Bobby D. Gerardo

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Programming and Problem Solving Using Java

• Bobby D. Gerardo
• Kunsan National University
• Summer 2004

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Chapter 3Object Oriented Design and Writing
Worker Class
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Review
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Class Definition

• A Class Definition has the following form
• A header declaration
• The class body
• The data field declaration of the class
• The method definition of the class
• Form visibility class classname
• Example public class PiglatinApp

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Definition of Method main()

• Method main() has always the following header
• public static void main(String args)
• public can be accessed outside of the class
  main()
• static means that main() is not applied to an
  object when it is invoked. (Applied for a
  class)
• void means that main() does not return a result
  but is executed for its effect

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Case Study Solution Format

1. Problem specify the problem requirement
2. Analysis analyze the problem an identify the
   classes that will be needed
3. Design design the classes to solve the problem.
   Locate the relevant classes in libraries. Modify
   existing classes if necessary. Design new classes
   where necessary
4. Implementation implement the new and modified
   classes.
5. Testing test and verify the completed program.

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Review Exercise
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Review Exercise

• List 4 kinds of primitive data
• Indicate whether each assignment is valid or not
  valid.
• r 3.5 5.0
• i 2 5
• char c my name
• int i double r
• Write an assignment in java x (ab)2(cd)
• Evaluate the following
• Value of x is 57
• Value of x is 5 7
• This String.charAt(1)

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Selected Programming Solution1. Math Class and
Pow Method2. Solution of a Distance Problem3.
Demo of House Cost
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The Math Class and Pow Method
Bank Calculator example Formula, balanceN
balance(1InterestRate)2 In Java, balanceN
balance( (1InterestRate) (1InterestRate)
Modified Bank Calculator using pow(x, y)
method Formula, balanceN balance(1InterestRat
e)2 In Java, R 1 InterestRate balanceN
Balance Math.pow(R, 2)
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Solution of a Distance Problem
Java Code X (X2-X1) Y (Y2-Y1)
D Math.sqrt(Math.pow(X, 2) Math.pow(Y, 2))
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Chapter 3Object Oriented Design and Writing
Worker Class
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Object Oriented Design-outline

• Object oriented design write classes that
  define methods and perform different kinds of
  operation.
• Worker classes are also called support classes
  because they support application class or client
  class.
• Java Abstract Window Toolkit (AWT)
• Incorporate Java Applet in HTML file.

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3.1. A First Worker Class Class FoodItem

• The data field of a class (also called instance
  variables) store the information associated with
  an object of that class.
• The fields maybe referenced through out the class
• The values stored in an objects data fields
  represent the state of that object.

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3.1. Class FoodItem (cont)

• Declare Class FoodItem and its three data fields.
• Giving data fields initial value.
• Method main definitions.
• Methods for the class FoodItem.
• Constructor- create new FoodItem objet
• Object mutators- change the descriptors, size,
  price
• Accesors- return the description, size, price
• Method that returns the object state as a string
• A method that calculates the unit price of an
  item

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3.1. Class FoodItem (cont)

• Table 3.1 Method headers for FoodItem
• Constructor method
• void Methods- mutator methods are all void
  methods.
• The return statement method that is not a void
  method or constructor returns a single result.
• Post conditions a condition that must be true
  after the method executes and is part of the
  class documentation.
• Note We will demo the class FoodItem and
  TestFoodItem

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Arguments are Passed by a value

• In Java, primitive type arguments are passed by
  value.
• This means that the value of each argument is
  passed to each corresponding parameter and a
  separate copy of that value is stored locally in
  the method parameter.
• Note see Fig. 3.4

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Transfer of Control during Method Call and Return

• During compilation of a class, each method is
  translated into a sequence of byte code
  instruction.
• Each call to a method is translated as an
  instruction that transfers control to the byte
  code instruction for that method.
• When the compiler reaches the end of method
  definition, it inserts an instruction returning
  control from he method back to the calling
  instruction.
• Note Fig. 3.5 show the transfer of control that
  occurs when the main method in Fig. 3.2 executes
  that statement.

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Encapsulation

• Because all data fields have private visibility
  (FoodItem Example), another class that is a
  client (user) of the class FoodItem cannot access
  the field directly.
• To change the data field value, the client must
  invoke one of the mutator methods.
• To retrieve a data field value, the client must
  invoke one of the accesor methods.
• This is the principle of encapsulation.
• Note see Fig. 3.6

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Case Study 1 Finding the Words in a Sentence
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Case Study 1 Finding the Words in a Sentence

• 1. Problem Write a program that gets a sentence
  and displays the first three words in the
  sentence on separate lines
• 2. Analysis analyze the problem an identify the
  classes that will be needed
• 3. Design design the classes to solve the
  problem. Locate the relevant classes in
  libraries. Modify existing classes if necessary.
  Design new classes where necessary
• 4. Implementation implement the new and
  modified classes.
• 5. Testing test and verify the completed
  program.

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Modified Finding the Words in a Sentence

• Modify the case study Finding the Words in a
  Sentence to show the output on a dialog window.
  Note, this is to use java.swing.

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Case Study 2 Designing a Coin Changer
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Case Study2 Designing a Coin Changer

• 1. Problem Determine the value of collection
  coins. Our goal is to write a class that
  simulates the behavior of a coin changer. Instead
  of pouring a container of coins into a hopper,
  the user will provide the number of each kind of
  coin as input data.
• 2. Analysis analyze the problem an identify the
  classes that will be needed
• 3. Design design the classes to solve the
  problem. Locate the relevant classes in
  libraries. Modify existing classes if necessary.
  Design new classes where necessary
• 4. Implementation implement the new and
  modified classes.
• 5. Testing test and verify the completed
  program.

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Modified Designing a Coin Changer

• Modify the case study Finding the Words in a
  Sentence to add the method to a class
  CoinChanger that dispenses change using the
  fewest coins. For example, if the value computed
  for change is 92 cents, this method should return
  a String object that contains the characters.
• quarter 3, dimes 1, nickels 1, pennies 2

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Programming Projects(1) Case 1 Finding the
Words in a Sentence, P.120(2) Modified
Finding the Words in a Sentence(3) Case 2
Coin Changer, P. 127 (4) Modified Coin Changer,
Prog. 1, P.134Note Morning Programming
Exercises
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Case Study 3 Computing the Weight of Flat
Washers
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Case Study 3 Computing the Weight of Flat
Washers

• 1. Problem You work for a company that
  manufactures flat washers. To estimate shipping
  costs, you need a program that computes the
  weight of a specified quantity of flat washers.
  As part of this process, you need to compute the
  weight of a single washer.
• 2. Analysis analyze the problem an identify the
  classes that will be needed
• 3. Design design the classes to solve the
  problem. Locate the relevant classes in
  libraries. Modify existing classes if necessary.
  Design new classes where necessary
• 4. Implementation implement the new and
  modified classes.
• 5. Testing test and verify the completed
  program.

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Modified Computation of the Weight of Flat
Washers

• Modify the case study Computing the Weight of
  Flat Washers by including the following
• Data inputs shall be in radius rather than in
  diameter.
• Put a dialog box prompting a message that the
  input inner radius is larger than the outer
  radius.

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Summary of Programming Projects(1) Case 1
Finding the Words in a Sentence, P.120(2)
Modified Finding the Words in a
Sentence(3) Case 2 Coin Changer, P. 127 (4)
Modified Coin Changer, Prog. 1, P.134(5) Case 3
Computing the Weight of Flat Washers (6)
Modified Computation of the weight of
Flat washers
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Review of Methods

• Constructor Methods always has the same name as
  the class. It should have the public visibility
  and does not have a result type because it does
  not return a value. Fig. 3.17
• Accessor Methods accessor methods are sometimes
  called getter methods and should begin with the
  word get. Fig. 3.18
• Mutator Methods Just as we need to access an
  objects private o protected data from another
  object, we sometimes need to store data in an
  objects private or protected fields. We use
  mutator or modifier methods to do this. Fig. 3.19

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String Objects are Immutable

• Unlike the classes that we define ourselves,
  String objects are immutable which means that we
  cannot change the characters stored in a String
  object.
• If we do so Java creates a new String object that
  store the modified string. Fig. 3.20

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Table 3.5 Some formatting patterns for class
DecimalFormat
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Table 3.6 Class DecimalFormat methods
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Table 3.7 Class NumberFormat Methods
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Table 3.8 Class KeyIn methods for reading data
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Applets, AWT, and the Graphics Class

• Java provides a collection of graphics methods
  that enable you to draw pictures or graphical
  patterns on a drawing surface such as a computer
  screen.
• You can draw lines and geometric shapes.
• You can specify the position of each shape and
  also its color.

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The Drawing Surface

• In graphics programming you can control the
  location on a drawing surface of each line or
  shape that you draw.
• You must know the size of your drawing surface
  and how to reference picture elements (pixels) on
  it.
• Fig. 3.32

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The AWT Class Library

• Abstract Window Toolkit (AWT) to facilitate
  graphics and GUI programming.
• If you wish to draw you must import the AT
  package java.awt.
• AWT contains a hierarchy of classes for
  displaying windows and GUI components.
• An application class is completely self
  sufficient entity that may rely on support
  objects to do its job.

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The AWT Class Library (cont)

• An application class is completely self
  sufficient entity that may rely on support
  objects to do its job.
• An applet is not self-sufficient. It is intended
  as a support object in a larger context such as
  web browser like IE or Netscape.
• Fig. 3.33., two files play important role,
  htmlFileName and className.

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Graphics programming Exercises

• Figure 3.34 P. 159
• Modify Fig. 3.34 to draw Red and blue lines at
  position 240X340

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Drawing Rectangles

• You can use method drawRect() (defined in class
  Graphics) to draw rectangle on the screen. i.e.
• g.drawRect(x1, y1, 100, 50)
• Fig. 2.36 Rectangle with (x1, y1) as top to left
  corner.

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Graphics programming Exercises

• Figure 3.37 P. 162- Class House
• Modify Fig. 3.37 to use brown lines and red door.

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Drawing Arcs and Circles

• Method drawArc() draws an arc. The method call is
• g.drawARc(x, y, 100, 100, 0, 90)
• Fig. 3.40 show the Arc drawn by the previous
  statement
• Circle
• g.drawOval(x, y, 100, 100)
• g.drawArc(x, y, 100, 100, 0, 360)

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Circle with Point (x, y)

• A circle with center at point (x, y) and radius r
  could be drawn inside a square whose top-left
  corner is at point (x-r, y-r).
• g.drawOval (x-r, y-r, 2r, 2r)
• Fig. 3.41

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Graphics programming Exercises

• Figure 3.42 P. 166- Class HappyFace
• Modify Fig. 3.42 with eyes and nose filled with
  yellow color.

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Drawing Pie Slices

• Java Provides methods to draw pie slices
• A pie slice is filled segment of a circle. The
  method call is
• g.fillArc(x-r, y-r, 2r, 2r, 20, 30)
• Fig. 3.44 A Pie Slice

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Programming Projects

1. No.1 P. 177 Projectile Problem
2. No. 7 P. 179 Bar Graph.

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Summary of Programming Exercises and Projects

• Exercises
• Figure 3.34 P. 159
• Modify Fig. 3.34 to draw Red and blue lines at
  position 240X340
• Figure 3.37 P. 162- Class House
• Modify Fig. 3.37 to use brown lines and red door.
• Figure 3.42 P. 166- Class HappyFace
• Modify Fig. 3.42 with eyes and nose filled with
  yellow color.
• Projects
• No.1 P. 177 Projectile Problem
• No. 7 P. 179 Bar Graph.

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? End of Chapter