Question

If I have a class, let’s say, extended from DialogFragment and define custom constructor for it, why should I define a default one? If I wouldn’t I get the error message if runtime change occurs.

Answer 1

I suspect the problem is that in Java, the compiler creates a parameterless constructor for you unless you specify one yourself. If something within Android requires a parameterless constructor, then either you need to not declare any constructors yourself or you need to explicitly declare a parameterless one.

From section 8.8.9 of the Java Language Spec:

If a class contains no constructor declarations, then a default constructor that takes no parameters is automatically provided:

• If the class being declared is the primordial class Object, then the default constructor has an empty body.
• Otherwise, the default constructor takes no parameters and simply invokes the superclass constructor with no arguments.

Does that make things clear? I don’t know enough about Android to know why you need a parameterless constructor, but presumably it’s so that instances can be created via reflection without specifying any arguments for constructor parameters.