Your class is in package projectname, so the code is looking for the resource file projectname/config.properties, but the file is not there.

To look for resource file config.properties, use:

getClass().getResource("/config.properties");

as documented in the javadoc of getResource().

And remember, the resource may not be a file on the file system, so don't use e.g. File to access it. To read the content of the resource, use getResourceAsStream() instead.

You should use Java resource loading system. This is not depending on your IDE. Once you have marked a folder as resource folder in IntelliJ, it is available in your code as via resource loader.

Just move the file directly to the project folder which calls Java (and something under the blue-blurred stripe you made :P).

If that doesn't help, then move the test123.txt file to FirstJavaProgram directory.

You can also change filename to one of these:

1. src/test123.txt

2. FirstJavaProgram/src/test123.txt

I am not sure which one will be fine in your case.

Try the next:

ClassLoader classloader = Thread.currentThread().getContextClassLoader();
InputStream is = classloader.getResourceAsStream("test.csv");

If the above doesn't work, various projects have been added the following class: ClassLoaderUtil¹ (code here).²

Here are some examples of how that class is used:

src\main\java\com\company\test\YourCallingClass.java
src\main\java\com\opensymphony\xwork2\util\ClassLoaderUtil.java
src\main\resources\test.csv

// java.net.URL
URL url = ClassLoaderUtil.getResource("test.csv", YourCallingClass.class);
Path path = Paths.get(url.toURI());
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);

// java.io.InputStream
InputStream inputStream = ClassLoaderUtil.getResourceAsStream("test.csv", YourCallingClass.class);
InputStreamReader streamReader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
BufferedReader reader = new BufferedReader(streamReader);
for (String line; (line = reader.readLine()) != null;) {
    // Process line
}

Notes

1. See it in The Wayback Machine.
2. Also in GitHub.