inheritance

问题 I have a base class, say BassClass , with some fields, which I made them protected, and some pure virtual functions. Then the derived class, say DerivedClass , like class DerivedClass : public BassClass . Shouldn't DerivedClass inherit the protected fields from BassClass? When I tried to compile the DerivedClass, the compiler complains that DerivedClass does NOT have any of those fields, what is wrong here? thanks 回答1: If BassClass (sic) and DerivedClass are templates, and the BassClass

问题 I have a base class, say BassClass , with some fields, which I made them protected, and some pure virtual functions. Then the derived class, say DerivedClass , like class DerivedClass : public BassClass . Shouldn't DerivedClass inherit the protected fields from BassClass? When I tried to compile the DerivedClass, the compiler complains that DerivedClass does NOT have any of those fields, what is wrong here? thanks 回答1: If BassClass (sic) and DerivedClass are templates, and the BassClass

问题 How do I inherit constructors from a template base class without repeating the template arguments (and without using macros): For example, this does not work (using GCC 4.8): template <typename T> struct base {}; template <typename U> struct derived : base<U> { using base::base; }; It does work if I repeat the template arguments of the base class: template <typename T> struct base {}; template <typename U> struct derived : base<U> { using base<U>::base; }; The problem is that "U" might be

问题 public class Main { public static void main(String[] args) { System.out.println(B.x); } } class A { public static String x = "x"; } class B extends A { static { System.out.print("Inside B."); } } Question: Why output will be: x . But not: Inside B.x 回答1: The reference to B.x issues the following bytecode: getstatic #3 <Field int B.x> According to Java Virtual Machine Spec The Java virtual machine instructions anewarray, checkcast, getfield, getstatic , instanceof, invokedynamic,

问题 Apart from the inheritance aspect, is there a difference between the following class templates: 1| trait TraitA extends TraitB 2| trait TraitA { self: TraitB => } I would like to split responsibilities between TraitA and TraitB but the former cannot function without the latter. How would you express this intent? To me solution [2] would be the more natural approach. However I do not want to put the burden on implementers mixing in what needs to be mixed in anyway. 回答1: My preference is

问题 Can have an abstract class implementing all of its methods -- with no abstract methods in it. Eg.: public abstract class someClass { int a; public someClass (int a) { this.a = a; } public void m1 () { /* do something */ } private void m2 () { /* do something else */ } } What's the advantage, if any, of having such an abstract class compared to having the same class as a concrete one instead? One i can think of is that, when i declare it as abstract, it won't be instantiated. however, i can

问题 In the following code- class Mammal { String name = "furry "; String makeNoise() { return "generic noise"; } } class Zebra extends Mammal { String name = "stripes "; String makeNoise() { return "bray"; } } public class ZooKeeper { public static void main(String[] args) { new ZooKeeper().go(); } void go() { Mammal m = new Zebra(); System.out.println(m.name + m.makeNoise()); Zebra z = new Zebra(); System.out.println(z.name + z.makeNoise()); } } Both objects ( m and z ), if I see in debug

问题 In the following code- class Mammal { String name = "furry "; String makeNoise() { return "generic noise"; } } class Zebra extends Mammal { String name = "stripes "; String makeNoise() { return "bray"; } } public class ZooKeeper { public static void main(String[] args) { new ZooKeeper().go(); } void go() { Mammal m = new Zebra(); System.out.println(m.name + m.makeNoise()); Zebra z = new Zebra(); System.out.println(z.name + z.makeNoise()); } } Both objects ( m and z ), if I see in debug

问题 Possible Duplicate: To get parent class using Reflection on C# I am trying to find an easy way of getting the inheritance tree of a certain type using reflection in C#. Let's say that I have the following classes; public class A { } public class B : A { } public class C : B { } How do I use reflection upon type 'C' to determine that its superclass is 'B', who in turn comes from 'A' and so on? I know that I can use 'IsSubclassOf()', but let's assume that I don't know the superclass that I am

问题 I was looking at a perf benchmark of Object.keys + forEach vs for-in with normal objects. This benchmark shows that Object.keys + forEach is 62% slower than the for-in approach. But what if you don't want to get the inherited properties ? for-in includes all non-native inherited objects, so we'll have to use hasOwnProperty to check. I tried to make another benchmark here doing exactly that. But now the for-in approach is 41% slower than Object.keys + forEach . update The above test was done