Constructor

Techopedia explains Constructor

Constructors are not called explicitly and are invoked only once during their lifetime. In the case of a hierarchy of classes where a derived class inherits from a parent class, the execution sequence of the constructor is a call to the constructor of the parent class first and then that of the derived class. Constructors cannot be inherited.

A constructor can be declared using any of the access modifiers. It is mandatory to have a constructor with the right access modifier. However, the compiler supplies a default if an access modifier is not defined in the class. If a constructor is declared as private, the class cannot be created or derived and hence cannot be instantiated. Such a constructor, however, can be overloaded with different sets of parameters.

The following is recommended in constructor design:

• Logic involving specific operations that need to be executed at a particular event in an application - such as opening a database connection - should not be written in a constructor.

• When using derived class constructors, the parent class constructor should be passed the correct parameters.

• Better code maintainability comes from having the initialization and other related logic in one main constructor and cross-calling this constructor from other overloaded constructors.

• Because a constructor cannot return a value to the calling code, it is a good practice to throw an exception when a failure is encountered.