Error: Could not find or load main class mina.calc.MinaCalculator in module mina code example

Example 1: Error: Could not find or load main class mina.calc.MinaCalculator in module mina

//You must change your class name

Example 2: Error: Could not find or load main class -Djava.library.path=.home.hdoop.hadoop-3.3.0.lib.native

Sounds silly, but if you've copied .bashrc lines from somewhere
check that the quotation marks are like this:
    export HADOOP_OPTS="-Djava.library.path=$HADOOP_HOME/lib/native"
and not like this
    export HADOOP_OPTS=”-Djava.library.path=$HADOOP_HOME/lib/native”

...took me some time