specify upgrade module path
  --system <java-home>    Specify an alternate system module path
  --add-modules <module-name>[,<module-name>...]
                          Adds modules to the root set for analysis
  -m <module-name>
  --module <module-name>  Specify the root module for analysis
  --multi-release <version>
                          Specifies the version when processing
                          multi-release jar files. should
                          be integer >= 9 or base.

Options to filter dependences:
  -p <pkg>
  -package <pkg>
  --package <pkg>           Finds dependences matching the given package
                            name (may be given multiple times).
  -e <regex>
  -regex <regex>
  --regex <regex>           Finds dependences matching the given pattern.
  --require <module-name>   Finds dependences matching the given module
                            name (may be given multiple times). --package,
                            --regex, --require are mutual exclusive.
  -f <regex> -filter <regex> Filter dependences matching the given
                             pattern. If given multiple times, the last
                             one will be used.
  -filter:package            Filter dependences within the same package.
                             This is the default.
  -filter:archive            Filter dependences within the same archive.
  -filter:module             Filter dependences within the same module.
  -filter:none               No -filter:package and -filter:archive
                             filtering. Filtering specified via the
                             -filter option still applies.

Options to filter classes to be analyzed:
  -include <regex>           Restrict analysis to classes matching pattern
                             This option filters the list of classes to
                             be analyzed. It can be used together with
                             -p and -e which apply pattern to the dependences

  -P         -profile        Show profile containing a package
  -R         -recursive      Recursively traverse all run-time dependences.
                             The -R option implies -filter:none. If -p,
                             -e, -f option is specified, only the matching
                             dependences are analyzed.
  -I          --inverse      Analyzes the dependences per other given options

                             and then find all artifacts that directly
                             and indirectly depend on the matching nodes.
                             This is equivalent to the inverse of
                             compile-time view analysis and print
                             dependency summary. This option must use
                             with --require, --package or --regex option.
  --compile-time             Compile-time view of transitive dependences
                             i.e. compile-time view of -R option.
                             Analyzes the dependences per other given options
                             If a dependence is found from a directory,
                             a JAR file or a module, all c*lasses in that
                             containing archive are analyzed.
  -q           - quiet       Do not show missing dependences from
                             --generate-module-info output.
  -version     --version     Version information