Java Programming, 3e Concepts and Techniques Chapter 4 Decision Making and Repetition with Reusable Objects

Chapter 4: Decision Making and Repetition with Reusable Objects 2 Chapter Objectives Design a program using methods Code a selection structure to make decisions in code Describe the use of the logical AND, OR, and NOT operators Define exceptions and exception handling

Chapter 4: Decision Making and Repetition with Reusable Objects 3 Chapter Objectives Code a try statement and a catch statement to handle exceptions Create a user-defined method Code a repetition structure using the while statement Write a switch statement to test for multiple values in data

Chapter 4: Decision Making and Repetition with Reusable Objects 4 Chapter Objectives Format numbers using a pattern and the format() method Construct a Color object Use a Checkbox and a CheckboxGroup in the user interface

Chapter 4: Decision Making and Repetition with Reusable Objects 5 Introduction Control structures alter the sequential execution of code –Selection structure –Repetition structure User-defined methods break tasks into reusable sections of code Exception handling in Java allows for the testing of valid and accurate input

Chapter 4: Decision Making and Repetition with Reusable Objects 6 The Sales Commission Program Calculate sales commission for agents in a travel agency Coded as a console application and an applet Input –The user chooses from three types of commission codes The commission code identifies the type of sale and the commission rate –The user enters a sales amount Calculate commission and display output

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8 Program Development Problem analysis –Each user decision corresponds to a program task –Develop and test each task before adding it to the program Design the solution –Design storyboards for the two user interfaces Program design –Design a flowchart consisting of required methods –Write related pseudocode for each method Validate Design

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10 Coding the Program Code the program using program stubs –Stubs are incomplete portions of code that serve as a template or placeholder for later code –Stubs allow ease in debugging through incremental compilation and testing Import java.swing.JOptionPane Import java.text.DecimalFormat –Formats decimal output into Strings Declare variables Compile and test the program stub

Chapter 4: Decision Making and Repetition with Reusable Objects 11 Coding the Program

Chapter 4: Decision Making and Repetition with Reusable Objects 12 Writing Methods A program with modules allows for clarity, reusability, and refinement The code for each module can be separated into programmer-defined methods The main() method transfers execution to the methods through a call statement The called method returns control to its caller with the return statement or the ending brace –The return statement returns any required data back to the calling method

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Chapter 4: Decision Making and Repetition with Reusable Objects 14 The if…else Statement Single: line 30, line 31 Block: lines 15-27, lines 19-20, lines Nested: lines 17-26, lines 30-31

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Chapter 4: Decision Making and Repetition with Reusable Objects 16 Testing with an if statement Testing a single condition –if (answer == null) –if (!done) Testing multiple conditions –if ((gender == “male”) && (age >= 18)) –if ((age 65)) –AND and OR expressions evaluate the right operand only if the left operand is not sufficient to decide the condition

Chapter 4: Decision Making and Repetition with Reusable Objects 17 Exception Handling An exception is an event resulting from an erroneous situation which disrupts normal program flow Exception handling is the concept of planning for possible exceptions by directing the program to deal with them gracefully, without terminating Three kinds of exceptions –I/O –Run-time –Checked The compiler checks each method to ensure each method has a handler

Chapter 4: Decision Making and Repetition with Reusable Objects 18 Handling Exceptions The try statement identifies a block of statements that may potentially throw an exception The throw statement transfers execution from the method that caused the exception to the handler –Transfers execution to the catch statement if the throw is placed within a try statement The catch statement identifies the type of exception being caught and statements to describe or fix the error The finally statement is optional and is always executed regardless of whether an exception has taken place –Placed after the catch statement

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Chapter 4: Decision Making and Repetition with Reusable Objects 21 Catch an exception Throw an exception

Chapter 4: Decision Making and Repetition with Reusable Objects 22 Throwing an Exception Compile the program after coding each method and call statement Run the program with correct input Run the program to test the exception handling with invalid input –Alphabetic data –Negative values –Null or zero values Verify that the user is allowed to reenter data Verify the program closes correctly

Chapter 4: Decision Making and Repetition with Reusable Objects 23 Repetition Structure

Chapter 4: Decision Making and Repetition with Reusable Objects 24 The getSales() method

Chapter 4: Decision Making and Repetition with Reusable Objects 25 The getCode() method

Chapter 4: Decision Making and Repetition with Reusable Objects 26 The Case Structure A type of selection structure that allows for more than two choices when the condition is evaluated Used when there are many possible, valid choices for user input The code evaluates the user choice with a switch statement and looks for a match in each case statement Each case statement contains a ending break statement which forces exit of the structure

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Chapter 4: Decision Making and Repetition with Reusable Objects 28 The getComm() Method

Chapter 4: Decision Making and Repetition with Reusable Objects 29 Arguments and Parameters When a method is called, the calling method sends arguments; the called method accepts the values as parameters Different but related identifier names for the arguments and the parameters should be used for good program design –The variables are only visible in their respective methods Arguments and parameters for a called method and the calling statement must be of the same number, order, and data type

Chapter 4: Decision Making and Repetition with Reusable Objects 30 Formatting Numeric Output The DecimalFormat class formats decimal numbers into Strings for output Supports different locales, leading and trailing zeros, prefixes/suffixes, and separators The argument is a pattern, which determines how the formatted number should be displayed

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Chapter 4: Decision Making and Repetition with Reusable Objects 32 The output() method

Chapter 4: Decision Making and Repetition with Reusable Objects 33 The finish() method Exits system when program completes successfully

Chapter 4: Decision Making and Repetition with Reusable Objects 34 Moving to the Web Create the host document to execute the applet

Chapter 4: Decision Making and Repetition with Reusable Objects 35 Coding an Applet Stub Enter general block comments Import java.awt.*, java.applet.*, java.awt.event.*, and java.text.DecimalFormat Implement the ItemListener interface to listen for the user choice on a Checkbox Code the method headers for the init() and the itemStateChanged() method –itemStateChanged() is an ItemListener method to process user choices Declare variables and construct a Color object

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Chapter 4: Decision Making and Repetition with Reusable Objects 37 Making Decisions in Applets Use a CheckboxGroup to allow user choices

Chapter 4: Decision Making and Repetition with Reusable Objects 38 Constructing Applet Components Construct Labels for input and output Construct a CheckboxGroup for user options

Chapter 4: Decision Making and Repetition with Reusable Objects 39 Constructing Applet Components Add Labels and CheckboxGroup to the applet Add an ItemListener to each Checkbox component with the addItemListener() method Add color with the setForeground() and the setBackground() methods Set the insertion point with the requestFocus() method

Chapter 4: Decision Making and Repetition with Reusable Objects 40 The init() Method

Chapter 4: Decision Making and Repetition with Reusable Objects 41 Handling Exceptions Check for valid data when the itemStateChanged() method is triggered, which happens when the user clicks an option button

Chapter 4: Decision Making and Repetition with Reusable Objects 42 The getSales() Method Parse the data from the TextField and return a valid sales amount or throw an exception to the init() method

Chapter 4: Decision Making and Repetition with Reusable Objects 43 The getCode() Method Initialize the code to 0 Use nested if statements to assess the boolean state of the Checkboxes and return the code to init()

Chapter 4: Decision Making and Repetition with Reusable Objects 44 The getComm() Method Identical to the application Return the commission value to init()

Chapter 4: Decision Making and Repetition with Reusable Objects 45 The output() Method Send output to the Label using setText() Construct and use DecimalFormat, using the special character # to make a leading zero absent

Chapter 4: Decision Making and Repetition with Reusable Objects 46 The paint() Method Display a graphic

Chapter 4: Decision Making and Repetition with Reusable Objects 47 Compiling and Testing the Applet Compile the applet Execute the applet using AppletViewer Test exception handling by clicking an option button and then typing invalid data into the text box Verify the error message and the data clearing mechanisms Test all options with valid data Test in a browser window Document the applet interface and source code

Chapter 4: Decision Making and Repetition with Reusable Objects 48 Chapter Summary Design a program using methods Code a selection structure to make decisions in code Describe the use of the logical AND, OR, and NOT operators Define exceptions and exception handling

Chapter 4: Decision Making and Repetition with Reusable Objects 49 Chapter Summary Code a try statement and a catch statement to handle exceptions Create a user-defined method Code a repetition structure using the while statement Write a switch statement to test for multiple values in data

Chapter 4: Decision Making and Repetition with Reusable Objects 50 Chapter Summary Format numbers using a pattern and the format() method Construct a Color object Use a Checkbox and a CheckboxGroup in the user interface

Java Programming, 3e Concepts and Techniques Chapter 4 Complete