Object interaction Creating cooperating objects 3 0 A

Object interaction Creating cooperating objects 3. 0

A digital clock Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 2

Abstraction and modularization • Abstraction is the ability to ignore details of parts to focus attention on a higher level of a problem. • Modularization is the process of dividing a whole into well-defined parts, which can be built and examined separately, and which interact in well-defined ways. Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 3

Modularizing the clock display One four-digit display? Or two-digit displays? Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 4

Implementation Number. Display public class Number. Display { private int limit; private int value; Constructor and methods omitted. } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 5

Implementation Clock. Display public class Clock. Display { private Number. Display hours; private Number. Display minutes; Constructor and methods omitted. } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 6

Object diagram Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 7

Class diagram Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 8

Primitive types vs. object types Some. Object obj; object type int i; 32 primitive type Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 9

Primitive types vs. object types Object. Type a; Object. Type b; b = a; int a; int b; 32 32 Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 10

Source code: Number. Display public Number. Display(int roll. Over. Limit) { limit = roll. Over. Limit; value = 0; } public void increment() { value = (value + 1) % limit; } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 11

Source code: Number. Display public String get. Display. Value() { if(value < 10) { return "0" + value; } else { return "" + value; } } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 12

Objects creating objects public class Clock. Display { private Number. Display hours; private Number. Display minutes; private String display. String; public Clock. Display() { hours = new Number. Display(24); minutes = new Number. Display(60); update. Display(); } } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 13

Method calling public void time. Tick() { minutes. increment(); if(minutes. get. Value() == 0) { // it just rolled over! hours. increment(); } update. Display(); } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 14

Internal method /** * Update the internal string that * represents the display. */ private void update. Display() { display. String = hours. get. Display. Value() + ": " + minutes. get. Display. Value(); } Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 15

Clock. Display object diagram Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 16

Objects creating objects in class Number. Display: public Number. Display(int roll. Over. Limit); formal parameter in class Clock. Display: hours = new Number. Display(24); actual parameter Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 17

Method calls • internal method calls update. Display(); . . . private void update. Display() • external method calls minutes. increment(); Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 18

Method calls (2) object. method. Name ( parameter-list ) Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 19

Concepts • abstraction • modularization • classes define types • class diagram • object references primitive types object creation overloading internal/external method call • debugger • • • Objects First with Java - A Practical Introduction using Blue. J, © David J. Barnes, Michael Kölling 20