// LISTING 8.1. Przełączanie wersji JDK i JRE w systemie Linux

// 1. Przełączanie JDK w terminalu.
sudo update-alternatives --config javac

// 2. Wybór wersji JDK i kliknięcie Enter.
There are 2 choices for the alternative javac (providing /usr/bin/javac).
    Selection    Path    Priority    Status
------------------------------------------------------------
* 0    /usr/lib/jvm/java-11-openjdk-amd64/bin/javac    1111    auto mode
  1    /usr/lib/jvm/java-11-openjdk-amd64/bin/javac    1111    manual mode
  2    /usr/lib/jvm/java-8-openjdk-amd64/bin/javac     1081    manual mode
Press <enter> to keep the current choice[*], or type selection number: 2

// 3. Przełączenie JRE w terminalu.
sudo update-alternatives --config java

// 4. Wybór wersji JRE i kliknięcie Enter.
There are 2 choices for the alternative java (providing /usr/bin/java).
    Selection    Path    Priority    Status
------------------------------------------------------------
  0    /usr/lib/jvm/java-11-openjdk-amd64/bin/java    1111    auto mode
* 1    /usr/lib/jvm/java-11-openjdk-amd64/bin/java    1111    manual mode
  2    /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081    manual mode
Press <enter> to keep the current choice[*], or type selection number: 2