Firstly, Check whether your environment has already installed Java or not:
[Ubuntu: ~]$apt list --installed | grep -i "jdk"
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
openjdk-8-jdk-headless/focal-updates,focal-security,now 8u292-b10-0ubuntu1~20.04 amd64 [installed,automatic]
openjdk-8-jdk/focal-updates,focal-security,now 8u292-b10-0ubuntu1~20.04 amd64 [installed]
openjdk-8-jre-headless/focal-updates,focal-security,now 8u292-b10-0ubuntu1~20.04 amd64 [installed,automatic]
openjdk-8-jre/focal-updates,focal-security,now 8u292-b10-0ubuntu1~20.04 amd64 [installed,automatic]
Since openjdk-8-jdk/jre is too old, uninstall the all old openjdk/jre:
[Ubuntu: ~]$sudo apt --purge remove openjdk-8-jdk
[Ubuntu: ~]$sudo apt --purge remove openjdk-8-jre
[Ubuntu: ~]$sudo apt --purge remove openjdk-8-jdk-headless
[Ubuntu: ~]$sudo apt --purge remove openjdk-8-jre-headless
...
Install jdk as follows:
[Ubuntu: ~]$sudo apt install default-jdk
Check the installed version:
[Ubuntu: ~]$java --version
openjdk 11.0.11 2021-04-20
OpenJDK Runtime Environment (build 11.0.11+9-Ubuntu-0ubuntu2.20.04)
OpenJDK 64-Bit Server VM (build 11.0.11+9-Ubuntu-0ubuntu2.20.04, mixed mode, sharing)
For setting JAVA_HOME, you need to make sure where the jdk/jre is installed by apt.
[Ubuntu: ~]$sudo update-alternatives --list java
/usr/lib/jvm/java-11-openjdk-amd64/bin/java
/usr/lib/jvm/java-11-openjdk-amd64 is JAVA_HOME path. Because you already got the path where JDK has been installed as the above, set JAVA_HOME and PATH:
[Ubuntu: ~]$echo 'export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64' >> ~/.bashrc
[Ubuntu: ~]$echo 'PATH=$PATH:$JAVA_HOME/bin' >> ~/.bashrc
[Ubuntu: ~]$grep -i java ~/.bashrc
export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
PATH=$PATH:$JAVA_HOME/bin
Apply the path:
[Ubuntu: ~]$source ~/.bashrc
[Ubuntu: ~]$env | grep -i "java"
JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
...
:/usr/lib/jvm/java-11-openjdk-amd64/bin