Java Reference
In-Depth Information
In Display 4.13, we have used overloading to create five constructors for the class
Date . It is normal to have more than one constructor. Since every constructor must
have the same name as the class, all the constructors in a class must have the same
name. So, when you define multiple constructors, you must use overloading.
Note that when you define a constructor, you do not give any return type for the
constructor; you do not even use void in place of a return type. Also notice that con-
structors are normally public.
All the constructor definitions in Display 4.13 initialize all the instance variables,
even if there is no parameter corresponding to that instance variable. This is normal.
In a constructor definition, you can do pretty much anything that you can do in
any ordinary method definition, but normally you only perform initialization tasks
such as initialization of instance variables.
When you create a new object with the operator new , you must always include the
name of a constructor after the operator new . This is the way you invoke a constructor.
As with any method invocation, you list any arguments in parentheses after the con-
structor name (which is the same as the class name). For example, suppose you want to
use new to create a new object of the class Date defined in Display 4.13. You might do
so as follows:
constructor
arguments
Date birthday = new Date("December", 16, 1770);
This is a call to the constructor for the class Date that takes three arguments: one of
type String and two of type int . This creates a new object to represent the date
December 16, 1770, and sets the variable birthday so that it names this new object.
Another example is the following:
Date newYearsDay = new Date(3000);
This creates a new object to represent the date January 1, 3000, and sets the variable
newYearsDay so that it names this new object.
Constructor
A constructor is a variety of method that is called when an object of the class is created
using new . Constructors are used to initialize objects. A constructor must have the same
name as the class to which it belongs. Arguments for a constructor are given in parentheses
after the class name, as in the following examples.
EXAMPLES
Date birthday = new Date("December", 16, 1770),
theDate = new Date(2008);
A constructor is defined very much like any ordinary method except that it does not have a
type returned and does not even include a void in the constructor heading. See Display
4.13 for examples of constructor definitions.
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