constructor

问题 Suppose I have one POJO class User with a constuctor public User(int id, String name){...} . But when I instantiate the User object like User u=new User() with no parameter Eclipse gives error like The constructor User() is undefined . But it works fine when I have no parameterized Constructor. Can someone please explain why It requires to define default constructor? 回答1: The default (no-parameter) constructor is ONLY provided if you have provided no others. If you define even a single

问题 Python version: "'2.7.3 (default, Apr 10 2013, 06:20:15) \n[GCC 4.6.3]'" I have this: >>> class testclass1(object): ... pass ... >>> class testclass2(object): ... def __init__(self,param): ... pass ... >>> a = object.__new__(testclass1, 56) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: object.__new__() takes no parameters >>> b = object.__new__(testclass2, 56) >>> b <__main__.testclass2 object at 0x276a5d0> Some more fun! Compare with results of testclass1

问题 I often find myself writing class constructors like this: class foo: def __init__(self, arg1, arg2, arg3): self.arg1 = arg1 self.arg2 = arg2 self.arg3 = arg3 This can obviously become a pain if the number of arguments (and class attributes) gets high. I'm looking for the most pythonic way to loop through the constructor's arguments list and assign attributes accordingly. I'm working with Python 2.7, so ideally I'm looking for help with that version. 回答1: The most Pythonic way is what you've

问题 I'm pretty sure this is a duplicate question, but I've been searching for a while and I didn't get any smarter. Imagine this class: class Entity { public: int x, y; Entity() : x(0), y(0) { } Entity(int x, int y) : x(x), y(y) { } } And here are multiple ways of initializing the class: Entity ent1; Entity ent2(); Entity ent3(1, 2); Entity ent4 = Entity(); Entity ent5 = Entity(2, 3); I also know that's it's possible make an object on the heap memory, but that's not a great mystery to me at this

问题 I'm pretty sure this is a duplicate question, but I've been searching for a while and I didn't get any smarter. Imagine this class: class Entity { public: int x, y; Entity() : x(0), y(0) { } Entity(int x, int y) : x(x), y(y) { } } And here are multiple ways of initializing the class: Entity ent1; Entity ent2(); Entity ent3(1, 2); Entity ent4 = Entity(); Entity ent5 = Entity(2, 3); I also know that's it's possible make an object on the heap memory, but that's not a great mystery to me at this

问题 I'm pretty sure this is a duplicate question, but I've been searching for a while and I didn't get any smarter. Imagine this class: class Entity { public: int x, y; Entity() : x(0), y(0) { } Entity(int x, int y) : x(x), y(y) { } } And here are multiple ways of initializing the class: Entity ent1; Entity ent2(); Entity ent3(1, 2); Entity ent4 = Entity(); Entity ent5 = Entity(2, 3); I also know that's it's possible make an object on the heap memory, but that's not a great mystery to me at this

问题 Is there a way in CXF to generate JAXB classes with full constructors (i.e., with the members of the class as arguments)? 回答1: Use the value-constructor xjc plugin. Maven snippet: <plugin> <groupId>org.apache.cxf</groupId> <artifactId>cxf-codegen-plugin</artifactId> <version>${cxf.version}</version> <executions> <execution> <id>generate-sources</id> <phase>generate-sources</phase> <configuration> <defaultOptions> <extraargs> <extraarg>-xjc-Xvalue-constructor</extraarg> </extraargs> <

问题 so I have a java class called User that contains a constructor like this: public class User extends Visitor { public User(String UName, String Ufname){ setName(UName); setFname(Ufname); } } And then the he problems occur in my other class called Admin: public class Admin extends User { //error "Implicit super constructor User() is undefined for default constructor. Must define an explicit constructor" //public Admin() { } //tried to add empty constructor but error stays there //} public void

问题 I am quite new to C++ and have observed, that the following lines of code act differently MyClass c1; c1.do_work() //works MyClass c2(); c2.do_work() //compiler error c2228: left side is not a class, structure, or union. MyClass c3{}; c3.do_work() //works with a header file as class MyClass { public: MyClass(); void do_work(); }; Can you explain me, what the difference between the three ways of creating the object is? And why does the second way produce a compiler error? 回答1: Ways one and

问题 I am quite new to C++ and have observed, that the following lines of code act differently MyClass c1; c1.do_work() //works MyClass c2(); c2.do_work() //compiler error c2228: left side is not a class, structure, or union. MyClass c3{}; c3.do_work() //works with a header file as class MyClass { public: MyClass(); void do_work(); }; Can you explain me, what the difference between the three ways of creating the object is? And why does the second way produce a compiler error? 回答1: Ways one and