src/Pure/Tools/java_monitor.scala

--- a/src/Pure/Tools/java_monitor.scala	Mon Dec 21 23:22:14 2020 +0100
+++ b/src/Pure/Tools/java_monitor.scala	Tue Dec 22 15:49:22 2020 +0100
@@ -9,7 +9,8 @@
 
 import java.awt.Component
 import javax.swing.UIManager
-import sun.tools.jconsole.{JConsole, LocalVirtualMachine, VMPanel, ProxyClient}
+import sun.tools.jconsole.{JConsole, LocalVirtualMachine, VMPanel, ProxyClient,
+  Messages, Resources => JConsoleResources}
 
 
 object Java_Monitor
@@ -40,6 +41,13 @@
           System.setProperty("swing.defaultlaf", laf)
       }
 
+      Desktop_App.about_handler {
+        GUI.dialog(null, "Java Monitor",
+          JConsoleResources.format(
+            Messages.JCONSOLE_VERSION, System.getProperty("java.runtime.version"))
+        )
+      }
+
       val jconsole = new JConsole(false)
 
       val screen = GUI.mouse_location()