Imperative and Object Oriented Programming. Tutorial 1. Charlie Abela Department of Artificial Intelligence

Transcription

1 Imperative and Object Oriented Programming Tutorial 1 Department of Artificial Intelligence charlie.abela@um.edu.mt

2 Tutorial 1 In this tutorial you will be using the BlueJ IDE to develop java classes. BlueJ is a Java development environment specifically designed for teaching at an introductory level. It was designed and implemented by the BlueJ team at Deakin University, Melbourne, Australia, and the University of Kent at Canterbury, UK. 1. Introduction to BlueJ Installation on Windows is a straight forward process. The distribution file is called bluejsetup-xxx.exe, where xxx is a version number. For example, the BlueJ version distribution is named bluejsetup-200.exe. You might get this file on disk, or you can download it from the BlueJ web site at Execute this installer. The installer lets you select a directory to install to. It will also offer the option of installing a shortcut in the start menu and on the desktop. After installation is finished, you will find the program bluej.exe in BlueJ s installation directory. The first time you launch BlueJ, it will search for a Java system (JDK). If it finds more than one suitable Java system (e.g. you have JDK and JDK installed), a dialog will let you select which one to use. If it does not find one, you will be asked to locate it yourself (this can happen when a JDK system has been installed, but the corresponding registry entries have been removed). The BlueJ installer also installs a program called vmselect.exe. Using this program, you can later change which Java version BlueJ uses. Execute vmselect to start BlueJ with a different Java version. The choice of JDK is stored for each BlueJ version. If you have different versions of BlueJ installed, you can use one version of BlueJ with JDK and another BlueJ version with JDK 1.5. Changing the Java version for BlueJ will make this change for all BlueJ installations of the same version for the same user. 1.1 Keep it Simple BlueJ projects, like standard Java packages, are directories containing the files included in a project. After starting BlueJ, use the Project Open... menu command to select and open a project. 1. The window might not look exactly the same on your system, but the differences should be minor. Tutorial 1 Java Tutorials 2

3 Figure 1: BlueJ interface 2. Preferences related to the editor and other options can be set from here Figure 2: BlueJ preference settings 3. To create a new project, select Project New... from the menu. A file selection dialogue opens that lets you specify a name and location for the new project. Try that now. Set the name of the new project to tutorial_1. After you click OK, a directory will be created with the name you specified, and the main window shows the new, empty project. Tutorial 1 Java Tutorials 3

4 4. Lets try out BlueJ by creating a new class in a tutorial_1. Select the New Class... menu item or toolbar button. This is only possible while you have the project open. A dialog will appear to let you enter a name for the new class: You have to enter a name, and choose one of the options Class, Abstract Class, Interface, "Applet", Unit Test or Enum. Figure 3: Creating a new class The name must be a valid Java identifier. In short, it must be a word that consists only of letters, digits and the underscore (_). No spaces or other characters are allowed. The first character may not be a digit. Choose a name such as HelloWorld. Class, Abstract Class, Interface, "Applet", Unit Test or Enum options only determine what kind of skeleton is used for the initial source of the class. It is not a final choice: you could change your mind later, and replace the complete source code of, say, a class with code for an interface. The environment would recognise that the class is now an interface and treat it accordingly. Of course, this works the other way around as well. 5. Once the class has been created, the Editor can be accessed. Figure 4: Editing code Tutorial 1 Java Tutorials 4

5 6. With the creation of each class, some code will automatically be created. This can be edited as required. Figure 5: Using the editor 7. To permanently set the coding preferences, such as brackets style (inline or not), default variable declarations and methods, we can edit BlueJ s underlying templates which are found it the following directory: home\bluej\lib\english\templates\newclass. Each template related to classes, applets etc can be edited separately. 8. Edit the code in the HelloWorld class and enter only the following statements. public class HelloWorld{ public static void main(string[] args){ System.out.println("Hello World"); } } 9. To compile this code, just hit the compile button. This will automatically save and compile the code. If no errors are detected then the message: Class compiled no syntax errors, will be displayed at the bottom of the editor Tutorial 1 Java Tutorials 5

6 Figure 6: Compiling code 10. To execute the Class rt. click and choose void main(string[] args) 11. Figure 7: Executing classes The output can be seen through the Terminal window. If the terminal window does not launch automatically: Click on View, Choose Terminal. Figure 8: Checking Output in Terminal Tutorial 1 Java Tutorials 6

7 12. Appropriate documentation can be generated automatically. A browser window will be launched and the documentation displayed as a web page Figure 9: Generate JavaDoc Figure 10: View Java documentation 2. Introduction to Eclipse The Eclipse Platform is designed for building integrated development environments (IDEs) that can be used to create applications as diverse as web sites, embedded Java programs, C++ programs, and Enterprise JavaBeans. In this tutorial we will show the (very) basic functionality of this program, which is call The Platform when talking about Java Developing Tools. Visit for further information. Tutorial 1 Java Tutorials 7

8 Eclipse is released open source software license, so you can download for free from its website: The most suitable version (for you) at this stage is the Eclipse Classic. Once downloaded, installing Eclipse should be quite straight forward. It is suggested that you install it in the root directory. 2.1 Using Eclipse 1. Launching Eclipse prompts you for workspace location. This is where all your projects will be stored and you can choose a different location every time you start Eclipse or check the Use this as the default option. It is recommended that you set your own workspace folder. Figure 11: Selecting the Workspace 2. If it s the first time that you are running eclipse on your machine, after the workspace is chosen, the following startup screen will be displayed. Figure 12: Startup Screen Tutorial 1 Java Tutorials 8

9 3. Choosing the workbench icon takes you to the Java IDE interface Figure 13: Workbench 4. Eclipse works with a Tab system, it means that each item is displayed in the same place all the time and we can select which Tabs we want to display in each moment. The default view contains: 1. Navigator Tab: This is the place where our projects will be located 2. Java View: The code of our programs as the Visual Editor preview will be displayed here 3. Outline: All the functions and the includes of the code 4. Console: The Java Standard Output will be displayed here 5. Properties Tab: This will become handy when eventually you ll use the Visual Editor. If we click on an item, the properties of this object could be changed by changing the values in this tab 6. Run Button: We can save time by clicking this button instead of going to the menu. The first time that we run a project, Eclipse will prompt for the type and way to run it 7. New: To add new classes, visual classes we can click here instead of clicking on the File Menu 5. Creating a project in Eclipse is quite straight forward. The wizard will help you define all aspects of the new project. Tutorial 1 Java Tutorials 9

10 Figure 14: New Project 6. After choosing to create a new Java Project, then you have to enter the project details and set some other issues. Figure 15: Creating a new Project Tutorial 1 Java Tutorials 10

11 Project name should be entered: enter unit1 Leave the Create new project in workspace checked Check that the correct JVM is used Choose the Create separate source and output folders 7. Check the Allow output folders for source folders. In this way source files will be separate from the class files, giving a better structure to your programs. Figure 16: Program code structure 8. Clicking on Finish will generate the following folder structure. Figure 17: Source/Class folders Tutorial 1 Java Tutorials 11

12 9. Create a new class and name it HelloWorld. Figure 18: Add new class to src folder 10. When asked to enter the class details, create also a package (which will store all the exercises that will be done in relation to the first unit. Name the package: exercises (use small letters) and the class: HelloWorld. Figure 19: New package and class details Tutorial 1 Java Tutorials 12

13 Also check the box for the main method and uncheck the one for inherited abstract methods. Clicking finish will create the class. Figure 20: New class created 11. Add to the main method the following statement and save the file System.out.println( Hello World ); 12. To run your program rt-click on the src file, choose Run As and then click on Java Application. This will execute the program and output the message Hello World onto the Console window. Figure 21: Execute Program Tutorial 1 Java Tutorials 13

14 3. Problems The following coding problems are related to the basics of the java language: topics covered include, variables (declaration and initialisation), constants, data types, numeric type casting, operator precedence and associativity, input from console. 3.1 Problem Set 1. Write a program CalorieCalc.java, that accepts a person s weight and displays the number of calories the person needs in one day. Use the formula: calories = bodyweight * Write a class Pythagoras.java, that reads the lengths of two sides of a right -angled triangle a and b. The program should then calculate and display the length of the hypotenuse, using the formula : h = (a 2 + b 2 ) 3. Write a program, CorrectChange.java, which takes in a purchase price and a tendered amount (both in cents) and then displays the correct values and change in euros, 50 euro cent, 20 euro cent and 10 euro cent coins. Purchase Price: Euro Amount Tendered: Euro Your change: Euro one euro coin(s) 0 50 cent coin(s) 1 20 cent coin(s) 0 10 cent coin(s) 4. A JavaCoffee outlet runs a catalogue business. It sells one type of coffee beans. The company sells the coffee in 2kg bags only and the price of a single bag is Euro When a customer places an order, the company ships the order in a box. The boxes come in three sizes, large (hold 20 bags), medium (hold 10 bags) and small (hold 5 bags). The cost of Tutorial 1 Java Tutorials 14

15 packaging varies according to box size: large (Euro 2), medium (Euro 1.5) and small (Euro 1). E.g. the cost of 52 bags will be shipped in two large, one medium and one small, boxes. Write a program, JavaCoffee.java, that computes the total cost of an order and displays the output as below. Number of bags ordered: 52 Euro 286 Boxes used: 2 large - Euro medium - Euro small - Euro 1.00 Total cost is: Euro % : Euro Total: Euro Write a program, LoanCalculator.java, which calculates both monthly and total payments for a given loan amount, annual interest rate and loan period. The user is expected to enter three values: loanamount, interestrate and loanperiod. The program will compute the monthly and total payments and then outputs the results. See example output below. Amount Rate Loan Monthly Total Write a program, TicketBooth.java, which computes the total ticket sales for a concert. There are three types of seatings: A, B and C. The program accepts the number of tickets sold and the price of a ticket for each of the three types of seats. The total sales are computed and result outputted. 7. Implement a program, Ticket.java. The program should perform the following operations: i. Read from the keyboard the first and the last name of a passenger. ii. Read from the keyboard the names of the departure city and country. iii. Read from the keyboard the names of a destination city and country. Tutorial 1 Java Tutorials 15

16 iv. Display the ticket's full details, including the pricing details of the ticket (assume that one price fits all and that Vat is 18% and taxes are a fixed amount) 8. Write a program, Quadratic.java, that solves quadratic equations. The program will take three values standing for a, b and c, will find the roots of the equation and display them on screen. Use: -b ± (b 2 2a 4ac) 9. Write a program, LeapYear.java, that given a year will return whether it is a leap year or not. Remember that a year is a leap year only if either (i) divisible by 400 or (ii) divisible by 4 but not There are a number of different formats for representing color. RGB format specifies the level of red (R), green (G), and blue (B) on an integer scale from 0 to 255. RGB is the primary format for LCD displays, digital cameras, and web pages. However for publishing books and magazines the primary format used is the CMYK format. This specifies the level of cyan (C), magenta (M), yellow (Y), and black (K) on a real scale of 0.0 to 1.0. Write a program RGBtoCMYK.java that reads in three integers red, green, and blue and prints out equivalent CMYK parameters. The mathematical formulas for converting from RGB to an equivalent CMYK color are: Tutorial 1 Java Tutorials 16