CS 180

1

• CS 180
• Recitation 9/22/06

2
Announcements

• Exam 1 is Wednesday, September 27th
• Room EE170
• Time 700 800 pm
• If you have a conflict with the exam, contact Dr.
  Van Zandt
• Sign the Academic Integrity Policy!!
• Project 3 due Thursday, September 28th
• There have been updates to the description

3
Boolean Expressions

• boolean is a primitive data type
• Two values true or false
• Compares two values using a relational expression
• lt, gt, , lt, gt, !
• Examples
• boolean isOK true
• boolean isLarge num gt 100

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Boolean Operators

• Boolean expressions can be combined using boolean
  operators
• And
• Or
• Not !

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Boolean Operators

• bool1 bool2
• true if bool1 AND bool2 are true
• false if either bool1 or bool2 is false
• bool1 bool 2
• true if either bool1 OR bool2 is true
• false if both bool1 AND bool2 are false
• !bool1
• true if bool1 is false
• false if bool1 is true

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Boolean Operator Examples
int x 20 boolean isValid x gt 0 x lt
100 int x 5 boolean isValid x gt 0 x lt
-100 int x 5 int y 10 boolean isDouble
(y (x 2))

• What are the results of the above expressions?

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Operator Precedence

• Parenthesis should be used to indicate the order
  of operations
• When there are no parenthesis, operator
  precedence is followed
• Higher precedence preformed before lower
  precedence
• Equal precedence performed left-to-right, except
  for unary operations which are performed
  right-to-left

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Operator Precedence Rules
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Operator Precedence Examples
int x 20 5 10 int y (20 5)
10 boolean w true true false
false boolean z true (true false)
false

• What are the values of x, y, w, and z?

10
Selection Statements

• Selection statements change the flow of control
  in a program
• Use when the action to be preformed is dependent
  on the answer to a question
• E.g. If the value of x is less than zero, print
  an error message. Otherwise add 1

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If-else Statement

• A branching statement used to choose between two
  actions

if ( ltBoolean expressiongt ) ltthen blockgt else
ltelse blockgt

• The else branch is optional

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If-else Statement

• To enclose multiple statements in a branch,
  enclose the branch in braces

if ( ltBoolean expressiongt ) line 1 line
2 line 3 else line 4 line 5
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If-else Statement

• Single line blocks are not required to be
  enclosed in braces, but it is a good idea

if ( ltBoolean expressiongt ) ltthen blockgt else
ltelse blockgt
Is equivalent to
if ( ltBoolean expressiongt ) ltthen
blockgt else ltelse blockgt
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Multibranch If-else Statement
if ( ltBoolean Expression 1gt ) statement 1 else
if (Boolean Expression 2) statement 2 else if
(Boolean Expression 3) statement 3 else if
(Boolean Expression 4) statement 4 else Default
Statement
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If-else Statement Examples
int grade 11 if (grade lt 5 grade gt 10)
grade else grade--
int grade 70 if (count gt 90 count lt 100)
System.out.println(A) else if(count gt
80) System.out.println(B) else if(count gt
70) System.out.println(C) else if(count gt
60) System.out.println(D) else System.out.pri
ntln(F)

• What is the value of grade in each statement?

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If-else Statement Examples
int grade 5 if(grade lt 5) grade grade
10
int grade 5 if(grade lt 5) grade grade
10

• What is the value of grade in each statement?

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If-else Statement Examples
int grade 5 if(grade lt 5) grade 10
int grade 5 if(grade gt 0) grade if(grade
gt 5) grade else grade 0

• What is the value of grade in each statement?

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Switch Statements

• Switch statements are a multiway branch which
  makes its decision based on an integer expression
• char, byte, short, or int
• A list of cases is searched until a match is
  found
• If no match is found, the default case is
  executed
• Optional

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Switch Statement Syntax
switch(Controlling_Expression) case
Label1 statement(s) ltbreakgt case
Label2 statement(s) ltbreakgt ltdefaultgt s
tatement(s)

• The breaks and the default case label above are
  optional
• What happens if we take the breaks out?

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Switch Statement Examples
int section 7 int room 0 switch(section)
case 1 room 101 break case 7 room
102 break case 5 room
103 break default System.out.println(inval
id)
int section 7 int room 0 switch(section)
case 1 room 101 break case 7 room
102 case 5 room 103 default System.out.p
rintln(invalid)

• What are the results of the above statements?

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Switch Statement Examples
char gender f switch(section) case
f case F System.out.println(female)
break case m case M System.out.println(
male) break

• What is the result of the above statement?
• Notice the empty case bodies
• What if gender x ?

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Drawing Graphics

• Chapter 5 introduces four standard classes
  related to drawing geometric shapes. They are
• java.awt.Graphics
• java.awt.Color
• java.awt.Point
• java.awt.Dimension
• These classes are used in the Sample Development
  section
• Please refer to Java API for details

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Sample Drawing
import javax.swing. //for JFrame import
java.awt. //for Graphics and Container class
Ch5SampleGraphics public static void main(
String args ) JFrame win
Container contentPane Graphics g
win new JFrame("My First Rectangle")
win.setSize(300, 200)
win.setLocation(100,100)
win.setVisible(true) contentPane
win.getContentPane() g
contentPane.getGraphics()
g.drawRect(50,50,100,30)
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The Effect of drawRect
graphic.drawRect(ltxgt, ltygt, ltwidthgt, ltheightgt)
graphic.drawRect(50,50,100,30)
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Problem Statement

• Write an application that simulates a
  screensaver by drawing various geometric shapes
  in different colors. The user has an option of
  choosing a type (ellipse or rectangle), color,
  and movement (stationary, smooth, or random).

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Overall Plan

• Tasks
• Get the shape the user wants to draw.
• Get the color of the chosen shape.
• Get the type of movement the user wants to use.
• Start the drawing.

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Required Classes
standard class
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Development Steps

• We will develop this program in six steps
• Start with a program skeleton. Explore the
  DrawingBoard class.
• Define an experimental DrawableShape class that
  draws a dummy shape.
• Add code to allow the user to select a shape.
  Extend the DrawableShape and other classes as
  necessary.
• Add code to allow the user to specify the color.
  Extend the DrawableShape and other classes as
  necessary.
• Add code to allow the user to specify the motion
  type. Extend the DrawableShape and other classes
  as necessary.
• Finalize the code by tying up loose ends.

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Step 1 Design

• The methods of the DrawingBoard class
• public void addShape(DrawableShape shape)
• Adds a shape to the DrawingBoard. No limit to
  the number shapes you can add
• public void setBackground(java.awt.Color color)
• Sets the background color of a window to the
  designated color
• public void setDelayTime(double delay)
• Sets the delay time between drawings to delay
  seconds
• public void setMovement(int type)
• Sets the movement type to STATIONARY, RANDOM, or
  SMOOTH
• public void setVisible(boolean state)
• Sets the background color of a window to the
  designated color
• public void start( )
• Starts the drawing of added shapes using the
  designated movement type and delay time.

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Step 1 Code
Directory Chapter5/Step1 Source Files
Ch5DrawShape.java
Program source file is too big to list here. From
now on, we ask you to view the source files using
your Java IDE.
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Step 1 Test

• In the testing phase, we run the program and
  verify that a DrawingBoard window with black
  background appears on the screen and fills the
  whole screen.

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Step 2 Design

• Define a preliminary DrawableShape class
• The required methods of this class are
• public void draw(java.awt.Graphics g)
• Draws a shape on Graphics object g.
• public java.awt.Point getCenterPoint( )
• Returns the center point of this shape
• public java.awt.Dimension getDimension( )
• Returns the bounding rectangle of this shape
• public void setCenterPoint(java.awt.Point pt)
• Sets the center point of this shape to pt.

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Step 2 Code
Directory Chapter5/Step2 Source Files
Ch5DrawShape.java DrawableShape.java
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Step 2 Test

• We compile and run the program numerous times
• We confirm the movement types STATIONARY, RANDOM,
  and SMOOTH.
• We experiment with different delay times
• We try out different background colors

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Step 3 Design

• We extend the main class to allow the user to
  select a shape information.
• We will give three choices of shapes to the user
  Ellipse, Rectangle, and Rounded Rectangle
• We also need input routines for the user to enter
  the dimension and center point. The center point
  determines where the shape will appear on the
  DrawingBoard.
• Three input methods are
• private int inputShapeType( )
• private Dimension inputDimension( )
• private Point inputCenterPoint( )

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Step 3 Code
Directory Chapter5/Step3 Source Files
Ch5DrawShape.java DrawableShape.java
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Step 3 Test

• We run the program numerous times with different
  input values and check the results.
• Try both valid and invalid input values and
  confirm the response is appropriate

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Step 4 Design

• We extend the main class to allow the user to
  select a color.
• We follow the input pattern of Step 3.
• We will allow the user to select one of the five
  colors.
• The color input method is
• private Color inputColor( )

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Step 4 Code
Directory Chapter5/Step4 Source Files
Ch5DrawShape.java DrawableShape.java
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Step 4 Test

• We run the program numerous times with different
  color input.
• Try both valid and invalid input values and
  confirm the response is appropriate

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Step 5 Design

• We extend the main class to allow the user to
  select a movement type.
• We follow the input pattern of Step 3.
• We will allow the user to select one of the three
  movement types.
• The movement input method is
• private int inputMotionType( )

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Step 5 Code
Directory Chapter5/Step5 Source Files
Ch5DrawShape.java DrawableShape.java
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Step 5 Test

• We run the program numerous times with different
  movement input.
• Try both valid and invalid input values and
  confirm the response is appropriate

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Step 6 Finalize

• Possible Extensions
• Morphing the object shape
• Changing the object color
• Drawing multiple objects
• Drawing scrolling text