A default constructor initializes an object in object-oriented programming and must have no parameters or assign default values. Subclass constructors should call superclass constructors. Default nullary constructors can reduce the number of methods but make code harder to understand. Access modifiers can be associated with any default constructor.
A default constructor is a specialized method that creates and initializes an object in object-oriented programming. There are multiple types of constructors, but a default constructor must meet one of two specific criteria, as well as create and initialize an object. It must have no parameters, in which case it might as well be called a nullary constructor, or it must assign default values to any parameters it is able to set. Some computer languages implicitly specify a default nullary constructor if the programmer does not specify a constructor at all. Once any type of constructor is written, the default nullary constructor is no longer specified and must be explicitly written if necessary.
For computer languages that allow object-oriented inheritance, the default constructors in subclasses must be linked precisely to constructors in superclasses. Subclass constructors should always call superclass constructors before doing anything subclass-specific. In some languages, such as Java®, a subclass constructor implicitly calls a superclass’s default null constructor. If there is no default nullary constructor of the superclass, the subclass object cannot compile successfully. Subclasses can still have both types of default constructor in this case, but an available superclass constructor must be called properly, perhaps passing it unique default values for the subclass.
The implicit generation of a default nullary constructor has the advantage of reducing the number of methods a programmer has to specify and document, but it also has the disadvantage of making it more difficult to maintain and understand the code. Some programmers consider omitting a default constructor bad practice, while others do not. There’s nothing to stop an individual programmer from adhering to one of these programming methods, so including a default nullary constructor in your code is largely a stylistic choice on the programmer’s part. If the constructor is included, most schools of thought dictate that it must be commented and documented just like any other constructor or method.
Any default constructor can have access modifiers associated with it, making the constructor public, protected, or private. This gives the builder specific abilities based on the class it is specified in. A default public constructor can be used to create a new object from another class, while a protected constructor can only be called by its own class and any subclasses. Safe default constructors often appear in an inheritance hierarchy. Private constructors are usually only employed in self-contained classes, where some kind of factory method is available to call it, rather than the programmer.
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