Programming with Objects

Object Interaction (Part 1)

Week 9

• Abstraction & modularisation

• The modulo operator

Programming with Objects CONCEPTS COVERED THIS WEEK

• Abstraction is the ability to ignore details of parts to focus attention on a higher level of a problem.

• Modularisation is the process of dividing a whole into a set of well-defined parts, where each part can be built and tested separately, and where each part only interacts with other parts in well-defined ways.

Programming with ObjectsABSTRACTION & MODULARISATION

It is an object that is made up of other objects!

Wheels, Seats, Chassis, Exhaust, Steering Wheel, etc.

This car is a Complex Object

And… a wheel itself is also a complex object!

Tyre, Trim, Hub Cap, etc.

ABSTRACTION

Object Model

MODULARISATION

Object Model

Team 1 works on producing the Engine Design:

Team 2 works on producing the Seat Design:

Team 3 works on producing the Wheel Design:

Team 3a works on producing the

Tyre Design:

Programming with Objects ABSTRACTION & MODULARISATION

A digital clock

Programming with Objects ABSTRACTION & MODULARISATION

Modularising the clock display

One four-digit display?

Or two two-digit displays?

BlueJ DemonstrationA look at the NumberDisplay class

Programming with Objects Source Code - NumberDisplay

public class NumberDisplay{ private int limit; private int value;

// Constructor and methods // omitted.}

Programming with Objects Source Code - NumberDisplay

public NumberDisplay(int rollOverLimit){ limit = rollOverLimit; value = 0;}

public int getValue(){ return value;}

Programming with Objects Source Code - NumberDisplay

public String getDisplayValue(){ if(value < 10) { return "0" + value; } else { return "" + value; }}

Programming with Objects Source Code - NumberDisplay

public void setValue(int replacementValue){ if((replacementValue >= 0) && (replacementValue < limit)) { value = replacementValue; }}

Modulo (or modulus or mod) operator

• The % operator gives the remainder of a division

• result = 10 % 3;

• assigns a value of 1 to result

• result = 15 % 6;

• result = 19 % 11;

Programming with Objects Source Code - NumberDisplay

public void increment(){ value = (value + 1) % limit;}

Required ReadingObjects First With Java – A Practical Introduction using

BlueJ

Related reading for this lecture• Chapter 3