ubuntu18从java8更新到java11

先安装java 11, 再更新软连接

sudo apt update
sudo apt install -y openjdk-11-jdk

1. check java
$which java
/usr/bin/java
$ ls -lrt /usr/bin/java
lrwxrwxrwx 1 root root 22 Aug 31  2021 /usr/bin/java -> /etc/alternatives/java
$ ls -lrt /etc/alternatives/java
lrwxrwxrwx 1 root root 46 May 30 10:23 /etc/alternatives/java -> /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

2. change link path
sudo ln -s -f /usr/lib/jvm/java-11-openjdk-amd64/bin/java /etc/alternatives/java