CSC/ECE 517 Fall 2011/ch1 1h ps

Common Attribute/Member Syntax

Different object oriented programming languages include different ways of accessing the member variables and methods. This page discusses the various usages and their advantages and disadvantages.

Introduction

The purpose of Object Oriented Programming is to make programs model things the way people think or deal with the world i.e it's modeled around data rather than logic. Objects form the basis of OOP. Let us now look at objects, their manipulation and the ways to do so.

Objects - Attributes and Methods

Similar to real world objects, software objects also consist of state and related behavior. An object stores it's state in attributes and exposes its behavior through methods. Let's look at the pseudo code for a bicycle object. CLASS Bicycle ATTRIBUTES: speed: NUMBER gear: NUMBER pedal_cadence: NUMBER METHODS: ride(speed) changeGear(gear) changeCadence(pedal_cadence)

In the above pseudo code, the attributes define the object and the methods provide a way of achieving the desired functionality from that object. The methods use the attributes to manipulate the object and achieve the functionality. From this we can observe that this manipulation is the very essence of programming using objects. Therefore the access of attributes and way of defining method calls very important in OOP.

Method call / Instance Variable reference Syntax

A running debate in O-O languages is whether method calls and instance-variable references should have the same syntax. Different programming languages implement this in different ways. Let's look at them by examples.

Same Syntax

Languages like Ruby use the same syntax for method calls and variable references. There is no distinction between these. We can see this in the example below:

class Song
  def duration=(newDuration)
    @duration = newDuration
  end
end
aSong = Song.new("Bicylops", "Fleck", 260)
aSong.duration	»	260
aSong.duration = 257   # set attribute with updated value
aSong.duration	»	257

This makes it simpler for the programmer to code. Also, it presents uniformity in the code.

Differing Syntax

Languages like Java employ different syntax for method calls and variable references as seen in this example below:

class Song{
	int duration;
	Song(){}
	void setDuration(int dur){
		duration = dur;
	}
}

Song sng = new Song();
sng.setDuration(260);
System.out.println("Song duration = "+sng.duration);

As seen above, a method is always called using parenthesis, within which arguments may be included if required. However, instance variable is accessed directly.

Comparison of syntax between various Programming Languages

The usage syntax of methods, instance variables, getters and setters is in the table below

Programming Languages	Method call	Fields/Attributes	Getter / Setter	Comparison
ABAP (Advanced Business Application Programming)	CALL METHOD <meth> EXPORTING... <ii> =.<f i>... IMPORTING... <ei> =.<g i>... CHANGING ... <ci> =.<f i>... RECEIVING r = h EXCEPTIONS... <ei> = rc i...	data field type type	Same as other methods with the only difference that they start with SET or GET	Syntax is different for method calls and instance-variable reference