Object-Oriented Data-Structures - A Concise and Practical Introduction to Programming Algorithms in Java - page 181

function: an object method. The object field is accessed using the reserved
keyword this .

Program 8.9 Object methods for the list

class ListObj
int container ;
ListObj next ;

ListObj( int element , ListObj tail )

{ this .container=element;

this .next=tail; }

ListObj insert ( int s)
{ return new ListObj(s , this ); }

// Method
int head ()
{ return this .container; }
}

In the main procedure, we could have then used the following instructions:
ListObj list= new ListObj (7 , null );
list=list . insert(4);
System . out . println ( "Head:" +list .head());

In the remainder, we will adopt this object-oriented framework when designing
data-structures, as they correspond to a true data encapsulation. 4 We will first
present the (class) static function and then describe the corresponding object-
oriented data-structure.
As concisely mentioned in the introduction, we made a difference between data-
structures with static functions operating on them, and encapsulated methods
acting directly on the object itself. We shall further describe these concepts
of object-oriented programming and revisit former data-structures using that
framework (replacing static functions by equivalent object methods).
To start with, consider the following example where one has to compute
the volume of a 3D box. First, we define a Box object by writing its class
encapsulating its data members: width , height ,and depth . So far, the usual
way to process a Box has been using static functions that were necessarily
attached to a class. So let us define the static double Volume(Box box)
function inside the body of the main class program. Note that this static
function needs a Box object as argument. The second (and much better way) to
program this functionality is to provide a method to the object that will dispose
of all the object fields at the time it is called. We access the various object fields

4 A second more advanced course will then purposely describe the public / private
keyword syntax.