class-constructors | 易学教程

Laravel command cannot call $this->info() in child class

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问题 I'm just starting out with the basic concepts OO in PHP, Foo.php class Foo extends Command { public function __construct() { parent::__construct(); } public function fire() { $bar = new Bar(); } } Bar.php class Bar extends Foo { public function __construct() { parent::__construct(); $this->info('Bar'); } } When I run Foo::fire() it gives: Call to undefined method Foo::__construct() . But Foo clearly has a constructor, what am I doing wrong? Another thing I suspect is that it might be a

Why is my constructor not getting called?

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问题 I'm trying to add some records to a SQLite table, but LogCat is telling me the table does not exist. And DDMS shows that, yes, that table is not being/has not been created. Yet I do create the table in the SQLiteOpenHelper class: public class SQLiteHandlerDeliveryItem extends SQLiteOpenHelper { . . . @Override public void onCreate(SQLiteDatabase sqLiteDatabase) { String CREATE_DELIVERYITEMS_TABLE = "CREATE TABLE " + TABLE_DELIVERYITEMS + "(" + COLUMN_ID + " INTEGER PRIMARY KEY," + COLUMN

Why is my constructor not getting called?

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Are class constructors void by default?

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问题 I have been reading on class constructors in C#. Examples are showing overloaded class contructors. And all of them do not have a void keyword and neither they have a return value.. e.g. public Class myClass { public myClass() { } public myClass(int id) { } //other class memeber go here... } 1) So is it correct to say C# constructors are void by default? 2) Does the same applies to Java as well? 回答1: no, they are constructors, if anything, you can think of them as returning an object of the

Class constructor not called when class registration is done in that class constructor

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问题 I am writing a simple dependency injection / inversion of control system based on a TDictionary holding abstract class references with their respective implementor classes. My goals are: Avoid direct instantiation by type (obviously). Inclusion of a class' unit in the dpr should be enough to have it registered and be available for selection and instantiation through the di/ioc system. Declare concrete implementing classes in implementation section only. Use class constructors instead of

Class constructor not called when class registration is done in that class constructor

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I am writing a simple dependency injection / inversion of control system based on a TDictionary holding abstract class references with their respective implementor classes. My goals are: Avoid direct instantiation by type (obviously). Inclusion of a class' unit in the dpr should be enough to have it registered and be available for selection and instantiation through the di/ioc system. Declare concrete implementing classes in implementation section only. Use class constructors instead of initialization sections. Btw, I am aware that using class constructors to take advantage of smart linking

Are class constructors void by default?

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I have been reading on class constructors in C#. Examples are showing overloaded class contructors. And all of them do not have a void keyword and neither they have a return value.. e.g. public Class myClass { public myClass() { } public myClass(int id) { } //other class memeber go here... } 1) So is it correct to say C# constructors are void by default? 2) Does the same applies to Java as well? no, they are constructors, if anything, you can think of them as returning an object of the class they are from. But, they aren't normal method/functions No Constructors implicitly return class type

Can I use C++ class members initialized in the initializer list, later in the list?

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问题 I am rewriting some code to eliminate global variables and made a class constructor/destructor handle cleanup of some third party library resources, but I am concerned about some code which initializes one member from another member in the class initializer list. class MyPodofoDocument { public: // generates pdf to stream MyPodofoDocument(std::stringstream *pStringStream) : device(pStringStream), document(&device) { } private: PoDoFo::PdfOutputDevice device; PoDoFo::PdfStreamedDocument

C++ constructor definition differences in the code given below [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 2 years ago . I am newbie to C++. Learning constructors. Please refer to two codes mentioned below, and provide reason, why Code 2 is not working. Thanks. Code 1: #include <iostream> using namespace std; class Box { int x; public: Box::Box(int a=0) { x = a; } void print(); }; void Box::print() { cout << "x=" << x << endl; }

C++ constructor definition differences in the code given below [closed]

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I am newbie to C++. Learning constructors. Please refer to two codes mentioned below, and provide reason, why Code 2 is not working. Thanks. Code 1: #include <iostream> using namespace std; class Box { int x; public: Box::Box(int a=0) { x = a; } void print(); }; void Box::print() { cout << "x=" << x << endl; } int main() { Box x(100); x.print(); } Code 2: #include <iostream> using namespace std; class Box { int x; public: Box(int a=0); void print(); }; Box::Box(int a=0) { x = a; } void Box::print() { cout << "x=" << x << endl; } int main() { Box x(100); x.print(); } Why the code 1 is working