Why is error checking not working?

I have two separate projects where error checking isn't working, both were cloned from previous repos. 

In the first case, it *should* be flagging an error but it doesn't. I'm trying to assign an int to a String property. But it doesn't show anything wrong. (The compiler complains though when I run the project):

In the second case, it's complaining that there's no such thing as a Long, when that's built in to Java and the compiler runs everthing fine:

How do I debug these problems? They seem to be related.

Thanks.