看图。
注意事项就是注意一下路径。
update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0_341/bin/java 1
update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0_341/bin/javac 1
update-alternatives --set java /usr/lib/jvm/jdk1.8.0_341/bin/java
update-alternatives --set javac /usr/lib/jvm/jdk1.8.0_341/bin/javac