Before I start, please note that the JDK also contains the JRE within it.

Method 1:

To install the openJDK JDK and JRE 8 use (replace 8 with the version you want, such as 7 or 6):

sudo apt-get install openjdk-8-jdk

Method 2:

If you instead want to install the official Oracle JDK and JRE and definitely want to install through apt-get then do (you can replace the 8 with other versions such as 9, or 7):

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer

Method 3:

Or if you want to install the official Oracle Java version manually:

1. Go here and click the download button:

   

2. Select the Accept License Agreement radio button (once you have read the license agreement).

3. Select the file you want to download, if you are running on a 32-bit machine click jdk-[javaversion]-linux-i586.tar.gz ([javaversion] replaced with the Java version, such as 8u60), if 64-bit then jdk-[javaversion]-linux-x64.tar.gz.

4. Launch Terminal (CTRL + ALT + T), then cd to the directory where you downloaded the file to (probably ~/Downloads), and run tar -xvf /path/to/file.tar.gz to unpack that archive into the directory the file is in, you may then move that unpacked archive into a desired location, such as the /opt directory (storing executable files in your home directory is a security risk).

5. Once you have done the above you may delete the original .tar.gz file, and then open up your ~/.bashrc file in a desired file editor such as gedit or vim, I will be using vim in this example (install it with sudo apt-get install vim if it is not already installed). So run vim ~/.bashrc and then insert two new lines at the bottom of the file which read (that is with /path/to/unpacked/archive replaced with the path to the archive you just unpacked):

   JAVA_HOME=/path/to/unpacked/archive
   export PATH=$PATH:$JAVA_HOME/bin
   

6. Either restart Terminal or run source ~/.bashrc to start using the new .bashrc file.

   Note: With this method you will have to carry on doing this every time there is a new Java version released which it will not notify you about.

Using export JAVA_HOME=/usr/share/java will point to the bin folder. This is just a symbolic link to the actual installation folder.

You should make it if you update it to export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64.

Note you should use the root folder.

try using this command in the terminal:

sudo apt install default-jre

then you can try using:

java -version

to check version