What is a constructor?
snitfaq - Snit's Not Incr Tcl, OO systemIn object-oriented programming, an object's constructor is responsible for initializing the object completely at creation time. The constructor receives the list of options passed to the snit::type command's create method and can then do whatever it likes. That might include computing instance variable values, reading data from files, creating other objects, updating type and instance variables, and so forth.
Related QuestionsHow do I call the constructor?
FAQThe Polynomial(int d, double *coefs) constructor is invoked when an object of type Polynomial is defined using the appropriate arguments. For example, double co[] = { 1.2, 3.4, 5.6 }; Polynomial p(2, co); constructs p to represent 5.6x2 + 3.4 x + 1.2.
Related QuestionsFAQ for the microsoft.public.languages.csharp newsgroupYou use : base (parameters) or : this (parameters) just before the actual code for the constructor, depending on whether you want to call a constructor in the base class or in this class. For more information about constructor chaining, see my article on constructors.Related Questions
Code Style: Java objects frequently asked questions (FAQ)Use the form below to submit a help request or general enquiry about the Code Style Web site. Before you write read the guidelines on asking the right questions, and check this page for periodic updates. Your email address will not be mis-used. If you include your address you may be sent a personal reply, you will not be added to any mailing list unless you request it. Read the site privacy statement for details.Related Questions
What is a type constructor?
snitfaq - Snit's Not Incr Tcl, OO systemA type constructor is a body of code that initializes the type as a whole, rather like a C++ static initializer. The body of a type constructor is executed once when the type is defined, and never again.
Related QuestionsHow do I define a constructor?
snitfaq - Snit's Not Incr Tcl, OO systemA constructor is defined by using the constructor statement in the type definition. Suppose that it's desired to keep a list of all pedigreed dogs. The list can be maintained in a type variable and retrieved by a type method. Whenever a dog is created, it can add itself to the list--provided that it's registered with the American Kennel Club.
Related QuestionsCan constructor be overridden?
JavaChina, SCJP Questions and Answers by Roseanne Zhang (2)Can you explain the result of the following example? Oh, my! class Base { public boolean foo(Base b) { return true; } } class Sub extends Base { public boolean foo(Sub s) { return false; } } public class Test { public static void main(String argv[]) { Base bb = new Base(); Base bs = new Sub(); Sub ss = new Sub(); System.out.println(bb.foo(bb)); //true System.out.println(bs.foo(bs)); //true ??? System.out.println(bs.foo(ss)); //true ??? System.out.println(bs.foo(bb)); //true ??? System.out.
Related QuestionsCan I call a virtual method from a constructor/destructor?
Andy Mc's C# FAQ for C++ programmersYes, but it's generally not a good idea. The mechanics of object construction in .NET are quite different from C++, and this affects virtual method calls in constructors. C++ constructs objects from base to derived, so when the base constructor is executing the object is effectively a base object, and virtual method calls are routed to the base class implementation. By contrast, in .
Related QuestionsWhy won't my servlet compile? Q: Can I use a constructor in my servlet?
Code Style: Java servlets frequently asked questions (FAQ)A servlet is a normal Java class, so when there are no custom constructors, there is an implicit default constructor with no arguments. Servlet containers typically use the Class.newInstance() method to load servlets, so you must be careful to add an explicit default constructor if you add non-default constructors.
Related QuestionsHow do I invoke a constructor? Q: How can I call a constructor from a constructor?
Code Style: Java objects frequently asked questions (FAQ)When you have a number of constructors in a class you can call them using this() in a similar way to the superclass constructor super(). For instance, if you have a "good citizen" constructor that takes a String and a boolean, and a shorthand version that only takes a String, you may pass a default value to the two argument constructor, like so:
Related QuestionsCan I use a constructor in my servlet? Q: Can I use a normal class to handle my requests?
Code Style: Java servlets frequently asked questions (FAQ)Servlets are normal Java classes, they compile and run just like any other class. All that is required is that servlets implement the javax.servlet.Servlet interface. Usually, they extend a protocol-specific class such as javax.servlet.http.HttpServlet.
Related QuestionsWhy copy constructor can only pass-by-reference?
FAQ on C/C++/Unix by Roseanne Zhang, Java Programmer Certifi...That means we will have infinite recursion, until our program is dead!!! Now, our compiler is smart enough to not allow it. If you compile this code, you will get a lot of error message! class A{ public: int i; A(A a){ i = a.i; } } //2 note: candidates are: A::A(const A&) abc.cpp
Related QuestionsHow can I specify the constructor of a class?
docs/compiler_faq.podJust override the init vtable for that class. newclass $P0, 'Dog' # create a class named Dog # ... .namespace ['Dog'] .sub init :vtable # ... Or you can specify the constructor method by setting the BUILD property of the class PMC: newclass $P0, 'Dog' # create a class named Dog new $P1, 'String' # create a string set $P1, 'initialise' # set it to the name of the constructor method setprop $P0, 'BUILD', $P1 # set the BUILD property
Related QuestionsHow can I pass arguments to a constructor?
docs/compiler_faq.podYou can pass only a single argument to a constructor. By convention, a hash PMC is passed to the constructor that contains the arguments as key/value pairs: new $P0, 'Hash' set $P0['greeting'], 'hello' set $P0['size'], 1.23 find_type $I0, 'Alien' new $P1, $I0, $P0 # create an Alien object and pass # the hash to the constructor
Related QuestionsHow do I define a type constructor?
snitfaq - Snit's Not Incr Tcl, OO systemA type constructor is defined by using the typeconstructor statement in the type definition. For example, suppose the type uses an array-valued type variable as a look-up table, and the values in the array have to be computed at start-up. snit::type mytype { typevariable lookupTable typeconstructor { array set lookupTable {key value...} } }
Related QuestionsWhat does the default constructor do?
snitfaq - Snit's Not Incr Tcl, OO systemIf you don't provide a constructor explicitly, you get the default constructor, which is identical to the explicitly-defined constructor shown here: When the constructor is called, args will be set to the list of arguments that follow the object's name. The constructor is allowed to interpret this list any way it chooses; the normal convention is to assume that it's a list of option names and values, as shown in the example above.
Related QuestionsAre there any limitations on constructor arguments?
snitfaq - Snit's Not Incr Tcl, OO systemConstructor argument lists are subject to the same limitations as those on instance method argument lists. It has the same implicit arguments, and can contain default values and the args argument.
Related QuestionsIs there anything special about writing the constructor?
snitfaq - Snit's Not Incr Tcl, OO systemYes. Writing the constructor can be tricky if you're delegating options to components, and there are specific issues relating to snit::widgets and snit::widgetadaptors. See DELEGATION, WIDGETS, WIDGET ADAPTORS, and THE TK OPTION DATABASE.
Related QuestionsHow is a constructor being rated or evaluated?
Tradeline News & Market DevelopmentsWith CPES, the performance of a constructor is evaluated during construction on the aspects of workmanship, materials, time, environmental, safety and health concern, resources deployment, and facilities. However, upon completion the aspects of workmanship and time shall be evaluated. The constructor shall receive a CPES rating from the agency concerned which implements the projects. The rating states both the numerical and descriptive performance of the constructor for each project visit.
Related QuestionsHow and when can the suspension of a blacklisted constructor be lifted?
Tradeline News & Market DevelopmentsThe suspension of a blacklisted constructor may be lifted either automatically or through the issuance of a Delisting Order of the agency concerned depending on the condition of the Blacklisting Order.
Related QuestionsShould you use the this pointer in the constructor?
Constructors, C++ FAQ LiteSome people feel you should not use the this pointer in a constructor because the object is not fully formed yet. However you can use this in the constructor (in the {body} and even in the initialization list) if you are careful. Here is something that always works: the {body} of a constructor (or a function called from the constructor) can reliably access the data members declared in a base class and/or the data members declared in the constructor's own class.
Related QuestionsWhat is the "Named Constructor Idiom"?
Constructors, C++ FAQ LiteA technique that provides more intuitive and/or safer construction operations for users of your class. The problem is that constructors always have the same name as the class. Therefore the only way to differentiate between the various constructors of a class is by the parameter list. But if there are lots of constructors, the differences between them become somewhat subtle and error prone.
Related QuestionsHow can I handle a constructor that fails?
Exceptions and error handling Updated! , C++ FAQ LiteConstructors don't have a return type, so it's not possible to use return codes. The best way to signal constructor failure is therefore to throw an exception. If you don't have the option of using exceptions, the "least bad" work-around is to put the object into a "zombie" state by setting an internal status bit so the object acts sort of like it's dead even though it is technically still alive. The idea of a "zombie" object has a lot of down-side.
Related QuestionsConstructor or not constructor? Please explain why the output of the following code is null?
JavaChina, SCJP Questions & Answers by Roseanne Zhang (3...public class My { String s; public void My(){ s = "Constructor"; } public void go() { System.out.println(s); } public static void main(String args[]) { My m = new My(); m.go(); } } //output : null public void My() is not a constructor. The default constructor is called. s is still null by default.Constructor is not supposed to have a return type, even a void type. If it has, then it is not a constructor, but a method, which happens to have the same name as the class name.
Related QuestionsCan I throw an exception from a constructor? From a destructor?
Stroustrup: C++ Style and Technique FAQYes: You should throw an exception from a constructor whenever you cannot properly initialize (construct) an object. There is no really satisfactory alternative to exiting a constructor by a throw. Not really: You can throw an exception in a destructor, but that exception must not leave the destructor; if a destructor exits by a throw, all kinds of bad things are likely to happen because the basic rules of the standard library and the language itself will be violated. Don't do it.
Related QuestionsWho is the constructor of a Formula One car?
F1A&G - FAQBy Formula One constructor, we mean the chassis manufacturer. In most cases, this is not the same as the engine manufacturer, and the name of the chassis manufacturer is always given before that of the engine manufacturer. In the event of winning the Constructors' World Championship, the title is awarded to the chassis manufacturer.
Related QuestionsCan I call the constructor of the base class?
Frequently asked question about the Scriptol interpreter and...I inherit the class Car of the class Vehicle, for example. Can I call the constructor of Vehicle, from the constructor of Car? I do that in Java. Java has the "super" keyword to call the constructor of a class from the constructor of an inherited class. There is no equivalent in Scriptol. If you call the constructor of the base class, this create a new instance of the base class. But you can assign the attributes of the base class from the constructor of the inherited class.
Related Questionsg++ seems to want a const constructor. What's that?
Frequently asked questions about the GNU C++ compilergcc-2.7.1 introduced a bug that causes the compiler to ask for a const constructor (there's no such thing in C++) in certain situations where a const object appears in a template class. Most cases have been fixed in gcc-2.7.2, but unfortunately not all. Still, if you're running gcc-2.7.1 and have this problem, upgrade to 2.7.2; it is a vast improvement. The default constructor for the template pair in ObjectSpace's implementation of STL triggers the bug in one place, for gcc 2.7.2.
Related QuestionsWhy do I not create a constructor for an applet?
jGuru: Applets FAQAuthor: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) One doesn't see constructors in applets because the applet container doesn't guarantee a complete environment (valid applet context) until the init() method is called.
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