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

2. Alice in Action with Java2 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

3. Alice in Action with Java3 Writing a First Java Program Integrated development environment (IDE) –Program editor –Compiler –Run-time environment –Debugger Eclipse –Free IDE for various languages developed by IBM –Java programs in this text are built using Eclipse

4. Alice in Action with Java4 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

5. Alice in Action with Java5 Starting Eclipse (continued)

6. Alice in Action with Java6 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

7. Alice in Action with Java7 Writing a Java Program Using Eclipse (continued)

8. Alice in Action with Java8 Writing a Java Program Using Eclipse (continued)

9. Alice in Action with Java9 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

10. Alice in Action with Java10 Writing a Java Program Using Eclipse (continued)

11. Alice in Action with Java11 Writing a Java Program Using Eclipse (continued)

12. Alice in Action with Java12 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

13. Alice in Action with Java13 Compiling a Java Program Using Eclipse (continued)

14. Alice in Action with Java14 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

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

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

17. Alice in Action with Java17 Running a Java Program Using Eclipse (continued)

18. Alice in Action with Java18 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

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

20. Alice in Action with Java20 Java Basics Strategy: compare the first program to the algorithm References –Algorithm developed in Section 7.1 –DollarsToEurosConverter.java in Figure 7-20

21. Alice in Action with Java21 Java Basics (continued)

22. Alice in Action with Java22 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

23. Alice in Action with Java23 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

24. Alice in Action with Java24 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

25. Alice in Action with Java25 The Simplest Java Program (continued)

26. Alice in Action with Java26 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

27. Alice in Action with Java27 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

28. Alice in Action with Java28 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;

29. Alice in Action with Java29 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

30. Alice in Action with Java30 Some Java Statements (continued)

31. Alice in Action with Java31 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

32. Alice in Action with Java32 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

33. Alice in Action with Java33 Designing the UnitPricer Program (continued)

34. Alice in Action with Java34 Designing the UnitPricer Program (continued)

35. Alice in Action with Java35 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

36. Alice in Action with Java36 Designing the UnitPricer Program (continued)

37. Alice in Action with Java37 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

38. Alice in Action with Java38 Writing the UnitPricer Program (continued)

39. Alice in Action with Java39 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

40. Alice in Action with Java40 Testing the UnitPricer Program (continued)

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

42. Alice in Action with Java42 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

43. Alice in Action with Java43 Solving the Problems (continued)

44. Alice in Action with Java44 Solving the Problems (continued)