~/.local/jdk-11.0.6/bin/java --version
java 11.0.6 2020-01-14 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.6+8-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.6+8-LTS, mixed mode)
``

~/.local/jdk-11.0.6/bin/java ~/Downloads/i2pinstall_0.9.45.jar
Error: Could not find or load main class .home.user.Downloads.i2pinstall_0.9.45.jar
Caused by: java.lang.ClassNotFoundException: /home/user/Downloads/i2pinstall_0/9/45/jar

java ./i2pinstall_0.9.45.jar
Error: Could not find or load main class ..i2pinstall_0.9.45.jar

dpkg -l | grep java
ii  ca-certificates-java                   20170929~deb9u3                             all          Common CA certificates (JKS keystore)
ii  gir1.2-javascriptcoregtk-4.0:amd64     2.18.6-1~deb9u1                             amd64        JavaScript engine library from WebKitGTK+ - GObject introspection data
ii  java-common                            0.58+deb9u1                                 all          Base package for Java runtimes
ii  javascript-common                      11                                          all          Base support for JavaScript library packages
ii  libatk-wrapper-java                    0.33.3-13+deb9u1                            all          ATK implementation for Java using JNI
ii  libatk-wrapper-java-jni:amd64          0.33.3-13+deb9u1                            amd64        ATK implementation for Java using JNI (JNI bindings)
ii  libgjs0e                               1.46.0-1+b2                                 amd64        Mozilla-based javascript bindings for the GNOME platform
ii  libjavascriptcoregtk-4.0-18:amd64      2.18.6-1~deb9u1                             amd64        JavaScript engine library from WebKitGTK+
user@work 17:41:09 (571) ~/Downloads  $ 
dpkg -l | grep jdk
ii  default-jdk                            2:1.8-58+deb9u1                             amd64        Standard Java or Java compatible Development Kit
ii  default-jdk-headless                   2:1.8-58+deb9u1                             amd64        Standard Java or Java compatible Development Kit (headless)
ii  openjdk-8-jdk:amd64                    8u252-b09-1~deb9u1                          amd64        OpenJDK Development Kit (JDK)
ii  openjdk-8-jdk-headless:amd64           8u252-b09-1~deb9u1                          amd64        OpenJDK Development Kit (JDK) (headless)
ii  openjdk-8-jre:amd64                    8u252-b09-1~deb9u1                          amd64        OpenJDK Java runtime, using Hotspot JIT
ii  openjdk-8-jre-headless:amd64           8u252-b09-1~deb9u1                          amd64        OpenJDK Java runtime, using Hotspot JIT (headless)