If, like me you’ve recently moved Java 8 to 11, you might noticed Java VisualVM has gone. It now needs installing separately and annoying still needs Java 8 to run. So on a system with only J11, you’ll need to:
sudo apt-get -y install visualvm
sudo apt-get install openjdk-8-jdk
visualvm --jdkhome "/usr/lib/jvm/java-1.8.0-openjdk-amd64"
Ewen's Technical Blog 