subclass

Why doesn't the following work (Python 2.5.2)? >>> import datetime >>> class D(datetime.date): def __init__(self, year): datetime.date.__init__(self, year, 1, 1) >>> D(2008) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: function takes exactly 3 arguments (1 given) I wanted to create a class that was just like datetime.date , but with a different __init__ function. Apparently my function never gets called. Instead the original datetime.date.__init__ is called and fails because that expects 3 arguments and I am passing in one. What's going on here? And is this

I was thinking along the lines of using typeid() but I don't know how to ask if that type is a subclass of another class (which, by the way, is abstract) You really shouldn't. If your program needs to know what class an object is, that usually indicates a design flaw. See if you can get the behavior you want using virtual functions. Also, more information about what you are trying to do would help. I am assuming you have a situation like this: class Base; class A : public Base {...}; class B : public Base {...}; void foo(Base *p) { if(/* p is A */) /* do X */ else /* do Y */ } If this is what

I am trying to create a constructor that takes a field as a parameter, then puts it in a field that is stored in a superclass. Here is the code I am using public crisps(String flavour, int quantity) { this.flavour = super.getFlavour(); this.quantity = quantity; } In the superclass I have initialised the field with private String flavour; and I have an accessor method public String getFlavour() { return flavour; } I am getting an error " flavour has private access in the superclass ", but I believe this shouldn't matter as I am calling the accessor method that returns it to the field? What you

This question already has an answer here: Check if a Class Object is subclass of another Class Object in Java 7 answers In an android app test suite I have a class like this where B is a view: public class A extends B { ... etc... } now I have a list of view objects which may contain A objects but in this case I only care if they're subclasses or "instances of" B . I'd like to do something like: ArrayList<View> viewList = getViews(); Iterator<View> iterator = viewList.iterator(); while (iterator.hasNext() && viewList != null) { View view = iterator.next(); if (view.getClass().isInstance(B

How to I test if a is a subclass of b ? Class<?> a = A.class; Class<?> b = B.class; Are you looking for: Super.class.isAssignableFrom(Sub.class) Rob Hruska If you want to know whether or not a Class extends another, use Class#isAssignableFrom(Class) . For your example, it would be: if(B.class.isAssignableFrom(A.class)) { ... } If you're interested in whether or not an instance is of a particular type, use instanceof : A obj = new A(); if(obj instanceof B) { ... } Note that these will return true if the class/instance is a member of the type hierarchy and are not restrictive to direct