inheritance

问题 I have created a Base class like this: `namespace XXX.Screens { public partial class Settings_screen_BASE : PhoneApplicationPage { public static readonly bool DEBUG = true; public Settings_screen_BASE() { if (DEBUG) Debug.WriteLine(this.GetType() + "->" + System.Reflection.MethodBase.GetCurrentMethod().Name); InitializeComponent(); if (DEBUG) Debug.WriteLine(this.GetType() + "<-" + System.Reflection.MethodBase.GetCurrentMethod().Name); } } }` And this child class: namespace XXX.Screens {

问题 I have two questions regarding the behavior of running the below code. Why is __new__ even being called without instantiating an object? I thought __new__ controlled the creation of a new instance . Next, why does delattr raise an AttributeError when hasattr returns True for size ? class ShapeBase(type): def __new__(cls, name, bases, attrs): rv = super(ShapeBase, cls).__new__(cls, name, bases, attrs) parents = [base for base in bases if isinstance(base, ShapeBase)] # don't do anything unless

问题 class A { public A() { System.out.println("Constructor A"); } } class B extends A { public B() { System.out.println("Constructor B"); } } class C extends B { public C() { System.out.println("Constructor C"); } public static void main(String[] args) { C c = new C(); } } When running the code then it calls all constructor but needs to call only child constructor. output like only print Constructor C 回答1: Like the comments and the other answer already said, this is explicitly impossible . If a

问题 I want to do something like the following: class A[T] (_arr: Array[T]) { var arr = _arr } class C { def foo[T <: A[_]](a: Array[T]){ var ele1 = a(0) var ele2 = a(1) for(i <- 0 until ele1.arr.length) { val temp = ele1.arr(i) ele1.arr(i) = ele2.arr(i) ele2.arr(i) = temp } } } But I get the following compiler error: <console>:15: error: type mismatch; found : temp.type (with underlying type Any) required: _$1 ele2.arr(i) = temp ^ I'm not sure why ele1.arr(i) = ele2.arr(i) would work and ele2.arr

问题 I want to do something like the following: class A[T] (_arr: Array[T]) { var arr = _arr } class C { def foo[T <: A[_]](a: Array[T]){ var ele1 = a(0) var ele2 = a(1) for(i <- 0 until ele1.arr.length) { val temp = ele1.arr(i) ele1.arr(i) = ele2.arr(i) ele2.arr(i) = temp } } } But I get the following compiler error: <console>:15: error: type mismatch; found : temp.type (with underlying type Any) required: _$1 ele2.arr(i) = temp ^ I'm not sure why ele1.arr(i) = ele2.arr(i) would work and ele2.arr

问题 I'm having a Scala trait A with an abstract method trait A[T] { def self: T } Now it happened me that I want to extends a Java class not under my control with a field with the same name: public class B<T> { protected T self; } I'd like to have a class C defined like class C[T] extends B[T] with A[T] { override def self: T = /* the field `self` of `B` ??? */ } Is it possible to access the field B.self somehow so that it doesn't resolve to the method A.self instead? Is it even possible to have

问题 OK, so, I've asked about this before. Ideally I'm looking for a general answer that will help me understand how to specify types consistently, but in lieu of that, I'll settle for how to solve specific problems. So far each solution seems to bring 3 more issues, I'm trying to avoid putting an entire application here but my goal is to find a way to refer to the type of a recursively parameterized trait type from anywhere, in a useful way, in a non-trivial program, where values of that trait

问题 Another way to ask the same question is, given 2 classes A and B, is it synonymous to say: "Object A can be cast into B" and "Object A is a descendant of B"? Thanks, JDelage Edit: Clarified the question to make it clearer that both A and B are classes. 回答1: " Java - Can you cast an object into a class it doesn't extend? " - No, you can't. " Basically, is it synonymous to say: "Object A can be cast into B" and "Object A is a direct descendant of B"? " - Yes. Plus in the case when A is of a

问题 Another way to ask the same question is, given 2 classes A and B, is it synonymous to say: "Object A can be cast into B" and "Object A is a descendant of B"? Thanks, JDelage Edit: Clarified the question to make it clearer that both A and B are classes. 回答1: " Java - Can you cast an object into a class it doesn't extend? " - No, you can't. " Basically, is it synonymous to say: "Object A can be cast into B" and "Object A is a direct descendant of B"? " - Yes. Plus in the case when A is of a

问题 I implement the Eric Meyer's reset.css in my website, and works great, but it was a little problem. As this a CMS users are free to format the content of their articles as they want and the reset CSS resets the formatting of their text. Any ideas how we can prevent reset.css inheritance to propagate to the dynamic content? All you input is more than welcome. 回答1: It will always propagate (that's kind of the point of reset.css :)), but if you're not already doing so, you should of course make