The following module is compiled fine while as it should not because no "requires jdk.desktop" is specified.

===== src/module-info.java =====
module test_completeness @ 1.0 {
  requires jdk.base;

  class test.completeness.desktop.Desktop;
}


===== src/test/completeness/desktop/Desktop.java =====
package test.completeness.desktop;

public class Desktop {
   public static void main(String[] args) {
      System.out.println("Hey");

      { javax.swing.SpringLayout.Constraints obj; }
   }
}

=====
Then I compile it and run as
> ${JAVA_HOME}/bin/javac -d modules -modulepath modules -sourcepath src `find src/ -name *.java`
> ${JAVA_HOME}/bin/jmod install modules/src/ -L mlib test_completeness
> ${JAVA_HOME}/bin/java -L mlib -m test_completeness