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In Java, a "default constructor" refer to a nullary constructor that is automatically generated by the compiler if no constructors have been defined for the class or in the absence of any programmer-defined constructors (e.g. in Java, the default constructor implicitly calls the superclass's nullary constructor, then executes an empty body ...
Notably, a constructor is a class method as there is no object (instance) available until the object is created, but destructors, initializers, and finalizers are instance methods. Further, constructors and initializers often can accept arguments, while destructors and finalizers generally do not as they are often implicitly callable.
A constructor is a method that is called at the beginning of an object's lifetime to create and initialize the object, a process called construction (or instantiation). Initialization may include an acquisition of resources. Constructors may have parameters but usually do not return values in most languages. See the following example in Java:
In object-oriented programming, a destructor (sometimes abbreviated dtor [1]) is a method which is invoked mechanically just before the memory of the object is released. [2] It can happen when its lifetime is bound to scope and the execution leaves the scope, when it is embedded in another object whose lifetime ends, or when it was allocated dynamically and is released explicitly.
Also, messages can be sent to network resources using RAII. In this case, the RAII object would send a message to a socket at the end of the constructor, when its initialization is completed. It would also send a message at the beginning of the destructor, when the object is about to be destroyed.
The terminology of finalizer and finalization versus destructor and destruction varies between authors and is sometimes unclear.. In common use, a destructor is a method called deterministically on object destruction, and the archetype is C++ destructors; while a finalizer is called non-deterministically by the garbage collector, and the archetype is Java finalize methods.
There are exceptions for special cases as posed by the default constructor. Also note the virtual destructors in the base classes, B1 and B2. They are necessary to ensure delete d can free up memory not just for D, but also for B1 and B2, if d is a pointer or reference to the types B1 or B2. They were excluded from the memory layouts to keep ...
Languages differ in their behavior while the constructor or destructor of an object is running. For this reason, calling virtual functions in constructors is generally discouraged. In C++, the "base" function is called. Specifically, the most derived function that is not more derived than the current constructor or destructor's class is called.