What is the importance of jcmd tool in Java 9?

"jcmd" is the JVM Diagnostic tool, which is a command line tool used to target a given JVM locally Run diagnostic commands on the machine. This tool is included in the JDK installation starting from version Java 7 and can be represented by the "%java_home%\bin\jcmd.exe" program file. If we include the "%java_home%\bin" directory in the environment variable "path", we can run the "jcmd -h" command to see the complete list of all directories. Options are as follows

<strong>C:\Users\User>jcmd -h
Usage: jcmd
   or: jcmd -l
   or: jcmd -h

   command must be a valid jcmd command for the selected jvm.
   Use the command "help" to see which commands are available.
   If the pid is 0, commands will be sent to all Java processes.
   The main class argument will be used to match (either partially
   or fully) the class used to start Java.
   If no options are given, lists Java processes (same as -l).

   PerfCounter.print display the counters exposed by this process
   -f read and execute commands from the file
   -l list JVM processes on the local machine
   -h this help</strong>

Example

public class JCmdToolTest {
   public static void main(String args[]) {
      <strong>Runtime </strong>runtime = Runtime.<strong>getRuntime()</strong>;
      System.out.println("Free memory: " + runtime.<strong>freeMemory()</strong>);
      System.out.println("Total memory: " + runtime.<strong>totalMemory()</strong>);
      try {
         Thread.sleep(5000);
      } catch(InterruptedException e) {
      }
   }
}

Output

<strong>Free memory: 65454560
Total memory: 67108864</strong>

##We can use the "

jcmd -l" command line Output all running JVM machines locally and use the PID or class main in the output to identify the JVM.

<strong>C:\Users\User>jcmd -l</strong>
<strong>6108 jdk.jcmd/sun.tools.jcmd.JCmd -l</strong>

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