Could not find or load main class 2.lib code example

Example 1: > Task :run FAILED Error: Could not find or load main class Caused by: java.lang.ClassNotFoundException:

Check your build.gradle file and update the application block:

application {
    // Define the main class for the application.
  	// insert the entire name of the class
    mainClassName = 'packageName.MainClass'
}

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