$ sudo apt update
$ sudo apt install openjdk-21-jdk

Package configuration

┌────┤ Daemons using outdated libraries ├─────┐
│                                                        │ 
│                                                        │ 
│ Which services should be restarted?                    │ 
│                                                        │ 
│    [*] chrony.service                                  │ 
│    [ ] dbus.service                                    │ 
│    [ ] getty@tty1.service                              │ 
│    [*] mysql.service                                   │ 
│    [ ] networkd-dispatcher.service                     │ 
│    [*] nginx.service                                   │ 
│    [*] packagekit.service                              │ 
│    [ ] systemd-logind.service                          │ 
│    [*] systemd-resolved.service                        │ 
│    [ ] unattended-upgrades.service                     │ 
│    [ ] user@0.service                                  │ 
│                                                        │ 
│                                                        │ 
│          <Ok>              <Cancel>                    │ 
│                                                        │ 
└────────────────────────────┘ 

# 选择默认

验证信息

$ java --version 

openjdk 21.0.8 2025-07-15
OpenJDK Runtime Environment (build 21.0.8+9-Ubuntu-0ubuntu122.04.1)
OpenJDK 64-Bit Server VM (build 21.0.8+9-Ubuntu-0ubuntu122.04.1, mixed mode, sharing)