Parameters, Graphical Output COMP 102

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Parameters, Graphical OutputCOMP 102 6 2008
T2
2
Menu

• Method with parameters
• Simple Graphical Output
• Administrivia
• Next Friday 5 test (only counts if it helps)

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Another Java Program

• / Program for converting between temperature
  scales /
• public class TemperatureConverter
• / Print out the conversion formula /
• public void printFormula()
• System.out.println("centigrade (fahrenheit -
  32) 5/9")
• / Convert from fahrenheit to centigrade /
• public void fahrenToCent(int fahren)
• int cent
• cent (fahren - 32) 5 / 9
• System.out.println(fahren F -gt " cent
  C")

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Getting values into methods

• Prompting the user for values
• A statement in the method code can read a value
  that the user types in the terminal window.
• Needs a Scanner object to do the reading
• Parameters
• Declare the type and name of a variable in the
  (.) of the method.
• When the method is called, you must pass a value
  for each parameter
• Bluej lets you call a method and will ask you to
  enter the value(s)

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LabRequirements using a parameter

• public class LabRequirements
• public void printRequirements(int numStudents)
• int numStreams (numStudents 1) / 33 1
• System.out.println("number of streams "
  numStreams)
• double tutorHours numStreams 2 1.5
• System.out.println("number of tutor hours "
  tutorHours)

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Call the method printRequirements

• What happens if we call the method
• LabRequire1 . printRequirements(104)
• public void printRequirements(int numStudents)
• int numStreams (numStudents-1) / 33 1
• System.out.println("number of streams "
  numStreams)
• int tutorHours numStreams 3 2
• System.out.println("number of tutor hours "
  tutorHours)

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LabRequirements with parameters

• / Computes and prints lab requirements,
• Requires Course Code, as well as number of
  students/
• public void printRequirements (String code, int
  numStudents)
• int streams (numStudents 1) / 33 1
• double tutorHours streams 2 1.5
• System.out.printf(" s needs d streams and 4.2f
  tutor hours\n",
• code, streams,
  tutorHours)

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Syntax diagram for Methods
lttypegt
public
ltmethod namegt
void
(
)

lttypegt
ltparameter namegt
,
ltstatementgt

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Graphical Output

• Need a window on the screen
• (not the Terminal window)
• a JFrame object
• Needs an object we can call drawing methods on.
• a DrawingCanvas object
• Attached to the JFrame
• Note textbook uses an Applet object and a
  Graphics object, 2.7 2.9
• Applets are more complicated
• Same methods (almost)

JFrame JFrame-52
DrawingCanvas DrawingCanvas-6
drawRect fillRect drawLine
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Using JFrame and DrawingCanvas

• / Draw a Os and Xs board in a window on the
  screen /
• public void drawOandX()
• // set up the window and canvas
• JFrame frame new JFrame(O and X)
• frame.setSize(600, 400)
• DrawingCanvas canvas new DrawingCanvas()
• frame.getContentPane().add(canvas,
  BorderLayout.CENTER)
• frame.setVisible(true)
• // draw the board
• canvas.drawRect( , , , )
• canvas.drawLine( , , , )
• canvas.drawLine( , , , )
• canvas.drawLine( , , , )
• canvas.drawLine( , , , )

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Arguments for drawing methods

• coordinates from the left and from the top
• Lines start and end coordinates
• Shapes top, left, width, height

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Using DrawingCanvas

• Read the textbook about colours and drawing
  actions
• LL 2.7, 2.9
• Read the documentation for DrawingCanvas
• (on the Java documentation pages, off the comp102
  home page)
• Sketch what you want to draw first
• Identify the methods you will call
• Work out the arguments of the method calls.

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Drawing with variables
size

• int left 50
• int top 40
• int size 30
• int right left (size 3)
• int bot top (size 3)
• canvas.drawRect( left , top , size 3 ,
  size 3 )
• canvas.drawLine( left , top size , right
  , top size )
• canvas.drawLine( left , topsize2 , right ,
  topsize2 )
• canvas.drawLine( leftsize , top , leftsize ,
  bot )
• canvas.drawLine( leftsize2 , top ,
  leftsize2 , bot )

(left, top)
, , , ) , , , ) , , , ) , , ,
) , , , )
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Drawing with variables

• int left 50
• int top 40
• int size 30
• int right left (size 3)
• int bot top (size 3)
• canvas.drawRect( left, top, size 3, size
  3 )
• canvas.drawLine( left, topsize, right,
  topsize )
• canvas.drawLine( left, topsize2, right,
  topsize2 )
• canvas.drawLine( leftsize, top, leftsize,
  bot )
• canvas.drawLine( leftsize2, top, leftsize2,
  bot )
• left 200
• top 40
• right left (size 3)
• bot top (size 3)
• canvas.drawRect( left, top, size 3, size
  3 )
• canvas.drawLine( left, topsize, right,
  topsize )
• canvas.drawLine( left, topsize2, right,
  topsize2 )
• canvas.drawLine( leftsize, top, leftsize,
  bot )
• canvas.drawLine( leftsize2, top, leftsize2,
  bot )

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Libraries

• Your program must specify all the libraries that
  you use
• import comp100.
• import java.util.
• import javax.swing.
• import java.awt.BorderLayout

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Drawing with variables

• Draw two boards, one at (10, 10) and another at
  (200, 10)
• public void drawOandX()
• JFrame frame new JFrame(O and X)
• frame.setSize(600, 400)
• DrawingCanvas canvas new DrawingCanvas()
• frame.getContentPane().add(canvas,
  BorderLayout.CENTER)
• frame.setVisible(true)
• // draw the boards
• this.drawBoard(10, 10, canvas)
• this.drawBoard(200, 10, canvas)
• Calling another method on the same object
• Passing two different sets of arguments

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Drawing with variables

• public void drawBoard(int left, int top,
  DrawingCanvas canvas)
• int size 30
• int right left (size 3)
• int bot top (size 3)
• canvas.drawRect( left , top , size 3 ,
  size 3 )
• canvas.drawLine( left , top size , right
  , top size )
• canvas.drawLine( left , topsize2 , right ,
  topsize2 )
• canvas.drawLine( leftsize , top , leftsize ,
  bot )
• canvas.drawLine( leftsize2 , top ,
  leftsize2 , bot )

, , , ) , , , ) , , , ) , , ,
) , , , )
(left, top)
size
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Review of Scanner

• Input from user via terminal window
• Make a Scanner object that wraps up System.in
• Use System.out.print() callsto prompt the
  user for the next value.
• Call next(), nextInt(), nextDouble(), nextLine()
  etcto get the next value the user typed.
• Scanner scan new Scanner ( System.in )
• System.out.print( Enter name )
• String name scan.nextLine( )
• System.out.print( Enter age )
• int age scan.nextInt( )

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Methods on Scanner objects

• Look up the Documentation!
• A Scanner breaks its input into tokens
• (strings of characters separated by whitespace)
• Some methods on Scanner objects
• public String next ( ) get and return next token
  as a String
• public int nextInt ( ) get and return next token
  as an int (if its an integer)
• public double nextDouble ( ) get and return next
  token as a double (if its a double)
• public String nextLine() get and return rest of
  line as a String.
• Note, these methods return a value!
• type of value returned is specified by the type
  before method name

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Methods that return values.

• If methods return a value, you can use the value
• String ans scan.next ( )
• int age scan.nextInt ( )
• System.out.println(n scan.nextLine ( ))
• You can ignore the value
• scan.nextLine() // read and throw away the
  rest of the line.
• Methods can return a value and/or have some
  effect
• the return type of the method says what kind of
  value it returns
• PrintStream public void println ( String str )
  
• Scanner public int nextInt ( ) .
• public String nextLine ( ) .
• public boolean hasNextInt ( ) .
• public void close ( ) .

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? More kinds of Expressions

• Calls to Methods that return a value
• scan.nextInt()
• scan.next()
• scan.nextLine()
• Creating a new object
• new Scanner(System.in)
• new LabRequirements()

ltClass namegt
(
)
new
ltargumentgt
,
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Input and Output

• Output
• Use the System.out object to print on the
  terminal window
• Use a DrawingCanvas object to draw graphics in a
  window
• Use fancy user interface objects, like
  JOptionPane.
• Input
• Use Bluejs special facilities for calling
  methods with arguments
• Use a Scanner object and the System.in object to
  get input from user typing in the terminal
  window.
• Use fancy user interface objects, like
  JOptionPane
• Use even fancier user interface objects to
  getinput from the mouse, buttons, sliders, etc

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Input and Output

• Output
• Use the System.out object to print on the
  terminal window
• Use a DrawingCanvas object to draw graphics in a
  window
• Use fancy user interface objects, like
  JOptionPane.
• Input
• Use Bluejs special facilities for calling
  methods with arguments
• Use a Scanner object and the System.in object to
  get input from user typing in the terminal
  window.
• Use fancy user interface objects, like
  JOptionPane
• Use even fancier user interface objects to
  getinput from the mouse, buttons, sliders, etc

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