我已经有java8工作,但是当我尝试安装java9时,这就是每次都会发生的事情：

sudo apt-get install oracle-java9-installer

Reading package lists… Done Building dependency tree Reading
state information… Done Package oracle-java9-installer is not
available, but is referred to by another package. This may mean that
the package is missing, has been obsoleted, or is only available from
another source

E: Package ‘oracle-java9-installer’ has no installation candidate

解决方法:

做

sudo apt install default-jre default-jdk