If you installed JDP here: /usr/local/java/jdk-9.0.4
update-alternatives --remove-all "javac"
update-alternatives --remove-all "javaws"
update-alternatives --remove-all "rmid"
update-alternatives --remove-all "java"
update-alternatives --remove-all "keytool"
update-alternatives --remove-all "jhsdb"
update-alternatives --remove-all "jjs"
update-alternatives --remove-all "pack200"
update-alternatives --remove-all "rmiregistry"
update-alternatives --remove-all "unpack200"
update-alternatives --remove-all "orbd"
update-alternatives --remove-all "servertool"
update-alternatives --remove-all "tnameserv"
update-alternatives --remove-all "jexec"
update-alternatives --remove-all "jarsigner"
update-alternatives --remove-all "javadoc"
update-alternatives --remove-all "javah"
update-alternatives --remove-all "javap"
update-alternatives --remove-all "javapackager"
update-alternatives --remove-all "jcmd"
update-alternatives --remove-all "jconsole"
update-alternatives --remove-all "jcontrol"
update-alternatives --remove-all "jdb"
update-alternatives --remove-all "jdeps"
update-alternatives --remove-all "jinfo"
update-alternatives --remove-all "jmap"
update-alternatives --remove-all "jmc"
update-alternatives --remove-all "jps"
update-alternatives --remove-all "jrunscript"
update-alternatives --remove-all "jstack"
update-alternatives --remove-all "jstat"
update-alternatives --remove-all "jstatd"
update-alternatives --remove-all "jvisualvm"
update-alternatives --remove-all "jaotc"
update-alternatives --remove-all "jar"
update-alternatives --remove-all "jdeprscan"
update-alternatives --remove-all "jimage"
update-alternatives --remove-all "jlink"
update-alternatives --remove-all "jmod"
update-alternatives --remove-all "jshell"
update-alternatives --remove-all "jweblauncher"update-alternatives --install "/usr/bin/javac" javac "/usr/local/java/jdk-9.0.4/bin/javac" 1
update-alternatives --install "/usr/bin/javaws" javaws "/usr/local/java/jdk-9.0.4/bin/javaws" 1
update-alternatives --install "/usr/bin/rmid" rmid "/usr/local/java/jdk-9.0.4/bin/rmid" 1
update-alternatives --install "/usr/bin/java" java "/usr/local/java/jdk-9.0.4/bin/java" 1
update-alternatives --install "/usr/bin/keytool" keytool "/usr/local/java/jdk-9.0.4/bin/keytool" 1
update-alternatives --install "/usr/bin/jhsdb" jhsdb "/usr/local/java/jdk-9.0.4/bin/jhsdb" 1
update-alternatives --install "/usr/bin/jjs" jjs "/usr/local/java/jdk-9.0.4/bin/jjs" 1
update-alternatives --install "/usr/bin/pack200" pack200 "/usr/local/java/jdk-9.0.4/bin/pack200" 1
update-alternatives --install "/usr/bin/rmiregistry" rmiregistry "/usr/local/java/jdk-9.0.4/bin/rmiregistry" 1
update-alternatives --install "/usr/bin/unpack200" unpack200 "/usr/local/java/jdk-9.0.4/bin/unpack200" 1
update-alternatives --install "/usr/bin/orbd" orbd "/usr/local/java/jdk-9.0.4/bin/orbd" 1
update-alternatives --install "/usr/bin/servertool" servertool "/usr/local/java/jdk-9.0.4/bin/servertool" 1
update-alternatives --install "/usr/bin/tnameserv" tnameserv "/usr/local/java/jdk-9.0.4/bin/tnameserv" 1
update-alternatives --install "/usr/bin/jexec" jexec "/usr/local/java/jdk-9.0.4/lib/jexec" 1
update-alternatives --install "/usr/bin/jarsigner" jarsigner "/usr/local/java/jdk-9.0.4/bin/jarsigner" 1
update-alternatives --install "/usr/bin/javadoc" javadoc "/usr/local/java/jdk-9.0.4/bin/javadoc" 1
update-alternatives --install "/usr/bin/javah" javah "/usr/local/java/jdk-9.0.4/bin/javah" 1
update-alternatives --install "/usr/bin/javap" javap "/usr/local/java/jdk-9.0.4/bin/javap" 1
update-alternatives --install "/usr/bin/javapackager" javapackager "/usr/local/java/jdk-9.0.4/bin/javapackager" 1
update-alternatives --install "/usr/bin/jcmd" jcmd "/usr/local/java/jdk-9.0.4/bin/jcmd" 1
update-alternatives --install "/usr/bin/jconsole" jconsole "/usr/local/java/jdk-9.0.4/bin/jconsole" 1
update-alternatives --install "/usr/bin/jcontrol" jcontrol "/usr/local/java/jdk-9.0.4/bin/jcontrol" 1
update-alternatives --install "/usr/bin/jdb" jdb "/usr/local/java/jdk-9.0.4/bin/jdb" 1
update-alternatives --install "/usr/bin/jdeps" jdeps "/usr/local/java/jdk-9.0.4/bin/jdeps" 1
update-alternatives --install "/usr/bin/jinfo" jinfo "/usr/local/java/jdk-9.0.4/bin/jinfo" 1
update-alternatives --install "/usr/bin/jmap" jmap "/usr/local/java/jdk-9.0.4/bin/jmap" 1
update-alternatives --install "/usr/bin/jmc" jmc "/usr/local/java/jdk-9.0.4/bin/jmc" 1
update-alternatives --install "/usr/bin/jps" jps "/usr/local/java/jdk-9.0.4/bin/jps" 1
update-alternatives --install "/usr/bin/jrunscript" jrunscript "/usr/local/java/jdk-9.0.4/bin/jrunscript" 1
update-alternatives --install "/usr/bin/jstack" jstack "/usr/local/java/jdk-9.0.4/bin/jstack" 1
update-alternatives --install "/usr/bin/jstat" jstat "/usr/local/java/jdk-9.0.4/bin/jstat" 1
update-alternatives --install "/usr/bin/jstatd" jstatd "/usr/local/java/jdk-9.0.4/bin/jstatd" 1
update-alternatives --install "/usr/bin/jvisualvm" jvisualvm "/usr/local/java/jdk-9.0.4/bin/jvisualvm" 1
update-alternatives --install "/usr/bin/jaotc" jaotc "/usr/local/java/jdk-9.0.4/bin/jaotc" 1
update-alternatives --install "/usr/bin/jar" jar "/usr/local/java/jdk-9.0.4/bin/jar" 1
update-alternatives --install "/usr/bin/jdeprscan" jdeprscan "/usr/local/java/jdk-9.0.4/bin/jdeprscan" 1
update-alternatives --install "/usr/bin/jimage" jimage "/usr/local/java/jdk-9.0.4/bin/jimage" 1
update-alternatives --install "/usr/bin/jlink" jlink "/usr/local/java/jdk-9.0.4/bin/jlink" 1
update-alternatives --install "/usr/bin/jmod" jmod "/usr/local/java/jdk-9.0.4/bin/jmod" 1
update-alternatives --install "/usr/bin/jshell" jshell "/usr/local/java/jdk-9.0.4/bin/jshell" 1
update-alternatives --install "/usr/bin/jweblauncher" jweblauncher "/usr/local/java/jdk-9.0.4/bin/jweblauncher" 1