Even even more on being classy

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Even even more on being classy

• Aaron Bloomfield
• CS 101-E
• Chapter 4

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Consider this sequence of events
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What happened?

• Java didnt 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!

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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()

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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

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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

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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.set
Size(200, 200) window.setVisible(true) //
paint() display the rectangle in its
window public void paint() Graphics g
window.getGraphics() g.setColor(color) g.fil
lRect(x, y, width, height)
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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
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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

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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()

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Vector code example

• 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)

0 1 first 3 first, second,
third third (Exception) 2 first,
third 0
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What we wish computers could do
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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

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About that exception

• The exact exception was
• Exception in thread "main" java.lang.ArrayIndexOut
  OfBoundsException 3 gt 3
• at java.util.Vector.elementAt(Vector.java
  431)
• at VectorTest.main(VectorTest.java15)

Where the problem occured
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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.java7
  cannot resolve symbol
• symbol method add (int)
• location class java.util.Vector
• v.add (1)

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What happened?

• The Vector add() method
• boolean add(Object o)
• Primitive types are not objects!
• Solution use wrapper classes!

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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 dont have the exact same
  name as their wrapper classes

• Integer
• Long
• Float
• Double

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Vector code example

• 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)

0 1 1 3 1, 2, 3 3 (Exception)
2 1, 3 0
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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)

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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)

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An optical illusion
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Design an air conditioner representation

• Context
• Repair person
• Sales person
• Consumer
• Behaviors
• Attributes

- Consumer
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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

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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

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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

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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

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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

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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

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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

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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

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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

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Ugh
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Design an air conditioner representation

• // Represent an air conditioner from consumer
  view point
• public class AirConditioner
• // instance variables
• // constructors
• // methods
• Source AirConditioner.java

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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

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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

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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

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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

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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

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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

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Facilitator toString()

• // toString() produce a String representation of
  the object
• public String toString()
• String result " power " this.powerSetting
  
• ", fan " this.fanSetting
• ", temperature " this.temperatureSettin
  g
• " "
• return result

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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

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What computers were made for

• NASAs WorldWind
• See http//learn.arc.nasa.gov/worldwind/