I think Java is simple because it’s small. There are only 50 keywords and ~40 operators (many of which are variations). As a comparison C# has 102 [1] keywords. Java code is generally easy to understand assuming some familiarity with other languages. There aren’t many weird symbols or constructs. There are very few exceptions to the basic rules of Java. It just does what you’d expect most of the time. Java feels like a lowest common denominator language— a kind of average of everything else.

This “simpleness” is part of what makes Java not easy. It is not very expressive. Java (outside of memory management) does not give the programmer a lot of help. You have to explain things to it in excruciating detail, being very specific and never leaving anything out or the compiler will complain.

The lack of expressiveness makes some things really hard. Just look at the number of dependency injection frameworks that exist for Java. Or logging frameworks.

At a certain point of project complexity everyone ends up fighting their language. It feels that with Java that point comes early then most others. But cleverly I think it comes after a level of complexity that most people end up hitting in enterprisy CRUD apps and that’s a big part of why Java is so popular.

[1] https://stackoverflow.com/a/4980785/858463