sudo update-alternatives --config java update-alternatives: error: no alternatives for java
The installed java versions need to be added to update-alternatives:
adding jdk-11 with 10 priority :
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-11-openjdk-amd64/bin/java 10
adding jdk-15 with 20 priority (suppose you have extracted the tarball to /usr/lib/jvm/ directory. In your case replace /usr/lib/jvm/jdk-15.0.2/bin/java with /usr/local/bin/jdk-15.0.2/bin/java)
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-15.0.2/bin/java 20
Check it:
sudo update-alternatives --list java /usr/lib/jvm/java-11-openjdk-amd64/bin/java /usr/lib/jvm/jdk-15.0.2/bin/java
and
sudo update-alternatives --config java
sample output:
There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib/jvm/jdk-15.0.2/bin/java 20 auto mode 1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 10 manual mode 2 /usr/lib/jvm/jdk-15.0.2/bin/java 20 manual mode Press <enter> to keep the current choice[*], or type selection number:
Check the java version, in the above example the default version is jdk-15:
java --version openjdk 15.0.2 2021-01-19 OpenJDK Runtime Environment (build 15.0.2+7-27) OpenJDK 64-Bit Server VM (build 15.0.2+7-27, mixed mode, sharing)