Why is javac not complaining about more than one public class per file?

Question

Here's my sample class, that compiles (and runs) with version 1.6.0_14 of Java:

import java.util.List;
import java.util.ArrayList;

public class Sample {
  List<InnerSample> iSamples;

  public Sample() {
    iSamples = new ArrayList<InnerSample>();
    iSamples.add(new InnerSample("foo"));
    iSamples.add(new InnerSample("bar"));
  }

  public static void main(String[] args) {
    System.out.println("Testing...");
    Sample s = new Sample();
    for (InnerSample i : s.iSamples) {
      System.out.println(i.str);
    }
  }

  public class InnerSample {
    String str;
    public InnerSample(String str) {
      this.str = str;
    }
  }
}

I know that you're supposed to only have one public class per file in Java, but is this more of a convention than a rule?

Answer 1

You cannot have more than one top level public class.

Nested/inner classes/interfaces/enums/@annotations don't count.

Answer 2

In your example, InnerSample is an "inner" class. An inner class MUST be inside another class (and thus, inside the outer class' source file).

Answer 3

You're not allowed to have more than one top-level class per file. InnerSample is an inner class.

This is an example of what is prohibited in a single file:

public class Sample {

}

public class Sample2 {

}

See JLS §7.6.