Why make a method volatile in java?

Question

Why would a method be made volatile? How does making a method volatile change the method's behavior?

Edit: I did a toString() on a Method object returned by a class object (Java Reflection). The return string had a volatile modifier against the method name along with public visibility and void return type. Research yielded only information on volatile for properties. This is why I asked this question.

The method declaration was:

public volatile org.osmdroid.api.IGeoPoint org.osmdroid.views.MapView.getMapCenter()

Code for the Reflection Method:

public static class Test {
    public static void showMethods(Object target) {
        Class<?> clazz = target.getClass();
        for (Method method : clazz.getMethods()) {
            if (method!=null) {
                System.out.println(method.toString());
            }
        }
    }
}

Method invocation:

Test.showMethods(mapView);

Answer 1

I strongly suspect that what you're seeing is a side-effect of the fact that the JLS defines the following bit for fields:

public static final int VOLATILE = 0x00000040;

and the following bit for methods:

static final int BRIDGE = 0x00000040;

Note that they have the same value (the same bit has a different meaning for methods and fields).

If you call e.g. Modifier.toString(int) without, as the documentation suggests:

Note that to perform such checking for a known kind of entity, such as a constructor or method, first AND the argument of toString with the appropriate mask from a method like constructorModifiers or methodModifiers.

then you'll get inappropriate output (including bridge methods, autogenerated for e.g. covariant return type, showing up as 'volatile').

At least the current OpenJDK Method.toString() filters this out; if yours isn't, perhaps you're using a different or older version of the JDK which doesn't do this correctly.

Answer 2

You can't. volatile is only a valid modifier for a field.