Even even more on being classy

1. Even even more on being classy Aaron Bloomfield CS 101-E Chapter 4+

2. Consider this sequence of events…

3. What happened? • Java didn’t “repaint” the rectangles when necessary • Java only painted the rectangle once • You can tell Java to repaint it whenever necessary • This is beyond the scope of this class, though!

4. Seeing double import java.awt.*; public class SeeingDouble { public static void main(String[] args) { ColoredRectangle r = new ColoredRectangle(); System.out.println("Enter when ready"); Scanner stdin = new Scanner (System.in); stdin.nextLine(); r.paint(); r.setY(50); r.setColor(Color.RED); r.paint(); } }

5. Seeing double • When paint() was called, the previous rectangle was not erased • This is a simpler way of implementing this • Perhaps clear and repaint everything when a rectangle paint() is called

6. Code from last class // Purpose: Create two windows containing colored rectangles. import java.util.*; public class BoxFun { //main(): application entry point public static void main (String[] args) { ColoredRectangle r1 = new ColoredRectangle(); ColoredRectangle r2 = new ColoredRectangle(); System.out.println("Enter when ready"); Scanner stdin = new Scanner (System.in); stdin.nextLine(); r1.paint(); // draw the window associated with r1 r2.paint(); // draw the window associated with r2 } }

7. public class ColoredRectangle { // instance variables for holding object attributes private int width; private int x; private int height; private int y; private JFrame window; private Color color; // ColoredRectangle(): default constructor public ColoredRectangle() { color = Color.BLUE; width = 40; x = 80; height = 20; y = 90; window = new JFrame("Box Fun"); window.setSize(200, 200); window.setVisible(true); } // paint(): display the rectangle in its window public void paint() { Graphics g = window.getGraphics(); g.setColor(color); g.fillRect(x, y, width, height); } }

8. ColorRectangle ColorRectangle - width = 40 - width = 0 - height = 0 - height = 20 - x = 0 - x = 80 - y = 90 - y = 0 - color = - color = - window = - window = + paint() : void + paint() : void JFrame - width = 200 - height = 200 Color - title = String - color = - grafix = Graphics - ... - ... - text = “Box Fun” - … - ... + brighter() : Color + setVisible (boolean status) : void + getGraphics () : Graphics + setSize (int w, int h) : void + … + fillRect() : void + ... + length() : int + setColor(Color) : void + ... + ... ColoredRectangle r = new ColoredRectangle(); r public class ColoredRectangle { private int width; private int x, y; private int height; private int y; private JFrame window; private Color color; public void paint() { Graphics g = window.getGraphics(); g.setColor(color); g.fillRect (x, y, width, height); } public ColoredRectangle() { color = Color.BLUE; width = 40; height = 20; y = 90; x = 80; window = new JFrame ("Box Fun"); window.setSize (200, 200); window.setVisible (true); } g

9. The Vector class • In java.util • Must put “import java.util.*;” in the java file • Probably the most useful class in the library (in my opinion) • A Vector is a collection of “things” (objects) • It has nothing to do with the geometric vector

10. Vector methods • Constructor: Vector() • Adding objects: add (Object o); • Removing objects: remove (int which) • Number of elements: size() • Element access: elementAt() • Removing all elements: clear()

11. Vector code example 0 [] 1 [first] 3 [first, second, third] third (Exception) 2 [first, third] 0 [] Vector v = new Vector(); System.out.println (v.size() + " " + v); v.add ("first"); System.out.println (v.size() + " " + v); v.add ("second"); v.add ("third"); System.out.println (v.size() + " " + v); String s = (String) v.elementAt (2); System.out.println (s); String t = (String) v.elementAt (3); System.out.println (t); v.remove (1); System.out.println (v.size() + " " + v); v.clear(); System.out.println (v.size() + " " + v);

12. What we wish computers could do

13. The usefulness of Vectors • You can any object to a Vector • Strings, ColoredRectanges, JFrames, etc. • They are not the most efficient for some tasks • Searching, in particular

14. About that exception… • The exact exception was: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3 >= 3 at java.util.Vector.elementAt(Vector.java:431) at VectorTest.main(VectorTest.java:15) Where the problem occured

15. A Vector of ints • Consider the following code: Vector v = new Vector(); v.add (1); • Causes a compile-time error • Most of the time - see disclaimer later C:\Documents and Settings\Aaron\My Documents\JCreator\VectorTest\VectorTest.java:7: cannot resolve symbol symbol : method add (int) location: class java.util.Vector v.add (1);

16. What happened? • The Vector add() method: • boolean add(Object o) • Primitive types are not objects! • Solution: use wrapper classes!

17. More on wrapper classes • A wrapper class allows a primitive type to act as an object • Each primitive type has a wrapper class: • Boolean • Character • Byte • Short • Note that char and int don’t have the exact same name as their wrapper classes • Integer • Long • Float • Double

18. Vector code example 0 [] 1 [1] 3 [1, 2, 3] 3 (Exception) 2 [1, 3] 0 [] Vector v = new Vector(); System.out.println (v.size() + " " + v); v.add (new Integer(1)); System.out.println (v.size() + " " + v); v.add (new Integer(2)); v.add (new Integer(3)); System.out.println (v.size() + " " + v); Integer s = (Integer) v.elementAt (2); System.out.println (s); Integer t = (Integer) v.elementAt (3); System.out.println (t); v.remove (1); System.out.println (v.size() + " " + v); v.clear(); System.out.println (v.size() + " " + v);

19. Even more on wrapper classes • They have useful class (i.e. static) variables: • Integer.MAX_VALUE • Double.MIN_VALUE • They have useful methods: • String s = “3.14159”; • double d = Double.parseDouble (s);

20. A disclaimer • Java 1.5 (which we are not using) has a new feature called “autoboxing/unboxing” • This will automatically convert primitive types to their wrapper classes (and back)

21. An optical illusion

22. Design an air conditioner representation • Context • Repair person • Sales person • Consumer • Behaviors • Attributes - Consumer

23. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting • Build – construction • Debug • Attributes

24. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting • Build – construction • Debug – to stringing • Attributes

25. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting – mutation • Build – construction • Debug – to stringing • Attributes

26. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting – accessing • Set temperature and fan setting – mutation • Build – construction • Debug – to stringing • Attributes

27. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on – mutation • Turn off – mutation • Get temperature and fan setting – accessing • Set temperature and fan setting – mutation • Build – construction • Debug – to stringing • Attributes

28. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on – mutation • Turn off – mutation • Get temperature and fan setting – accessing • Set temperature and fan setting – mutation • Build – construction • Debug – to stringing • Attributes

29. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting • Build -- construction • Debug • Attributes • Power setting • Fan setting • Temperature setting

30. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting • Build -- construction • Debug • Attributes • Power setting • Fan setting • Temperature setting – integer

31. Design an air conditioner representation • Context - Consumer • Behaviors • Turn on • Turn off • Get temperature and fan setting • Set temperature and fan setting • Build -- construction • Debug • Attributes • Power setting – binary • Fan setting – binary • Temperature setting – integer

32. Ugh…

33. Design an air conditioner representation // Represent an air conditioner – from consumer view point public class AirConditioner { // instance variables // constructors // methods } • Source AirConditioner.java

34. Static variables and constants // shared resource for all AirConditioner objects static public final int OFF = 0; Static public final int ON = 1; static public final int LOW = 0; Static public final int HIGH = 1; static public final int DEFAULT_TEMP = 72; • Every object in the class has access to the same static variables and constants • A change to a static variable is visible to all of the objects in the class • Examples StaticDemo.java and DemoStatic.java

35. Instance variables // individual object attributes int powerSetting; int fanSetting; int temperatureSetting; • Instance variables are always initialized as soon the object comes into existence • If no value is specified • 0 used for numeric variables • false used for logical variables • null used for object variables • Examples InitializeDemo.java

36. Constructors // AirConditioner(): default constructor public AirConditioner() { this.powerSetting = AirConditioner.OFF; this.fanSetting = AirConditioner.LOW; this.temperatureSetting = AirConditioner.DEFAULT_TEMP; } // AirConditioner(): specific constructor public AirConditioner(int myPower, int myFan, int myTemp) { this.powerSetting = myPower; this.fanSetting = myFan; this.temperatureSetting = myTemp; } • Example AirConditionerConstruction.java

37. Simple mutators // turnOn(): set the power setting to on public void turnOn() { this.powerSetting = AirConditioner.ON; } // turnOff(): set the power setting to off public void turnOff() { this.powerSetting = AirConditioner.OFF; } • Example TurnDemo.java

38. Simple accessors // getPowerStatus(): report the power setting public int getPowerStatus() { return this.powerSetting; } // getFanStatus(): report the fan setting public int getFanStatus() { return this.fanSetting; } // getTemperatureStatus(): report the temperature setting public int getTemperatureStatus () { return this.temperatureSetting; } • Example AirConditionerAccessors.java

39. Parametric mutators // setPower(): set the power setting as indicated public void setPower(int desiredSetting) { this.powerSetting = desiredSetting; } // setFan(): set the fan setting as indicated public void setFan(int desiredSetting) { this.fanSetting = desiredSetting; } // setTemperature(): set the temperature setting as indicated public void setTemperature(int desiredSetting) { this.temperatureSetting = desiredSetting; } • Example AirConditionerSetMutation.java

40. Facilitator toString() // toString(): produce a String representation of the object public String toString() { String result = "[ power: " + this.powerSetting + ", fan: " + this.fanSetting + ", temperature: " + this.temperatureSetting + " ] "; return result; }

41. Sneak peek facilitator toString() public String toString() { String result = "[ power: " ; if ( this.powerSetting == AirConditioner.OFF ) { result = result + "OFF"; } else { result = result + "ON " ; } result = result + ", fan: "; if ( this.fanSetting == AirConditioner.LOW ) { result = result + "LOW "; } else { result = result + "HIGH"; } result = result + ", temperature: " + this.temperatureSetting + " ]"; return result; }

42. What computers were made for • NASA’s WorldWind • See http://learn.arc.nasa.gov/worldwind/