Use Oracle JDK in Ubuntu

register_oracle_jdk.sh

#!/bin/bash

#user inputs java path
if [[ $1 ]]
then
	JAVA_PATH="$1/bin"

# use JAVA_HOME environment variable
elif [[ $JAVA_HOME ]]
then
	JAVA_PATH="$JAVA_HOME/bin"

else
	echo "I can't even guess where your jdk really is. Please tell me. :("
	exit 1
fi

#JAVA_PATH="/usr/lib/jvm/jdk-15.0.2/bin"

FILES="$(ls $JAVA_PATH)"
for path in $JAVA_PATH/*; do
	file="$(basename $path)"

	# Priority 2000
	# Also enables experimental or decryted features
	sudo update-alternatives --install "/usr/bin/$file" $file $path 2000
done

If you don't know where it was installed likely places candidates are /usr/lib/jvm/ or /opt/java

#!/bin/sh
JAVA_PATH=/usr/lib/jvm/jdk-15.0.2/

sudo update-alternatives --install /usr/bin/java java $JAVA_PATH/bin/java 10 \
    --slave /usr/bin/jaotc jaotc $JAVA_PATH/bin/jaotc\
    --slave /usr/bin/jar jar $JAVA_PATH/bin/jar\
    --slave /usr/bin/jarsigner jarsigner $JAVA_PATH/bin/jarsigner\
    --slave /usr/bin/javac javac $JAVA_PATH/bin/javac\
    --slave /usr/bin/javadoc javadoc $JAVA_PATH/bin/javadoc\
    --slave /usr/bin/javap javap $JAVA_PATH/bin/javap\
    --slave /usr/bin/jcmd jcmd $JAVA_PATH/bin/jcmd\
    --slave /usr/bin/jconsole jconsole $JAVA_PATH/bin/jconsole\
    --slave /usr/bin/jdb jdb $JAVA_PATH/bin/jdb\
    --slave /usr/bin/jdeprscan jdeprscan $JAVA_PATH/bin/jdeprscan\
    --slave /usr/bin/jdeps jdeps $JAVA_PATH/bin/jdeps\
    --slave /usr/bin/jfr jfr $JAVA_PATH/bin/jfr\
    --slave /usr/bin/jhsdb jhsdb $JAVA_PATH/bin/jhsdb\
    --slave /usr/bin/jimage jimage $JAVA_PATH/bin/jimage\
    --slave /usr/bin/jinfo jinfo $JAVA_PATH/bin/jinfo\
    --slave /usr/bin/jlink jlink $JAVA_PATH/bin/jlink\
    --slave /usr/bin/jmap jmap $JAVA_PATH/bin/jmap\
    --slave /usr/bin/jmod jmod $JAVA_PATH/bin/jmod\
    --slave /usr/bin/jpackage jpackage $JAVA_PATH/bin/jpackage\
    --slave /usr/bin/jps jps $JAVA_PATH/bin/jps\
    --slave /usr/bin/jrunscript jrunscript $JAVA_PATH/bin/jrunscript\
    --slave /usr/bin/jshell jshell $JAVA_PATH/bin/jshell\
    --slave /usr/bin/jstack jstack $JAVA_PATH/bin/jstack\
    --slave /usr/bin/jstat jstat $JAVA_PATH/bin/jstat\
    --slave /usr/bin/jstatd jstatd $JAVA_PATH/bin/jstatd\
    --slave /usr/bin/keytool keytool $JAVA_PATH/bin/keytool\
    --slave /usr/bin/rmid rmid $JAVA_PATH/bin/rmid\
    --slave /usr/bin/rmiregistry rmiregistry $JAVA_PATH/bin/rmiregistry\
    --slave /usr/bin/serialver serialver $JAVA_PATH/bin/serialver\
    --slave /usr/share/man/man1/jabswitch.1 jabswitch.1 $JAVA_PATH/man/man1/jabswitch.1\
    --slave /usr/share/man/man1/jaccessinspector.1 jaccessinspector.1 $JAVA_PATH/man/man1/jaccessinspector.1\
    --slave /usr/share/man/man1/jaccesswalker.1 jaccesswalker.1 $JAVA_PATH/man/man1/jaccesswalker.1\
    --slave /usr/share/man/man1/jaotc.1 jaotc.1 $JAVA_PATH/man/man1/jaotc.1\
    --slave /usr/share/man/man1/jar.1 jar.1 $JAVA_PATH/man/man1/jar.1\
    --slave /usr/share/man/man1/jarsigner.1 jarsigner.1 $JAVA_PATH/man/man1/jarsigner.1\
    --slave /usr/share/man/man1/java.1 java.1 $JAVA_PATH/man/man1/java.1\
    --slave /usr/share/man/man1/javac.1 javac.1 $JAVA_PATH/man/man1/javac.1\
    --slave /usr/share/man/man1/javadoc.1 javadoc.1 $JAVA_PATH/man/man1/javadoc.1\
    --slave /usr/share/man/man1/javap.1 javap.1 $JAVA_PATH/man/man1/javap.1\
    --slave /usr/share/man/man1/jcmd.1 jcmd.1 $JAVA_PATH/man/man1/jcmd.1\
    --slave /usr/share/man/man1/jconsole.1 jconsole.1 $JAVA_PATH/man/man1/jconsole.1\
    --slave /usr/share/man/man1/jdb.1 jdb.1 $JAVA_PATH/man/man1/jdb.1\
    --slave /usr/share/man/man1/jdeprscan.1 jdeprscan.1 $JAVA_PATH/man/man1/jdeprscan.1\
    --slave /usr/share/man/man1/jdeps.1 jdeps.1 $JAVA_PATH/man/man1/jdeps.1\
    --slave /usr/share/man/man1/jfr.1 jfr.1 $JAVA_PATH/man/man1/jfr.1\
    --slave /usr/share/man/man1/jhsdb.1 jhsdb.1 $JAVA_PATH/man/man1/jhsdb.1\
    --slave /usr/share/man/man1/jinfo.1 jinfo.1 $JAVA_PATH/man/man1/jinfo.1\
    --slave /usr/share/man/man1/jlink.1 jlink.1 $JAVA_PATH/man/man1/jlink.1\
    --slave /usr/share/man/man1/jmap.1 jmap.1 $JAVA_PATH/man/man1/jmap.1\
    --slave /usr/share/man/man1/jmod.1 jmod.1 $JAVA_PATH/man/man1/jmod.1\
    --slave /usr/share/man/man1/jpackage.1 jpackage.1 $JAVA_PATH/man/man1/jpackage.1\
    --slave /usr/share/man/man1/jps.1 jps.1 $JAVA_PATH/man/man1/jps.1\
    --slave /usr/share/man/man1/jrunscript.1 jrunscript.1 $JAVA_PATH/man/man1/jrunscript.1\
    --slave /usr/share/man/man1/jshell.1 jshell.1 $JAVA_PATH/man/man1/jshell.1\
    --slave /usr/share/man/man1/jstack.1 jstack.1 $JAVA_PATH/man/man1/jstack.1\
    --slave /usr/share/man/man1/jstat.1 jstat.1 $JAVA_PATH/man/man1/jstat.1\
    --slave /usr/share/man/man1/jstatd.1 jstatd.1 $JAVA_PATH/man/man1/jstatd.1\
    --slave /usr/share/man/man1/keytool.1 keytool.1 $JAVA_PATH/man/man1/keytool.1\
    --slave /usr/share/man/man1/kinit.1 kinit.1 $JAVA_PATH/man/man1/kinit.1\
    --slave /usr/share/man/man1/klist.1 klist.1 $JAVA_PATH/man/man1/klist.1\
    --slave /usr/share/man/man1/ktab.1 ktab.1 $JAVA_PATH/man/man1/ktab.1\
    --slave /usr/share/man/man1/rmid.1 rmid.1 $JAVA_PATH/man/man1/rmid.1\
    --slave /usr/share/man/man1/rmiregistry.1 rmiregistry.1 $JAVA_PATH/man/man1/rmiregistry.1\
    --slave /usr/share/man/man1/serialver.1 serialver.1 $JAVA_PATH/man/man1/serialver.1