COMP1406 Tutorial 1. Objectives: Getting Started:

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1 COMP1406 Tutorial 1 Objectives: Write, compile and run simple Java programs using the IntelliJ Idea IDE. Practice writing programs that require user input and formatted output. Practice using and creating simple objects. Learn how to submit an assignment in culearn. To practice solving problems that use IF statements, FOR/WHILE loops & the Math class. Getting Started: Here are some helpful reminders about using the Windows machines in the tutorial room. Please take care that you save your data somewhere that is external to the lab computer. In particular, be careful where you save your data while working on the school machines. It is possible that you may lose data on the school computers, because you did not move your data to your Z drive, dropbox, google drive, USB memory stick, it to yourself, etc., before you logged off. The loss of data will not be accepted as an excuse for late or missed assignments. IntelliJ Idea is the IDE (Integrated Development Environment) that will be used for tutorials in COMP1406. It is installed on all of the computers in the tutorial room. IntelliJ Idea is free and is available for MacOSX, Windows and Linux operating systems. You should use it on your home computer or laptop to write all of your programs in this course. You will be saving and zipping the project files to hand in for ALL of your assignments. Instructions for downloading and running IntelliJ on your own computer can be found at the end of this document. You can find the executable file for it by going to the Windows start menu and searching for it. Upon startup, you should see a window something like what is shown here: Once IntelliJ has started, you should see the following. Select "Create New Project" to continue: 1

2 A dialog box will appear. Select Java in the left size panel. Then select the New... button on the top right of the window and select JDK in the pop-up menu that appears: 2

3 Select the latest jdk (at least version 1.8.0) from the C:\Program Files\Java folder [Note: The Java folder is in C:\Program Files, NOT C:\Program Files (x86]. Then press OK: A new window will appear. Just click Next: 3

4 Type in Assignment 0 as the Project name, make sure the project location is saving to the Z: drive and then press Finish: Should be Z:\, not C:\ You should see the main workbench window appear: 4

5 Expand the project by clicking the triangle to the left of the Assignment 0 project. Then click the src folder: From the File menu, select New and then Java Class: 5

6 Enter HelloWorld as the class name: You should see a class template formed as shown here (although the name and data in the comment will differ): 6

7 Type in the whole program as shown here: Right-click on the program panel (i.e., on the panel that contains your code) and select Run 'HelloWorld.main()' from the pop-up menu: 7

8 Your program should now run and the result should appear in the bottom Console pane: 8

9 NOTE: If you get an error that says something along the lines of "Invalid Target Release", you may have to change the compiler settings. Go to the File menu and select Settings... then under the Build,Execution,Deployment heading, select Compiler and then Java Compiler. Make sure that it is set to the same Project bytecode version of 1.8 to match the jdk that we set earlier. Click Apply and then Close the window and try running the code again. Tutorial Problems: 1) Create a class called TaxProgram (right click on the src folder in IntelliJ and select New->Java Class) with the code shown below. It should compile and run. Currently, the program just asks the user for his/her taxable income and then the number of dependents that they have. import java.util.scanner; public class TaxProgram { public static void main(string args[]) { double income, fedtax, provtax; int dependents; System.out.print("Please enter your taxable income: "); income = new Scanner(System.in).nextDouble(); System.out.print("Please enter your number of dependents: "); dependents = new Scanner(System.in).nextInt(); fedtax = 0.0; provtax = 0.0; // Add code here Making use of the income and fedtax variables in the code, insert code at the end of the program so that it computes and displays the fedtax using the rules shown below: If the income is less than $29,590, the federal tax should be 17% of the income If the income is in the range from $29, to $59, then the federal tax should be:(17% of $29,590 + (26% of (the income minus $29,590)) If the income is $59,180 or more then the federal tax should be: (17% of $29,590) + (26% of $29,590) + (29% of (the income minus $59,180)) Test your code with the following values to make sure that it is correct before you continue: Income $25,000 $53,000 $65,000 FedTax $4,250 $11, $14,

10 Insert code at the end of the program so that it computes and displays the provincial tax and finally the total tax using the rules shown below: The base provincial tax will be: 42.5% of the federal tax The deductions for the provincial tax will be: $ $328 per dependent The provtax is then calculated $0 if the bas provincial tax is less than the deductions, otherwise as follows: base - deductions The total tax is the sum of the fedtax and the provtax. Test your code with the following values to make sure that it is correct: Income $25,000 $53,000 $65,000 Dependants FedTax $4,250 $11, $14, ProvTax $1, $3, $4, TotalTax $5, $15, $19, ) Adjust your code above so that it displays with the following output format by using System.out.println() statements as well as String.format(): Please enter your taxable income: Please enter your number of dependents: 1 Here is your tax breakdown: Income $25, Dependants Federal Tax $4, Provincial Tax $1, ============================ Total Tax $5,

11 3) Create the following class called ObjectTestProgram (cut/paste the code) which creates 3 objects and displays them: public class ObjectTestProgram { public static void main(string args[]) { String s; Date d; Color c; s = "Hello World"; d = new Date(); c = Color.RED; System.out.println(s); System.out.println(d); System.out.println(c); The code does not compile... JAVA gives a few errors: Error:(6, 9) java: cannot find symbol symbol: class Date location: class ObjectTestProgram Error:(7, 9) java: cannot find symbol symbol: class Color location: class ObjectTestProgram This is JAVA's way of telling you that it does not know where the Date and Color objects are. You have to "tell" JAVA where they are by using an import statement. One way to do this is to add the appropriate import statement to the top of your program. Add the following to the top of your code, and you should notice that Date objects are now recognized in your code and so no compile error will occur on those lines anymore. import java.util.date; Alternatively, instead of trying to remember the import statement, you can have IntelliJ write the import statement for you. For example, click on one of the Color words in your code and then press ALT-ENTER (I'm not sure what keys are to be pressed for a ios or Linux). You will see the following dialog box appear: This lets you choose which class to import. As it turns out, there are three different Color classes defined in JAVA and they appear in three different folders. Select the middle one shown above (since we will use JavaFX later). You will notice that the import statement is added to the top of your program and that the code will now compile and run. Note that we do not need to import the String class since it is part of the "automatically imported" java.lang package. Now the code should compile. Notice the output. Was it as you expected? 11

12 4) Now let us create our own object. Create a class called MyObjectTestProgram: To do this, select the src folder in the left pane and create a new Java Class called MyObjectTestProgram from the menu options by following the File/New/Java Class menu sequence. You should see the following appear (with your name and a different date though): /** * Created by Mark Lanthier on 5/5/2016. */ public class MyObjectTestProgram { Replace the code above with the following code (cut and paste it, to save time): public class MyObjectTestProgram { public static void main(string args[]) { MyObject x; System.out.println(x); Compile the code by right clicking on your code and selecting Compile '...ecttestprogram.java' from the pop-up menu. Note: If you get an error such as this: " Error: java: invalid target release 1.9"... you will have to make a change to your project settings. To do this, select Settings... from the File menu. The select Java Compiler under the Build,Execution,Deployment submenu in the left pane. Select 1.8 as the Project bytecode version and press OK. You should see this error: Error:(3, 9) java: cannot find symbol symbol: class MyObject location: class MyObjectTestProgram You will notice in your code that the word MyObject is in red, indicating that there is an error. The Java compiler is indicating that it has no idea what a MyObject object actually is and we are trying to "use" such an object in this program. We fix this by creating a MyObject class. Create a new Java Class called MyObject. The code for the MyObject class should simply be: public class MyObject { Compile the MyObject class. Congratulations! You have just defined your first object. Now let's see if you can use it. Go back and compile the MyObjectTestProgram. Now JAVA will understand that you want to use the MyObject object that you just defined (it knows this because a MyObject class has been compiled in the same directory). However, the code will still not compile because it generates the error: "variable x might not have been initialized". You will also notice that the x is underlined with a red wavy line in your code. Putting the mouse cursor over this line will tell you the error: 12

13 This is JAVA's "annoying" way of telling you that you did not give a value to variable x. Insert the following line of code between the variable's declaration and the System.out.println line... and then recompile: x = null; The code should now compile. Run the code (i.e., right click on the code and select Run 'MyObjectTestPr...main().java' from the pop-up menu. After you run it once, you will be able to run the program by using the green "play" button at the top right of the IntelliJ toolbar: When the program runs, you should see null displayed. null is JAVA's way of representing an undefined object. You see, even though we created a new MyObject variable x, we did not make a new MyObject object. We only made the variable to hold one. Change x = null; into x = new MyObject(); and then recompile and run your code. You should now see something like this displayed MyObject@140e19d (although the exact numbers and letters may vary). Congratulations! Now you have just created the first instance of your object. Make sure that you notice the difference between defining an object (as we did with MyObject x;) and creating an instance of our object (as we did with x = new MyObject();). Our MyObject object is very plain. You cannot do much with it at the moment. We can only make a bunch of MyObject objects and display them. Try changing your code to look like this: public class MyObjectTestProgram { public static void main(string args[]) { MyObject x1, x2, x3; x1 = new MyObject(); x2 = new MyObject(); x3 = new MyObject(); System.out.println(x1); System.out.println(x2); System.out.println(x3); 13

14 Run the code. Three MyObject objects are created, but all look different when displayed because the weird numbers/letters represent the location of the object in the computer's memory and since each object is a unique one, it is in a different location. Submit Your Work: Before we go any further, let's make sure that you can submit your work. We will create a zip file called Assignment 0.zip that contains all of the java files you wrote so far in this tutorial. Files included will include: HelloWorld.java, TaxProgram.java, ObjectTestProgram.java, MyObjectTestProgram.java and MyObject.java. NOTE THAT ALL SUBMITTED ASSIGNMENTS MUST BE ZIPPED (i.e.,.zip) PROJECT FILES. YOU WILL LOSE MARKS IF YOU ATTEMPT TO USE ANY OTHER COMPRESSION FORMATS SUCH AS.RAR,.ARC,.TGZ,.JAR,.PKG,.PZIP, etc... To do this, go to the folder that contains all of your files. The easiest way to do this is to right click on the src folder within the IntelliJ project and then select Show in Explorer from the menu that appears: A window will then come up showing you the folder that contains your source code. In fact, it will be the Assignment 0 project folder as shown on the next page: 14

15 You will need to expand the directory structure on the left side of the window by continually clicking on the > arrows for the highlighted folders until you click on Assignment 0, as shown above. We will actually zip the entire project folder. Right-click on the Assignment 0 folder in the left pane of the window and select Send to and then Compressed (zipped) folder as shown in the picture on the next page: 15

16 You will see the zipped file shown on the left pane: 16

17 This Assignment 0.zip file is what you will submit. Go to the COMP1406 page in culearn. You will find a submit Assignment 0 option in the assignments section. Clicking this will bring you to a page where you can upload your submission. If you want to load that project into IntelliJ on another computer, you will need to unzip that file on that new computer. Wherever you placed the zip file on your new computer, select it and unzip it by selecting the file and then right-clicking and selecting Extract All... from the popup menu: From the dialog box that appears, click Extract. It should by default, extract to the same folder that contains the zipped file: 17

18 To open the project in IntelliJ, select Open... from the File menu. Select the Assignment 0 folder that is inside of the Assignment 0 folder that you unzipped. MAKE SURE THAT YOU SELECT THE ONE INSIDE OF THE OTHER ONE as shown in the image on the next page: 18

19 The project should be loaded along with all of its original source files. The TAs will follow these steps in order to download and open your project code. MORE CHALLENGING QUESTIONS: 5) Consider the following program that asks the user for a series of exam marks and then computes the average. Create/Save/Compile and Run the program to make sure that it works: import java.util.scanner; public class ForLoopTestProgram { public static void main(string args[]) { int nums, sum; System.out.println("How many exam marks do you want to average? "); nums = new Scanner(System.in).nextInt(); sum = 0; // Get the numbers one at a time, and add them for (int count=1; count<=nums; count++) { 19

20 System.out.println("Enter exam mark " + count + ": "); sum += new Scanner(System.in).nextInt(); System.out.println("The average is " + (sum / nums)); You should get an answer of 59 if you entered 3 exam marks of 66, 25 and 87. Using another FOR loop, add any necessary code inside the existing FOR loop's body so that it displays the entered value followed by a space character and then a series of asterisks (i.e., *) for each value entered. There should be the same number of asterisks as the mark on the exam. Each mark should display on its own line. The result should be a kind of sideways bar graph as shown below. The results below should be produced if you entered 5 exam marks of 66, 25, 87, 91 and 15: 66 ****************************************************************** 25 ************************* 87 *************************************************************************************** 91 ******************************************************************************************* 15 *************** The average is 56 6) Copy your solution code above into a new class called WhileLoopTestProgram then Save/Compile and Run the code to make sure that it still works. Modify the code so that it no longer asks the user for the number of marks beforehand. Instead, it should use a WHILE loop to keep asking for marks until the user enters no mark (i.e., just presses the Enter key, leaving the option pane blank). You may have to alter some variables and add an if statement. Feel free to make any changes that you need. Make sure that it still computes the average correctly. 7) Write a program that takes a point object (x,y) to represent a robot's initial location (in centimeters) as well as its orientation (an angle called theta which is an integer value between 0 and 360 degrees). You can either set these values in your code directly or ask the user for them (using the Scanner class). They should all be integers. Assume the robot moves forward d centimeters. Compute and display the final location of the robot after it moves. The new location is computed as point (x + d cos(theta), y + d sin(theta)). Remember that the sine and cosine functions in JAVA use radians, not degrees. To convert degrees to radians, you need to multiply the degrees by Math.PI/180 and if you need to convert from radians to degrees you can multiply the radians by 180/Math.PI. Test your code...remembering that 0 degrees is to the right (as shown below in red), 90 degrees is up, 180 degrees is left and the angle theta shown below is around 135 degrees. 20