Objects and Strings - A Concise and Practical Introduction to Programming Algorithms in Java - page 110

// Constructor (method)
Date( int day , int month , int year)
this .dd=day;
this .mm=month ;
this . yyyy=year ;
}

}

class DemoDate {
public static void main( String [ ] args )

{ Date day= new Date(23 ,12 ,1971) ;
System . out . println ( "Date:" +day . dd+ "/" +day .mm+ "/" +day . yyyy) ;
}
}

A class may potentially supply several constructors provided that they all bear
different signatures. For now, it is best to define a single constructor that
initializes all the fields of the object. Fields of the current object are accessed
by using the keyword this . Although it is not mandatory to use it explicitly
inside the constructor, we recommend initializing the object records in the
constructor by using this :
Date(int day, int month, int year)
{this.dd=day;
this.mm=month;
yyyy=year; // we omitted the keyword this here
}

Note that in cases where no constructor is provided, Java will use a default
constructor common to all objects. Fields can still be assigned after the object
creation as follows:
Date day=new Date();// default constructor called
day.yyyy=1971;
...

We can visualize the object creation and its relationship as depicted in
Figure 5.1.

5.2.2 The common null object

Similar to arrays, we can first define object variables and create/initialize them
later. For example, consider the following code:
Date day;
...// do some instructions here
Date day=new Date(23,12,1971);