I also did a fresh install of elastic search and got the issue below:
simon@simon:~/Downloads$ sudo dpkg -i elasticsearch-6.7.1.deb
[sudo] password for simon:
Selecting previously unselected package elasticsearch.
(Reading database ... 175469 files and directories currently installed.)
Preparing to unpack elasticsearch-6.7.1.deb ...
/usr/bin/java
Creating elasticsearch group... OK
Creating elasticsearch user... OK
Unpacking elasticsearch (6.7.1) ...
Setting up elasticsearch (6.7.1) ...
warning: Falling back to java on path. This behavior is deprecated. Specify JAVA_HOME
Created elasticsearch keystore in /etc/elasticsearch
Processing triggers for systemd (237-3ubuntu10.15) ...
Processing triggers for ureadahead (0.100.0-20) ...
simon@simon:~/Downloads$ echo $JAVA_HOME
/usr/lib/jvm/java-11-openjdk-amd64/bin/