java -version does not work

Question

I install Oracle java 1.8.0_101 manually on Debian 10 for hadoop uses, I have found this tutorial : https://www.digitalocean.com/community/tutorials/how-to-manually-install-oracle-java-on-a-debian-or-ubuntu-vps . I execute this after extracting the .tar file in /etc/jdk:

update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_101/bin/java 100

update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_101/bin/javac 100

Then I execute this two commands and this is the result:

update-alternatives --display java

update-alternatives --display javac

java - auto mode
  link best version is /opt/jdk/jdk1.8.0_101/bin/java
  link currently points to /opt/jdk/jdk1.8.0_101/bin/java
  link java is /usr/bin/java
/opt/jdk/jdk1.8.0_101/bin/java - priority 100
/usr/lib/jvm/jdk1.8.0_101/bin/java - priority 3


javac - auto mode
  link best version is /usr/lib/jvm/jdk1.8.0_101/bin/javac
  link currently points to /usr/lib/jvm/jdk1.8.0_101/bin/javac
  link javac is /usr/bin/javac
/opt/jdk/jdk1.8.0_101/bin/javac - priority 100
/usr/lib/jvm/jdk1.8.0_101/bin/javac - priority 100

After doing all that, when I try java -version this is the result :

root@Debian:/opt/jdk#     java -version
bash: /usr/bin/java: No such file or directory

I add java to path , and I create the java_home:

root@Debian:/opt/jdk# echo $JAVA_HOME 
/opt/jdk/jdk1.8.0_101
root@Debian:/opt/jdk# echo $PATH 
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/jdk/jdk1.8.0_101/bin:/opt/jdk/jdk1.8.0_101/db/bin:/opt/hadoop/sbin:/opt/hadoop/bin

this is the content of /etc/environement :

root@Debian:/opt/jdk# cat /etc/environment
PATH="/opt/jdk/jdk1.8.0_101:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games"
JAVA_HOME="/opt/jdk/jdk1.8.0_101"

When I execute

sudo update-alternatives --config java

I have this result :

root@Debian:/opt/jdk# update-alternatives --config java

There are 2 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status

------------------------------------------------------------

+0 /opt/jdk/jdk1.8.0_101/bin/java 100 auto mode

1 /opt/jdk/jdk1.8.0_101/bin/java 100 manual mode

2 /usr/lib/jvm/jdk1.8.0_101/bin/java 3 manual mode

Press to keep the current choice[+], or type selection number:

the result shows that I'm using /opt/jdk/jdk1.8.0_101/bin/java I don't understand what is the origin of this problem to fix it , please any one have an idea how to fix it ?