我正在尝试在需要 openjdk-6-jre 和 openjdk-7-jre 的 Ubuntu 上下载 XDM（xtreme 下载管理器）。但我无法安装它：
sudo apt-get install openjdk-7-jre
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package openjdk-7-jre 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 'openjdk-7-jre' has no installation candidate
我有 Java 版本 10
java --version
openjdk 10.0.2 2018-07-17
OpenJDK Runtime Environment (build 10.0.2+13-Ubuntu-1ubuntu0.18.04.2)
OpenJDK 64-Bit …