Alice in Action with Java

Alice in Action with Java Chapter 7 From Alice to Java

Objectives • Write some first Java programs • Learn the basics of the development process for Java programs • Begin making the transition from Alice to Java Alice in Action with Java

From Alice to Java • 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 Alice in Action with Java

Program Development • The four steps of computer programming • 1. Designing the program • 2. Writing the program • 3. Running the program • 4. Testing the program Alice in Action with Java

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 Alice in Action with Java

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) Alice in Action with Java

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 Alice in Action with Java

The Object List (continued) Alice in Action with Java

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 Alice in Action with Java

The Operations List (continued) Alice in Action with Java

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 Alice in Action with Java

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,Playbutton • We are going to learn to develop programs using command line tools • BlueJ is a simple-to-use IDE for Java Alice in Action with Java

Java Programming Process • Use a text editor to create a file containing the program code • vim MyFirstProgram.java • Compile the program • javac MyFirstProgram • Run the program • java MyFirstProgram Alice in Action with Java

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

DollarsToEurosConverter import java.util.Scanner; /** DollarsToEurosConverter converts dollars to euros @author Joel Adams */ public class DollarsToEurosConverter { public static void main( String [] args) { System.out.print( "How many dollars? "); Scanner keyboard = new Scanner( System.in); double dollars = keyboard.nextDouble(); System.out.print( "How many euros per dollar? "); double eurosPerDollar = keyboard.nextDouble(); double euros = dollars * eurosPerDollar; System.out.printf( "%.2f dollars => %.2f euros\n", dollars, euros); } } Alice in Action with Java

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 Alice in Action with Java

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 class should have an opening comment • Place it just above the "public class …" • In general, add comments to improve readability Alice in Action with Java

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 • However, you cannot replace main with another method Alice in Action with Java

The Simplest Java Program Alice in Action with Java

The main Method • 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 } Alice in Action with Java

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 Alice in Action with Java

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; Alice in Action with Java

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 Alice in Action with Java

Use printf for formatting numbers Alice in Action with Java

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 Alice in Action with Java

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 Alice in Action with Java

Designing the UnitPricer Program (continued) Alice in Action with Java

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 Alice in Action with Java

Designing the UnitPricer Program (continued) Alice in Action with Java

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

Writing the UnitPricer Program (continued) Alice in Action with Java

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“ • %nadvances the cursor to the next line • %7.2f: 7 spaces, two decimal places for a real number Alice in Action with Java

Testing the UnitPricer Program (continued) Alice in Action with Java

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 Alice in Action with Java

Solving the Problems (continued) Alice in Action with Java

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 Alice in Action with Java

The Software Engineering Process (continued) Alice in Action with Java

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 Alice in Action with Java

Summary (continued) • Package: group of related, predefined classes • importstatement: 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 Alice in Action with Java

Alice in Action with Java