Summary

Correct Java source launcher to reject programs with a private no-arg constructor.

Problem

The behaviour of the java launcher for the following HelloWorld.java program defining a private no-arg constructor is different when run in source and class mode:

class HelloWorld {
  private HelloWorld() {}
  void main() { IO.println("Hello world"); }
}

$ java HelloWorld.java

Hello world

javac HelloWorld.java | java HelloWorld

Error: no non-private zero argument constructor found in class HelloWorld
remove private from existing constructor or define as:
   public HelloWorld()

Solution

Perform same check as in class launch mode and fail with a similar error message.

Specification

The check in class mode, found in LauncherHelper.java, reads:

    if (Modifier.isPrivate(constructor.getModifiers())) {
        throw new Fault(Errors.CantAccessConstructor(mainClassName));
    }

That check should be adopted and applied to SourceLauncher.java as:

    if (Modifier.isPrivate(constructor.getModifiers())) {
        throw new Fault(Errors.CantUsePrivateConstructor(mainClassName));
    }