inheritance

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Why doesn’t Java allow generic subclasses of Throwable? I'm trying to make a regular RuntimeException inside a generic class like this: public class SomeGenericClass<SomeType> { public class SomeInternalException extends RuntimeException { [...] } [...] } This piece of code gives me an error on the word RuntimeException saying The generic class SomeGenericClass<SomeType>.SomeInternalException may not subclass

问题 I have a question about the basics of java. I have the s attribute in each class. The value of s gotten by the instance of the class is different when I use the accessor (getS()). Is there a rule for this case? The output of the main is : x.s = One x.getS() = Three The classes definition : package com; import com.Test1.A; import com.Test1.B; public class Test1 { public static class A { public static String s = "One"; public int x = 10; public String getS() { return this.s; } } public static

问题 I have a question about the basics of java. I have the s attribute in each class. The value of s gotten by the instance of the class is different when I use the accessor (getS()). Is there a rule for this case? The output of the main is : x.s = One x.getS() = Three The classes definition : package com; import com.Test1.A; import com.Test1.B; public class Test1 { public static class A { public static String s = "One"; public int x = 10; public String getS() { return this.s; } } public static

问题 This code compiles with MSVC 2015, but doesn't compile with Clang 5.0.0 (trunk 304874): template <typename T> struct Base { T data; }; template <typename T> struct Derived : Base<T> { auto getData() const { return data; } }; Replacing data with this->data in Derived::getdata() makes Clang happy. Which compiler is correct according to the C++ standard? Must this-> be used in template code to access an identifier of a base class? 回答1: Clang is correct. $17.6.2/3 Dependent names [temp.dep] In

问题 This question already has answers here : How to call a parent method from child class in javascript? (8 answers) Closed 10 days ago . class Parent { constructor(x) { this.x = x; } present() { return `I have a ${this.x}`; } } class Child extends Parent { constructor(x, y) { super(x); this.y = y; } present() { return `${super.present()}, it is a ${this.y}`; } } child = new Child("Tinggu", "Winggu"); console.log(child.present()); // invokes the child version How would I invoke the parent's

问题 This question already has answers here : How to call a parent method from child class in javascript? (8 answers) Closed 10 days ago . class Parent { constructor(x) { this.x = x; } present() { return `I have a ${this.x}`; } } class Child extends Parent { constructor(x, y) { super(x); this.y = y; } present() { return `${super.present()}, it is a ${this.y}`; } } child = new Child("Tinggu", "Winggu"); console.log(child.present()); // invokes the child version How would I invoke the parent's

问题 Consider the following example: class A: def m(): pass class B(A): pass And the following terminal output: >>> b = B() >>> b.m <bound method A.m of <__main__.B object at 0x000001EFFF24C748>> >>> super(b.__class__, b).m <bound method A.m of <__main__.B object at 0x000001EFFF24C748>> >>> b.m is super(b.__class__, b).m False >>> b.m == super(b.__class__, b).m True Why are they equal but not identical? Is a copy of the method made when it is inherited? Are there better ways to test whether a

问题 I would like to override a virtual function in a template-derived class. However, I would like to use the derived class as return type. Here is the corresponding code: class Abstract { public: virtual Abstract* allocate() const = 0; }; template <typename Derived> class Base : public Abstract { public: Derived* allocate() const override { return new Derived; } }; class Concrete : public Base<Concrete> { public: }; int main() { Concrete c; delete c.allocate(); } Unfortunately, my compiler does

问题 I would like to override a virtual function in a template-derived class. However, I would like to use the derived class as return type. Here is the corresponding code: class Abstract { public: virtual Abstract* allocate() const = 0; }; template <typename Derived> class Base : public Abstract { public: Derived* allocate() const override { return new Derived; } }; class Concrete : public Base<Concrete> { public: }; int main() { Concrete c; delete c.allocate(); } Unfortunately, my compiler does

问题 I coworker of mine told me that it was possible to convert a List<BaseClass> to a List<DerivedClass> (they didn't show me a working example). I didn't think it was possible to convert a parent class into a child class (I do know however that it is possible to do it the other way around). I've seen several related questions with people saying it can't be done and people saying it can - none of the proposed solutions have worked for me at all. I always get a: System.InvalidCastException. Unable