1. Nov 5, Fall 2006IAT 8001 Lecture 5 Objects, Classes

2. Nov 5, Fall 2006IAT 8002 Today  Primitive types –byte, short, int, long  Object-oriented programming –objects –classes sets (mutators) and gets (accessors) object methods

3. Nov 5, Fall 2006IAT 8003 Primitive types  Primitive types are determined by machine architecture byte: 8bitsreference: (JVM Dependent) short:16bits int: 32bits long:64bits float:32bits double:64bits

4. Nov 5, Fall 2006IAT 8004 Reference  Like a remote control  a reference is a primitive thing that points at objects  the new keyword causes the reference to point at a new instance of the object

5. Nov 5, Fall 2006IAT 8005

6. Nov 5, Fall 2006IAT 8006 Arrays  int[] nums = new int[7] ;

7. Nov 5, Fall 2006IAT 8007 Array of objects  Dog[] pets = new Dog[7];  It starts as an array of null references

8. Nov 5, Fall 2006IAT 8008 Array of objects Dog[] pets = new Dog[7] ; pets[0] = new Dog(); pets[1] = new Dog();

9. Nov 5, Fall 2006IAT 8009 Objects

10. Nov 5, Fall 2006IAT 80010 Real Objects  Real-world objects have –State –Behavior  Bicycle –State selected gear, current pedal cadence, speed –Behavior Change Gear, Set Cadence, Apply Brakes

11. Nov 5, Fall 2006IAT 80011 Software Object  State int gear ; float speed ; float cadence ;  Behavior ChangeGears(int g); Brake( float level ); ChangeCadence( float c ); int GetGear(); float GetSpeed(); …

12. Nov 5, Fall 2006IAT 80012 Java directly supports Objects  Java has direct syntactic and semantic support for Objects Syntax: class Bicycle { private int cadence = 0; private int speed = 0; private int gear = 1; void changeCadence(int newValue) { cadence = newValue; } void changeGear(int newValue) { gear = newValue; }

13. Nov 5, Fall 2006IAT 80013 Java directly supports Objects  Java has direct syntactic and semantic support for Objects Semantics: class Bicycle { private int cadence = 0; private int speed = 0; private int gear = 1; void changeCadence(int newValue) { cadence = newValue; } void changeGear(int newValue) { gear = newValue; } Only these methods can read or write Bicycle private data

14. Nov 5, Fall 2006IAT 80014 Java Semantic support  Programming usually takes place with objects: ClockClass clock = new ClockClass(); clock.setSecond( 12 ); clock.setMinute( 18 ); clock.setHour( 3 );

15. Nov 5, Fall 2006IAT 80015 Even Arrays are objects int[] bob = new int[10] ; bob[4] = 123 ; println( bob.size() ); Bicycle[]bikes = new Bicycle[10] ; bikes[0] = new Bicycle();

16. Nov 5, Fall 2006IAT 80016 Sets and Gets  what can you do with private data? –to set it: setVarName( varType newValue) –to get it: varType getVarName()  Why?

17. Nov 5, Fall 2006IAT 80017 temperature object class temp { private floatkelvin ; setCelsius( float C ); { if( C < -273.15 ) return ;// perhaps an error message would be in order else kelvin = C + 273.15 ; } float getCelsius() { return( kelvin - 273.15 ); } float setKelvin( float k ) { if( k < 0 ) return ; else kelvin = k ; }

18. Nov 5, Fall 2006IAT 80018 temperature object  Controls access  Ensures correctness –can only run a setXYZ() to change temp –can only do getXYZ() to get the value in the desired scale  Who cares?

19. Nov 5, Fall 2006IAT 80019 Who cares?  When you want to: –Solve the problem once and forget it –Reuse the solution elsewhere –Establish rules for use and change of data  The principle: –Information hiding –By interacting only with an object's methods, the details of its internal implementation remain hidden from the outside world.

20. Nov 5, Fall 2006IAT 80020 Principle: Code re-use  If an object already exists, you can use that object in your program.  Specialists build, you use

21. Nov 5, Fall 2006IAT 80021 Principle: Define the Interface  Define the interface: –The list of methods with Defined Operation  The interface is the thing that other people use  If you have the same interface with the same meaning –You can plug in a better implementation!

22. Nov 5, Fall 2006IAT 80022 Define the Interface  If you have the same interface with the same meaning –You can plug in a better implementation! –You can plug in a More Interesting implementation!

23. Nov 5, Fall 2006IAT 80023 Summary of principles  Hide unnecessary details  Clearly define the interface  Allow and support code re-use  Build on the work of others

24. Nov 5, Fall 2006IAT 80024 How do we build on other work?  Divide and conquer –Cut the problem into smaller pieces –Solve those smaller problems –Aggregate the smaller solutions  Two approaches: –Top-down –Bottom-up

25. Nov 5, Fall 2006IAT 80025

26. Nov 5, Fall 2006IAT 80026 Top Down  Take the big problem –Cut it into parts Analyze each part –Design a top-level solution that presumes you have a solution to each part  then… –Cut each part into sub-parts

27. Nov 5, Fall 2006IAT 80027 Bottom-up  Cut the problem into parts, then sub- parts, then sub-sub parts… –build a solution to each sub-sub-part aggregate sub-sub solutions into a sub-solution

28. Nov 5, Fall 2006IAT 80028 How do we build on other work?  Recognize the problem as another problem in disguise –It’s a sorting problem! –It’s a search problem! –It’s a translation problem! –It’s an optimization problem!

29. Nov 5, Fall 2006IAT 80029 The challenge  Software design is typically done top- down  Software implementation is typically done bottom-up