[GROOVY-7246] Access modifiers behave differently in Groovy when compared to Java.

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.3.9
• Fix Version/s: 2.3.9
• Labels: usertask
• Environment: 64-bit Windows 7
• Assignee: Unassigned
• Reporter: Todd Gerspacher
• Created: 11/Jan/15 08:30
• Updated: 21/Jan/15 15:26
• Resolved: 12/Jan/15 14:18

Description

I know there's already been several JIRA tickets that have been created concerning how private fields and methods aren't really private in Groovy.

See Also: GROOVY-3010

But it seems like Groovy doesn't respect the access restrictions of any of the access modifiers. Last year I did a blog post on Java's access modifiers and recently I did the same experiment but with Groovy this time. I've listed below all the classes that I used. I only changed the access modifiers for the name field and speak method of the Earthling class.

Earthling.groovy

package Earth;

// access modifiers will be changed for this class
public class Earthling {
   public String name = "Bob";
 
   public void speak() {
      System.out.println("Hello.");
   }
}

Man.groovy

package Earth;

// subclass, same package
public class Man extends Earthling {
   public Man() {
      System.out.println("name = " + name);
      speak();
   }
 
   public static void main(String[] args) {
      new Man();
   }
}

Dog.groovy

package Earth;

// non-subclass, same package 
public class Dog {
   public Dog() {
      Earthling earthling = new Earthling();
      System.out.println("earthling.name = " + earthling.name);
      earthling.speak();
   }
 
   public static void main(String[] args) {
      new Dog();
   }
}

Explorer.groovy

package Mars;
 
import Earth.Earthling;

// subclass, different package
public class Explorer extends Earthling {
   public Explorer() {
      System.out.println("name = " + name);
      speak();
   }
 
   public static void main(String[] args) {
      new Explorer();
   }
}

Martian.groovy

package Mars;
 
import Earth.Earthling;

// non-subclass, different package
public class Martian {
   public Martian() {
      Earthling earthling = new Earthling();
      System.out.println("earthling.name = " + earthling.name);
      earthling.speak();
   }
 
   public static void main(String[] args) {
      new Martian();
   }
}

When I did this little experiment in Java, I got the following results. The cells marked with 'J' indicates when I was able to access Earthling's name field and speak method.

	public	protected	(no modifier)	private
Subclass, Same Package	J	J	J
Non-Subclass, Same Package	J	J	J
Subclass, Different Package	J	J
Non-Subclass, Different Package	J

When I did the same thing in Groovy, however, I got much different results. Note I've marked the cells with 'G' this time.

	public	protected	(no modifier)	private
Subclass, Same Package	G	G	G	throws exception
Non-Subclass, Same Package	G	G	G	G
Subclass, Different Package	G	G	G	throws exception
Non-Subclass, Different Package	G	G	G	G

You'll notice that pretty much every class can access everything. The only issues occur when you use the private access modifier and you try to access the field or method from a subclass. But instead of throwing a compiler error, like Java does, Groovy throws runtime exceptions. Specifically,

groovy.lang.MissingPropertyException: No such property: name

And if you comment out the statement that references the name field...

Man.groovy

package Earth;

// subclass, same package
public class Man extends Earthling {
   public Man() {
      // System.out.println("name = " + name);
      speak();
   }
 
   public static void main(String[] args) {
      new Man();
   }
}

...you'll get a different exception.

groovy.lang.MissingMethodException: No signature of method: Earth.Man.speak