1. Alice in Action with Java Chapter 7 From Alice to Java

2. Alice in Action with Java2 Objectives Write some first Java programs Learn the basics of the Eclipse Integrated Development Environment (IDE) Begin making the transition from Alice to Java

3. Alice in Action with Java3 From Alice to Java The four steps of computer programming –1. Designing the program –2. Writing the program –3. Running the program –4. Testing the program Program development using Alice –Step 1: Write user stories and construct storyboards –Step 2: Add objects to world, animate with messages –Step 3: Press the Play button –Step 4: Scrutinize a number of executions

4. Alice in Action with Java4 From Alice to Java (continued) Benefits of program development using Alice –3D graphics let you visualize programming concepts –Drag-and-drop coding reduces syntax errors Benefits of program development using Java –Build reusable classes –Run Java programs across various platforms –Build applets to make Web pages interactive

5. Alice in Action with Java5 Designing a First Java Program Use many techniques learned in Alice First step: write a user story to help setup structure User story for dollars-to-euros currency conversion –Query user for dollar amount to convert to euros –Read the dollar amount from the user –Query user for euros-per-dollar exchange rate –Read euros-per-dollar exchange rate –Compute corresponding number of euros –Display dollar and (computed euros values)

6. Alice in Action with Java6 The Object List Review: class is blueprint for an object Procedure for isolating objects in the user story –Identify the noun phrases (primary object indicators) –Create a table listing nouns, values stored, and names The name should also be a noun (or noun phrase) The name should be descriptive –If no Java type matches the value, define a class Naming convention –Class: capitalize each word in the name –Variable or method: capitalize each word except first

7. Alice in Action with Java7 The Object List (continued)

8. Alice in Action with Java8 The Operations List Operations correspond to verb phrases in user story Procedure for isolating verbs in the user story –Identify the verb phrases (primary operation indicators) –Create a table listing verbs and matching operations There are five verb phrases in the user story

9. Alice in Action with Java9 The Operations List (continued)

10. Alice in Action with Java10 The Algorithm Algorithm: sequence of steps that solve a problem Algorithm for converting dollars to euros –1. Display "How many dollars do you want to convert?" –2. Read dollars –3. Display "What is the euros-per-dollar exchange rate?" –4. Read eurosPerDollar –5. Compute euros = dollars * eurosPerDollar –6. Display dollars and euros, plus descriptive labels

11. Alice in Action with Java11 Writing a First Java Program Integrated development environment (IDE) –Program editor –Compiler –Run-time environment –Debugger Some features of the Alice IDE –World window, object tree, editing area, Play button Eclipse –Free IDE for various languages developed by IBM –Java programs in this text are built using Eclipse

12. Alice in Action with Java12 Starting Eclipse Double-click eclipse.exe or eclipse shortcut –Select a folder to hold your Java programs Items in the first time welcome screen –An overview of Eclipse –Tutorials for using Eclipse –Some code samples –A summary of what’s new in the current edition The Eclipse IDE is divided into several regions

13. Alice in Action with Java13 Starting Eclipse (continued)

14. Alice in Action with Java14 Writing a Java Program Using Eclipse Creating a project –Select File->New->Project from the menu bar New Project dialog box opens –Make sure that Java Project is selected –Click the Next button New Java Project dialog box opens –Enter a descriptive name –Click the Finish button After clicking the Finish, the main window reappears –The new project appears in the package explorer area

15. Alice in Action with Java15 Writing a Java Program Using Eclipse (continued)

16. Alice in Action with Java16 Writing a Java Program Using Eclipse (continued)

17. Alice in Action with Java17 Writing a Java Program Using Eclipse (continued) All Java programs are classes Creating the DollarsToEurosConverter class –Select the project in the package explorer area –Select File->New->Class The New Java Class dialog box opens –Type DollarsToEurosConverter as the name –Ensure Public static void main() is checked –Click the Finish button After the class has been created, enter program code –Lines in main() correspond to steps in the algorithm

18. Alice in Action with Java18 Writing a Java Program Using Eclipse (continued)

19. Alice in Action with Java19 Writing a Java Program Using Eclipse (continued)

20. Alice in Action with Java20 Compiling a Java Program Using Eclipse Java compiler: checks a program for syntax errors Invoke the compiler by saving your program How the Java compiler reports errors –Error symbol displayed next to problem statement –Error is listed in the problems & output area Example of an error: omit semicolon after statement –The compiler marks the line as an error –Error details are shown in the problems & output area All errors must be fixed before you can run a program

21. Alice in Action with Java21 Compiling a Java Program Using Eclipse (continued)

22. Alice in Action with Java22 Running a Java Program Using Eclipse Running your program the first time –Choose the Run->Run... menu choice The Run dialog box opens –Ensure Java Application is selected –Click New button below Configurations column A new Java Application run configuration appears –Ensure project is listed in the box below Project –Use Search to identify class containing main() –Click the Apply button and then click Run Initiate future executions by simply clicking Run

23. Alice in Action with Java23 Running a Java Program Using Eclipse (continued)

24. Alice in Action with Java24 Running a Java Program Using Eclipse (continued)

25. Alice in Action with Java25 Running a Java Program Using Eclipse (continued)

26. Alice in Action with Java26 Testing a Java Program Using Eclipse Functional testing –Running a program multiple times, using various values –Example: use various dollar values and exchange rates Sanity checking: testing with easily verified values Logic error: problem with the program structure User testing –Utilizing another person to uncover hidden flaws –Example: roommate reveals euros formatting error Solution: use printf() to round off values of euros

27. Alice in Action with Java27 Testing a Java Program Using Eclipse (continued)

28. Alice in Action with Java28 Java Basics Strategy: compare the first program to the algorithm References –Algorithm developed in Section 7.1 –DollarsToEurosConverter.java in Figure 7-20

29. Alice in Action with Java29 Java Basics (continued)

30. Alice in Action with Java30 Comments Comments: explanatory remarks Comments are ignored by the Java compiler Three different kinds of comments –Inline: begins comment with // and ends at line’s end –Block (C-style): begins with /* and ends with */ –Javadoc: begins with /** and ends with */ Opening comments of converter are Javadoc type –Every file should have an opening comment In general, add comments to improve readability

31. Alice in Action with Java31 Import Statements and Packages Package: group of related, predefined classes –Example: Scanner class is in java.util package Access packaged classes with an import statement –Place import statements before class declaration –Example: import java.util.Scanner; Wild-card import statement –Used to import all of the classes in a package –Example: import java.util.*; java.lang contains commonly used classes –Automatically imported into a program

32. Alice in Action with Java32 The Simplest Java Program Consists of a class and an empty main() method General pattern used to define a class: public class NameOfTheClass { } –The word public makes the class visible to users –The word class indicates a new type name follows Every Java program needs a main() method The main() method is defined within the class body main() is like myFirstMethod() in Alice

33. Alice in Action with Java33 The Simplest Java Program (continued)

34. Alice in Action with Java34 The Simplest Java Program (continued) Understanding the structure of the main() method –public allows method to be invoked outside class –static indicates that main() belongs to the class –void indicates that main() does not return a value –main is the name of the method –String[]args provides a way to pass values –Statements placed within body are delimited by { and } Adding Java statements using Eclipse –Type or paste statements into the editing area –Differs from drag-and-drop style used in Alice

35. Alice in Action with Java35 Some Java Statements Technique for writing a program –Go through an algorithm step by step –Translate each step into an equivalent Java statement Goal: apply technique to dollars-to-euros algorithm Step 1 –Display "How many dollars do you want to convert?” –Use System.out.print(String query) Step 2 –Read dollars –Use a Scanner object to retrieve value from keyboard

36. Alice in Action with Java36 Some Java Statements (continued) Step 3 –Display "What is the euros-per-dollar exchange rate?” –Use System.out.print(String query) Step 4 –Read eurosPerDollar –Reuse the Scanner object from Step 2 Step 5 –Compute euros = dollars * eurosPerDollar –Assign the value in the expression to euros variable –double euros = dollars * eurosPerDollar;

37. Alice in Action with Java37 Some Java Statements (continued) Step 6 –Display dollars and euros, plus descriptive labels –Use System.out.println(String output) Concatenation operator (+) combines String values The printf() statement –Controls the format of printed values –Must have at least one argument (format-string) –Arguments after the format-string need a placeholder –Example: "%.2f dollars => %.2f euros“ Placeholder %.2f provides precision and type information

38. Alice in Action with Java38 Some Java Statements (continued)

39. Alice in Action with Java39 A Second Java Program Problem: how to determine relative value Scenario 1 –Regular size cereal costs $2.90 per 12 ounces –Economy size cereal costs $4.00 per 15 ounces Scenario 2 –60-gigabyte MP3 player costs $150 –80-gigabyte model costs $190 Solution: compare items using unit prices Goal: program should find the unit price of an item

40. Alice in Action with Java40 Designing the UnitPricer Program Step 1: elements of user story built around unit price –Query: “What is the price of the first item?” –Read the first price from the keyboard –Query “How many units are in the first item?” –Read the number of units in the first item –Perform the first four actions for the second item –Compute and display the unit prices of the two items –Use of a generic item broadens program’s application Step 2: extract the objects from the noun phrases Step 3: extract the methods from the verb phrases

41. Alice in Action with Java41 Designing the UnitPricer Program (continued)

42. Alice in Action with Java42 Designing the UnitPricer Program (continued)

43. Alice in Action with Java43 Designing the UnitPricer Program (continued) Step 4: develop the UnitPricer algorithm The algorithm is the blueprint for the program Generalization: broadens application of a program Generalization in the UnitPricer algorithm –The use of “item” in place of cereal box and MP3 player –“Item” is a generic term embracing a variety of objects

44. Alice in Action with Java44 Designing the UnitPricer Program (continued)

45. Alice in Action with Java45 Writing the UnitPricer Program A summary of the steps –Create a new Java project in Eclipse –Create the UnitPricer class –Implement the algorithm in main() Figure 7-24 presents the final version

46. Alice in Action with Java46 Writing the UnitPricer Program (continued)

47. Alice in Action with Java47 Testing the UnitPricer Program Conduct testing using easy-to-verify values The printf() message revisited –Begin format-string with %n to advance cursor one line –%w.pf placeholder used to specify width and precision Format-string: "%nItem 1 unit price: $%7.2f“ –%n advances the cursor to the next line –%7.2f : 7 spaces, two decimal places for a real number

48. Alice in Action with Java48 Testing the UnitPricer Program (continued)

49. Alice in Action with Java49 Testing the UnitPricer Program (continued)

50. Alice in Action with Java50 Solving the Problems Solve the MP3 player problem –Reminder: the 60-gigabyte model cost $150 –Reminder: the 80-gigabyte model cost $190 MP3 player solution: 80-GB model is a better value Solve the corn flakes problem –Reminder: the 12-ounce “regular” size cost $2.90 –Reminder: the 15-ounce “economy” size cost $4.00 Corn flakes solution: regular size box is a better value

51. Alice in Action with Java51 Solving the Problems (continued)

52. Alice in Action with Java52 Solving the Problems (continued)

53. Alice in Action with Java53 The Software Engineering Process Six steps are similar for Java and Alice development Software design: Steps 1-4 Software implementation and testing: Steps 5 and 6 Software engineering: –Includes software design, implementation, and testing

54. Alice in Action with Java54 The Software Engineering Process (continued)

55. Alice in Action with Java55 Summary Steps in program development: designing, writing, running, and testing Java: object-oriented language used to develop cross-platform applications Algorithm: sequence of steps that solves a problem IDE: program development tool that bundles an editor, compiler, run-time environment, and debugger Eclipse: free IDE for Java developed by IBM

56. Alice in Action with Java56 Summary (continued) Package: group of related, predefined classes import statement: exposes a program to classes in a package Display values by sending print(), println(), or printf() to an instance of System.out Connect a program to the keyboard using a Scanner object Software engineering: methodology for designing, implementing, and testing software