Starting with JDK 12, the location of the jconsole Online User Guide has moved. It used to be located at:

https://docs.oracle.com/javase/<version>/docs/technotes/guides/management/jconsole.html

Starting with JDK 12 it is located at:

https://docs.oracle.com/en/java/javase/<version>/docs/specs/man/jconsole.html

The jconsole Help -> "Online User Guide" menu item is suppose to take you to this URL, but currently points to the old style location, which doesn't work. The following update is needed:

diff --git a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages.properties b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages.properties
index 24c2209ad0d..8af36f5d148 100644
--- a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages.properties
+++ b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages.properties
@@ -129,7 +129,7 @@ HELP_ABOUT_DIALOG_JAVA_VERSION=Java VM version:<br>{0}
 HELP_ABOUT_DIALOG_MASTHEAD_ACCESSIBLE_NAME=Masthead Graphic
 HELP_ABOUT_DIALOG_MASTHEAD_TITLE=About JConsole
 HELP_ABOUT_DIALOG_TITLE=JConsole: About
-HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=http://docs.oracle.com/javase/{0}/docs/technotes/guides/management/jconsole.html
+HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=https://docs.oracle.com/en/java/javase/{0}/docs/specs/man/jconsole.html
 HELP_MENU_ABOUT_TITLE=&About JConsole
 HELP_MENU_USER_GUIDE_TITLE=Online &User Guide
 HELP_MENU_TITLE=&Help
diff --git a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_ja.properties b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_ja.properties
index 2847da2e0a2..1ec346a36a5 100644
--- a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_ja.properties
+++ b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_ja.properties
@@ -130,6 +130,7 @@ HELP_ABOUT_DIALOG_MASTHEAD_ACCESSIBLE_NAME=\u30DE\u30B9\u30C8\u30D8\u30C3\u30C9\
 HELP_ABOUT_DIALOG_MASTHEAD_TITLE=JConsole\u306B\u3064\u3044\u3066
 HELP_ABOUT_DIALOG_TITLE=JConsole: \u8A73\u7D30
 HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=http://docs.oracle.com/javase/{0}/docs/technotes/guides/management/jconsole.html
+HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=https://docs.oracle.com/en/java/javase/{0}/docs/specs/man/jconsole.html
 HELP_MENU_ABOUT_TITLE=JConsole\u306B\u3064\u3044\u3066(&A)
 HELP_MENU_USER_GUIDE_TITLE=\u30AA\u30F3\u30E9\u30A4\u30F3\u30FB\u30E6\u30FC\u30B6\u30FC\u30FB\u30AC\u30A4\u30C9(&U)
 HELP_MENU_TITLE=\u30D8\u30EB\u30D7(&H)
diff --git a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_zh_CN.properties b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_zh_CN.properties
index 1541bf99968..57943d5f007 100644
--- a/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_zh_CN.properties
+++ b/src/jdk.jconsole/share/classes/sun/tools/jconsole/resources/messages_zh_CN.properties
@@ -129,7 +129,7 @@ HELP_ABOUT_DIALOG_JAVA_VERSION=Java VM \u7248\u672C:<br>{0}
 HELP_ABOUT_DIALOG_MASTHEAD_ACCESSIBLE_NAME=\u62A5\u5934\u56FE
 HELP_ABOUT_DIALOG_MASTHEAD_TITLE=\u5173\u4E8E JConsole
 HELP_ABOUT_DIALOG_TITLE=JConsole: \u5173\u4E8E
-HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=http://docs.oracle.com/javase/{0}/docs/technotes/guides/management/jconsole.html
+HELP_ABOUT_DIALOG_USER_GUIDE_LINK_URL=https://docs.oracle.com/en/java/javase/{0}/docs/specs/man/jconsole.html
 HELP_MENU_ABOUT_TITLE=\u5173\u4E8E JConsole(&A)
 HELP_MENU_USER_GUIDE_TITLE=\u8054\u673A\u7528\u6237\u6307\u5357(&U)
 HELP_MENU_TITLE=\u5E2E\u52A9(&H)