How do I identify immutable objects in Java

Question

In my code, I am creating a collection of objects which will be accessed by various threads in a fashion that is only safe if the objects are immutable. When an attempt is m

Answer 1

Try this:

public static boolean isImmutable(Object object){
    if (object instanceof Number) { // Numbers are immutable
        if (object instanceof AtomicInteger) {
            // AtomicIntegers are mutable
        } else if (object instanceof AtomicLong) {
            // AtomLongs are mutable
        } else {
            return true;
        }
    } else if (object instanceof String) {  // Strings are immutable
        return true;
    } else if (object instanceof Character) {   // Characters are immutable
        return true;
    } else if (object instanceof Class) { // Classes are immutable
        return true;
    }

    Class objClass = object.getClass();

    // Class must be final
    if (!Modifier.isFinal(objClass.getModifiers())) {
            return false;
    }

    // Check all fields defined in the class for type and if they are final
    Field[] objFields = objClass.getDeclaredFields();
    for (int i = 0; i < objFields.length; i++) {
            if (!Modifier.isFinal(objFields[i].getModifiers())
                            || !isImmutable(objFields[i].getType())) {
                    return false;
            }
    }

    // Lets hope we didn't forget something
    return true;
}