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I want to make an argument for one of the member functions optional. When no argument is provided, it would use an member variable. However, when I tried to compile it it shows " error: invalid use of non-static data member 'Object::initPos' " Just to isolate the problem, I tried defaulting an int type and it compiled fine. I wonder what is the problem with my code and how I could use a member function as default value. Thank you for your help! Object.h class Object { public: ... void MoveTo(double speed, Point position); protected: Point initPos; Point currPos; }; Object.c void Object::MoveTo

My application is composed by a few activity. Activity A is my main menu with some icons. This Activity can launch depending on which icon you press: Activity B,C,D,E or F. That's fine and really easy, Activity A is the default one. Now, I made an option in preference that allow users to start their favourite activity. Some users will in fact prefer to get directly Activity B for instance. The only way I found a solution was to do this in Activity A This solution is very ugly because Activity A will always launch and close automatically: public void onCreate(Bundle savedInstanceState) { super

I'm currently working on a problem that involves System.Reflection.Emit code generation. I'm trying to figure out what CIL to emit in places where I would use default(SomeType) in C#. I've run a few basic experiments from Visual Studio 11 Beta. JustDecompile shows me the following CIL output for default(bool) , default(string) , and default(int? : .locals init ( [0] bool V_0, [1] string V_1, [2] valuetype [mscorlib]System.Nullable`1<int32> V_2 ) // bool b = default(bool); ldc.i4.0 stloc.0 // string s = default(string); ldnull stloc.1 // int? ni = default(int?); ldloca.s V_2 initobj valuetype

I have a Map<String, List<String>> in my code, where I'd avoid potential null pointers if the map's #get() method returned an empty list instead of null. Is there anything like this in the java API? Should I just extend HashMap ? Stephen C @Jon's answer is a good way to do what you are asking directly. But is strikes me that what you might be trying to implement is a "multimap"; i.e. a mapping from a key to a collection of values. If that is the case, then you should also look at the multimap classes in Guava or Apache commons collections. Look at: the com.google.common.collect.Multimap

If I use a migration to update a database, and I add an integer field like this: t.integer :foo :default => 0, :null => false What is the default state of existing and new records in the database? I hoping the answer is: - Both will read back foo as 0. Is default => 0 necessary, if I have :null => false? Just trying to understand the difference between the two... :null => false tells your database not to accept NULL values. :default => 0 does two things: Tell your database to use '0' as the default value when NULL or nothing is specified in a query. Tell rails to use '0' as a default value

What is the best way to set a default value for a foreign key field in a model? Suppose I have two models, Student and Exam with student having exam_taken as foreign key. How would I ideally set a default value for it? Here's a log of my effort class Student(models.Model): .... ..... exam_taken = models.ForeignKey("Exam", default=1) Works, but have a hunch there's a better way. def get_exam(): return Exam.objects.get(id=1) class Student(models.Model): .... ..... exam_taken = models.ForeignKey("Exam", default=get_exam) From here , but fails with tables does not exist error while syncing. Any

Is there any way to require that a class have a default (no parameter) constructor, aside from using a reflection check like the following? (the following would work, but it's hacky and reflection is slow) boolean valid = false; for(Constructor<?> c : TParse.class.getConstructors()) { if(c.getParameterTypes().length == 0) { valid = true; break; } } if(!valid) throw new MissingDefaultConstructorException(...); You can build an Annotation processor for that. Annotation Processors are compiler plugins that get run at compile time. Their errors show up as compiler errors, and may even halt the

Can the (implicit) default copy constructor be called for a class that has already user-defined constructor but that is not the copy constructor ? If it is possible then, suppose we define the copy constructor for the class explicitly , now can the (implicit)default constructor be called? James Kanze First, let's clarify our vocabulary a bit. A default constructor is a constructor which can be called without any arguments. A copy constructor is a constructor which can be called with a single argument of the same type. Given this, a "default copy constructor" would be a constructor with a