Why only 1 public class in Java file

Question

In any Java file, why can we have only one public class whose name is same as the Java file name?

Answer 1

It forces all Java code to be organized in a certain way, which in the long run helps improve code readability.

The Java designers chose a strict approach that enforces their idea of good design practices, and this is part of that theme. Contrast that with the anything-goes attitude in Perl.