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BlueJ Lab Page 1 of 6 Introduction to BlueJ The purpose of this lab is to allow you to become more familiar with the BlueJ Integrated Development Environment, (IDE). You should have already briefly used BlueJ in your first lectoral class. Preliminaries Once you are logged on to the system, go to the start menu, then Computing, then Java and then BlueJ. Click on the BlueJ option. This should start the BlueJ. You will see the following window: Figure 1: BlueJ IDE Starting to use BlueJ In the Java world a program under development is known as a project. A Java program will typically consist of several files. The first thing you need to do is to set up your own project. Task 1 In the BlueJ window select “Project”-> “New Project”. (see figure 2) BlueJ Lab Page 2 of 6 Figure 2: You will be presented with a dialog window: Figure 3: Navigate to the location you want to use to for the project. This should be on your U: drive, probably in a folder called CM0047, that you will have created. Once there, enter the name of the project in the file name field. For this exercise we want you to call the project, Shapes. Enter Shapes and press return. You have now created your first project. You have created a folder which contains two files: README.TXT package.bluej The first is a text file that can be used to record notes about the project. The next one belongs to BlueJ. It contain administrative information that is used by BlueJ. You cannot read it. Task 2 The next stage is to create some files. Normally you would do this but for this part of the lab we are going to provide you will some files. You will find these on Blackboard. The files are called: Canvas.java Circle.java Square.java Triangle.java Copy these files into you folder Shapes. Task 3 Select Edit and then select “Add Class from File”. You will be presented with a file selection dialog. Move to the folder Shapes and select the 4 java files. BlueJ Lab Page 3 of 6 Figure 4: You will need to click the Compile button in the BlueJ tool bar. You should now see something similar to this: Figure 5: Task 4 You can now explore this project. 1. Right click on the Square class and choose new Square() 2. Left click on the Square object in the Object Bench You will see a list of the methods available for your use. Select makeVisible(). A small window will appear showing a square in its default position and default colour. 3. Experiment with moveLeft(), moverRight(), moverUp(0, moveDown() ,makeInvisible() and makeVisible(). Task 5 If you invoke moveHorizontal you will see the following dialog: BlueJ Lab Page 4 of 6 Figure 6: You are being asked to enter some data. (You are being asked to provide a value for a parameter.) In this case this will be an integer which equals the number of pixels you want to move the square – a positive number moves it to the right and a negative number to the left. Enter a value in the range 50 to 100. Experiment with the other methods that require an integer parameter. There are four others. Task 6 There is just one method left to use – changeColor( String newColor). Invoke this method and you should see Figure 7: The parameter this time is of type String. We will look at type String in one of the lectorals. For the moment take it to be a sequence of characters inside “ “. The acceptable strings are shown in the dialog box. Type one in. Task 7 Now create some circle and triangle objects and perform similar experiments with them. Task 8 You are going to start a new exercise using the classes in the shapes project and we need to reset the canvas. Go to Tools in the menu bar and select “Reset Java Virtual Machine”. This has the effect of restarting the project. BlueJ Lab Page 5 of 6 Figure 8: Look at the following picture Figure 9: By creating various objects and using their methods build this picture. As you do write down the steps you are taking. These steps are an “algorithm” for producing the picture. Task 9 You are going to carry out some simple editing on a Java class that will, hopefully, draw the picture shown in figure 9. Close your current project and create a new one called Picture2. Add the four java files you used in the Shapes to this new project. (If you have forgotten how, look at Task 3 above). From Blackboard add the file Picture2.java to the project. ( you will need to copy it into the Picture2 folder and then add it to the project). Once you have added it to the project double click on the Picture2 class and select “OpenEditor”. Figure 10: Find the draw method. It contains four sections of code – two for squares, one triangle and a circle. Where ever you see the phrase “ENTER AN INTERGER VALUE” replace it with a suitable integer value and when you see the phrase “ENTER A COLOR STRING” enter a suitable color string, e.g. “red”. BlueJ Lab Page 6 of 6 When you have entered all the necessary integer values and strings click Compile. You will get a message at the bottom of the edit window. Hopefully it will say “Class compiled – no syntax errors”. If it doesn’t say this see if you can understand what the problem is and then ask the lab tutor for help. Once the file has compiled create a picture object and select the draw method for that object. Did you draw the correct picture? Task 10 The final task in this lab is for you to create your own picture using Circle, Square and Triangle objects. In order to do this you must first create a new project. Then add the Square, Circle, Triangle and Canvas classes to the project. On Blackboard you will find a file MyPicture.java copy it and add it to the project. The following is some of the contents of that file: Figure 11: You need to: 1. Plan your picture 2. Open the editor for MyPicture 3. Declare each of the shapes you want to use, (look back at the code in Picture2.java to see the kind of thing you should be entering) 4. Compile a. If you have a syntax error correct it b. If there is no error continue 5. Add the instructions for your first shape 6. Compile a. If you have a syntax error correct it b. If there is no error continue 7. Repeat for all your shapes. When you have finished create a MyPicture object and execute its draw method. public class MyPicture { // declare the shapes you want to use here ....... /** * Draw this picture. */ public void draw() { // Add the instructions for each of your shapes here } CM0718 : Week 01 Exercises These exercises are taken from the BlueJ book. Exercise 1.13 In the source code of class Picture, find the part that actually draws the picture. Change it so that the sun will be blue rather than yellow. Exercise 1.14 Add a second sun to the picture. To do this, pay attention to the field definitions close to the top of the class. You will find this code: private Square wall; private Square window; private Triangle roof; private Circle sun; You need to add a line here for the second sun. For example: private Circle sun2; Then write the appropriate code for creating the second sun. Exercise 1.15 Challenge exercise (This means that this exercise might not be solved quickly. We do not expect everyone to be able to solve this at the moment. If you do – great. If you don’t, then don’t worry. Things will become clearer as you read on. Come back to this exercise later.) Add a sunset to the single-sun version of Picture. That is: make the sun go down slowly. Remember: The circle has a method slowMoveVertical that you can use to do this. Exercise 1.16 Challenge exercise If you added your sunset to the end of the draw method (so that the sun goes down automatically when the picture is drawn), change this now. We now want the sunset in a separate method, so that we can call draw and see the picture with the sun up, and then call sunset (a separate method!) to make the sun go down. Exercise 1.20 Call the numberOfStudents method of that class. What does it do? Exercise 1.21 Look at the signature of the enrollStudent method. You will notice that the type of the expected parameter is Student. Make sure you have two or three students and a LabClass object on the object bench, then call the enrollStudent method of the LabClass object. With the input cursor in the dialog entry field, click on one of the student objects – this enters the name of the student object into the parameter field of the enrollStudent method (Figure 1.8). Click Ok, and you have added the student to the LabClass. Add one or more other students as well. Exercise 1.22 Call the printList method of the LabClass object. You will see a list of all the students in that class printed to the BlueJ terminal window (Figure 1.9). Exercise 1.23 Create three students with the following details: Snow White, student ID: 100234, credits: 24 Lisa Simpson, student ID: 122044, credits: 56 Charlie Brown, student ID: 12003P, credits: 6 Then enter all three into a lab and print a list to the screen. Exercise 1.24 Use the inspector on a LabClass object to discover what fields it has. Exercise 1.25 Set the instructor, room, and time for a lab, and print the list to the terminal window to check that these new details appear. Exercise 1.26 In this chapter we have mentioned the data types int and String. Java has more predefined data types. Find out what they are and what they are used for. To do this, you can check Appendix B, or look it up in another Java book or in an online Java language manual. One such manual is at http://java.sun.com/docs/books/tutorial/java/nutsandbolts/datatypes.html Exercise 1.27 What are the types of the following values? 0 "hello" 101 –1 true "33" 3.1415 Exercise 1.28 What would you have to do to add a new field, for example one called name, to a circle object? Exercise 1.29 Write the signature for a method named send that has one parameter of type String, and does not return a value. Exercise 1.30 Write the signature for a method named average that has two parameters, both of type int, and returns an int value. Exercise 1.31 Look at the book you are reading right now. Is it an object or a class? If it is a class, name some objects. If it is an object, name its class. Exercise 1.32 Can an object have several different classes? Discuss.