CSE 1341 Honors

1. CSE 1341 Honors Professor Mark Fontenot Southern Methodist University Note Set 17

2. Software Reuse • DO NOT reinvent the wheel! • If you have source code that works and has been tested, Re-use it! • Simple Example: • Methods • Performs a task • Can accept input to “change” the way the method executes (parameters or overloading).

3. Object Composition • One object contains instances of other objects as data members Car Motor A/C System Braking System

4. Object Composition public class Car { private Motor mSys; private ACSystemacSys; private BrakingSystem brakes; public Car () { mSys = new Motor(); acSys = new ACSystem(); brakes = new BrakingSystem(); } public void start() { mSys.crank(); acSys.previousSettings(); } } Instance Variables can be objects Here is where the contain objects are constructed Car Motor A/C System Braking System Can access various methods from contained objects

5. Inheritance

6. Clock • Scenario – You’ve designed a clock class. You’ve tested it and it works well. Clock • hours : int • minutes: int • seconds: int +setTime(h:int, m:int, s:int) +getTime() : String

7. Alarm Clock • Now you need an alarm clock. Its similar to a clock but needs to also store an alarm time. • You could start again from scratch But that would be silly… AlarmClock • hours : int • minutes: int • seconds: int • alHour : int • alMin : int • alSec : int +setTime(h:int, m:int, s:int) +setAlarmTime(h:int, m:int, s:int) +getTime() : String +getAlarmTime() : String

8. Alarm Clock is a Clock Clock Superclass • Can implement AlarmClockso that it inheritsall of the data and functionality from from Clock • An object of type AlarmClockaugments the functionality of Clock. • hours : int • minutes: int • seconds: int +setTime(h:int, m:int, s:int) +getTime() : String AlarmClock Subclass • alHour : int • alMin : int • alSec : int +setAlarmTime(h:int, m:int, s:int) +getAlarmTime() : String

9. Alarm Clock is a Clock Clock public class Clock { private int hours; private int minutes; private int seconds; //implementation of instance //methods for Clock here } public class AlarmClockextends Clock { private intalHour; private intalMin; private intalSec; //instance methods for AlarmClock //Here } • hours : int • minutes: int • seconds: int +setTime(h:int, m:int, s:int) +getTime() : String AlarmClock • alHour : int • alMin : int • alSec : int indicates that AlarmClock is inheriting from Clock. +setAlarmTime(h:int, m:int, s:int) +getAlarmTime() : String

10. Subclass and Superclasses • Subclass can override the functionality of a method in a superclass • subclass provides a new implementation of the function • must have exactly the same function signature • can call the superclass version of the method by using super.methodName(…);

11. Example: Employee public class Employee { private String id; private double baseSalary; public Employee () { id = "00000000"; baseSalary = 0.00; } public void setID(String temp) { id = temp; } public void setBaseSalary(doubled) { baseSalary = d; } public String getId() { return id; } public double calcMonthlySalary () { return baseSalary / 12; } }

12. Example: BasePlusCommission public class BasePlusCommission extends Employee { private double commissionAmt; public void setCommissionAmt (double d) { commissionAmt = d; } public double calcMonthlySalary () { double temp = super.calcMonthlySalary (); temp += commissionAmt / 12; return temp; } } calls the superclass version of the same method Overrides the functionality of same method from base class