Constructors are subroutines that are called during the creation of a new class-based object in object-oriented-programming. These sub-routines are responsible for defining the newly-instantiated object with state.<\/p>\n
Constructors may accept arguments, have no return type, and are not implicitly inherited. Constructors initialize an object’s data members with values calculated from arguments, by using defaults, or by other programmer-defined routines.<\/p>\n
Constructors are often abbreviated as ctor, particularly in abstract model representations like UML diagrams.<\/p>\n
Below is an example of a constructor for an Constructors can, in most languages, be overloaded such that multiple combinations of arguments can be used to initialize a new class object on instantiation. This allows programmers to set defaults for cases where inputs may not be necessary. Below is an example of constructor overloading in Java:<\/p>\n In the second example, another constructor form has been added that allows the creation of an Constructor chaining is an approach of programming constructor methods that can be used during inheritance or during constructor overloading. It provides a means for programmers to avoid redundancy in setting class data members and blends seamlessly with overloading.<\/p>\n In the example above, a name field has been added to the class and is hard-coded. The number value can still be set dynamically during the instantiation of a new class object. The other constructor method\u2014the one requiring no arguments\u2014instantiates a new class object by chaining <\/em>with the default constructor. In this context, constructor chaining means calling one constructor method from within another.<\/p>\n The benefit here is that the Chaining Constructor method does not have to bother setting the default value for the name field\u2014it lets the default constructor handle that. This helps avoid having to code this class as follows:<\/p>\n The reduction of redundancy and lines of code isn’t great in this contrived example. However, more complex application design can benefit greatly by using constructor chaining, particularly in cases of inheritance and polymorphism.<\/p>\nExample<\/code> class in Java:<\/p>\npublic class Example {\r\n \r\n \/\/ Data members\r\n private int number;\r\n \r\n \/\/ Constructor\r\n public Example(int number){\r\n this.number = number;\r\n }\r\n \r\n}<\/pre>\nConstructor Overloading<\/h2>\n
public class Example {\r\n\r\n \/\/ Data members\r\n private int number;\r\n\r\n \/\/ Constructor with argument\r\n public Example(int number){\r\n this.number = number;\r\n }\r\n\r\n \/\/ Constructor without argument\r\n public Example(){\r\n this.number = 1234;\r\n }\r\n\r\n}<\/pre>\nExample<\/code> class object without providing an argument for number<\/code>. In this example, the code specifies a default value of 1234<\/code> that will be set to the newly-created class object’s number<\/code> field.<\/p>\nConstructor Chaining<\/h2>\n
public class Example {\r\n\r\n \/\/ Data members\r\n private int number;\r\n private String name;\r\n\r\n \/\/ Default Constructor\r\n public Example(int number){\r\n this.number = number;\r\n this.name = \"Example\";\r\n }\r\n\r\n \/\/ Chaining Constructor\r\n public Example(){\r\n this(1234);\r\n }\r\n}<\/pre>\npublic class Example {\r\n\r\n \/\/ Data members\r\n private int number;\r\n private String name;\r\n\r\n \/\/ Constructor\r\n public Example(int number){\r\n this.number = number;\r\n this.name = \"Example\";\r\n }\r\n\r\n \/\/ Constructor without argument\r\n public Example(){\r\n this.number = 1234;\r\n this.name = \"Example\"; \/\/ redundant\r\n }\r\n\r\n}<\/pre>\nDefault Constructors<\/h2>\n