Finally, you get a very easy, user-friendly tool to create and run Java applets. This is what you will use for the rest of the labs.

Transcription

1 Lab 3: Calculator Lab Summary: Getting started with Eclipse Finally, you get a very easy, user-friendly tool to create and run Java applets. This is what you will use for the rest of the labs. More of Java Applets Building on what you learnt to implement in last week s lab, you will make a slightly different, slightly complicated Calculator applet. You will put this in your cps1 folder and it should be accessible from the Internet. In the 1st part of this lab, you will run a simple applet already written for you. This applet will be in your lab3a folder in your cps1 folder. The 2 nd part will be the actual Calculator Applet which will be your lab3b. Your calculator will have two registers visible on the webpage, one called Reg and other called Accum (standing for "register" and "accumulator").both these fields will be DoubleFields. Then you will have 4 Buttons that do the following jobs: set Reg to zero, set Accum to zero, add Reg to Accum and leave the result in Accum and raise Accum to the power Reg and leave result in Accum. NOTE: A Double-field is not a standard Java object/class, like (say) TextField. Thus, to use DoubleField, you would have needed to create this data structure and define its behavior. This is already done for you by some good computer scientist and bundled up nicely in a JAR file which you can import into your project. (JAR= Java ARchive). More details to follow. Getting started with Eclipse: 1. Start (or Launch) Eclipse by: Start -> Programs -> Eclipse -> Eclipse. 2. Eclipse will start and you should see Welcome to Ambient 1.0 in the window. Close this welcome note (by clicking on the X next to Welcome at the top left of the window), you do not need to make any changes/verifications it suggests. 3. You have to first create a new Java Project. 4. This is done by: File (on top left corner) -> New -> Project. 5. A new window wills pop-up with the title New Project. 6. Select (of the many options) Java Project. Then click Next > 7. On clicking Next the next window will ask for the Project Name. 8. Name the project as lab3a. (Note that lab3a is all lower-case). And hit enter (or click Finish). Siddhesh Sarvankar (siddhesh@cs.duke.edu) Page 1 of 5

2 9. This will show a progress bar on the smaller window and after it disappears, you will get a window asking if you want to switch to Java perspective. Click on Yes. The project lab3a will appear in the Package Explorer on the top-left of the screen. You have successfully created a Project in your Workspace called lab3a. Don t be alarmed if you didn t understand this sentence. For the time being, consider it some technical jargon Comp Science people use to sound cool! If you click on the tiny (+) sign next to your lab3a project, you will see a JRE Systems Library under it (actually, inside your Project lab3a). Click on the tiny (+) sign next to JRE Systems Library will show you a whole list of JAR files your Project will be allowed access to. You don t need all those JAR files, but they are what make Java so great. For example, the sunjce_provider.jar, (Sun Java Cryptographic Extension _ Provider) will give your applet the ability to use complex security/cryptographic functionalities which can be used to encrypt/decrypt data and a hoard of Security features. Hence, you, the programmer, don t have to write everything from scratch. 10. You will need to use the awb.jar file in your applet. This is available on the course webpage, Download this file on to a convenient location on your local, Old Chem, machine, preferably on the Desktop. 11. Going to the Eclipse window, Right-click on the lab3a project and, from the menu which appears, select Import. 12. A new window will appear, titled Import, asking you to select an import source. Select Zip file and click Next. 13. The next window will ask you the location of the zip file. In the From zip file line, click on Browse and go to the Desktop (or to the location of ModelAwb.jar file), select that file and click Open. A list of files will appear in the window below the From zip file line. If the Into folder: text field at the bottom half of the window says, lab3a, just click Finish. You will now get a Question asking if you wish to overwrite the.classpath in the folder lab3a. Click on Yes To All. ( Yes to All is only when you are doing this for the 1 st time. Refer the last section, Wrapping up, for instructions while importing this jar file the 2 nd time.) 14. You should see a progress bar and then the window disappears. You will see a few more folders inside your lab3a folder now, ((default package) and awb). Clicking on the tiny (+) better described as expanding the awb directory, you will see Java files called DoubleField.java, IntField.java and StringField.java which are already written for you. 15. In the Default Package, you will see a Model.java file which is a fully functional Java applet, which you should run to get a hang of running applets in Eclipse. 16. Double clicking on Model.java will show you the code in the center window. This is the Eclipse s text editor, analogous to the windows text editor Notepad. As you know, the executable code in Java is not the.java file but the.class file. The list of.java files in the lab3a project/folder should tell you that the java code has not Siddhesh Sarvankar (siddhesh@cs.duke.edu) Page 2 of 5

3 been compiled for you. The process of compiling a whole bunch of small programs (sometimes required to be compiled in a specific sequence) is called Building the project (or Making the project). You will have to Build your lab3a project before you can run it. 17. To Build your lab3a project, click on Project (on top of your screen). In the menu below, you will see that Build Automatically is selected. (If not, you will see Build Project option, which otherwise will be not be available). Build Automatically implies that when you run your code, your Project will be automatically Built. 18. To Run your project, click on Run and from the menu below select Run As -> Java Applet. 19. Your project will be automatically built and you will see an Applet Viewer window on you screen. Use your mouse to adjust the size of this window so that you can see all the Text Fields and buttons on the applet clearly. The Model.java applet is a very simple Divide-by-four program. If you examine he code, you will realize that this applet takes input from the Double Field and outputs its quarter in the 2 nd Text field. A look at the actual java code will help you develop your Calculator. 20. Check to see if this Model.java applet is working properly. Finally, you should make this applet available on your website. This is incredibly simple when using Eclipse. 21. In your lab3a project, (In the Project Explorer) you should also see the index.html file. Double clicking this file will open it in the default program used for html pages, namely your browser. This html file already has the necessary applet code in it and you should be able to run your Model.java applet via this browser. 22. This is still all local to your workspace and not on the Internet. To do this, you need to, some more jargon, Export this project from your workspace to your file system. (For the CS inclined, Eclipse has all these projects stored in workspaces specific to Eclipse. Due to the way Eclipse is set up in your Old Chem machines, your workspace is on this remote, AFSDocs webspace which is named H-drive. You can browse to H-drive via Windows Explorer to find the files you are using in your Eclipse Projects. Your file system is what you see only through Windows OS.) 23. To export this lab3a project, right-click on the lab3a folder/project in the Project Explorer, select Export. 24. This will open a window asking for an Export Destination. Select File System and click Next. 25. You should now see a window titled Export asking for a Destination directory. You want to export everything in the lab3a folder/project. So in the list of files, lab3a (folder) and all files in it should be selected.lab3a will be in the left half of the window which opens and it s contents will be in the right half of the window. Siddhesh Sarvankar (siddhesh@cs.duke.edu) Page 3 of 5

4 If lab3a is the only OPEN project in your Eclipse, then you will have only lab3a and its contents in the lists. 26. You have to select a destination directory. To do this, hit the Browse button, and go to your P drive and into your public_html folder and inside you cps1 folder. (My Computer -> xyz99 on Afs\acpub\users\x\y\ P: ->public_html -> cps1) 27. The To Directory field in your window should now say P:\public_html\cps1. (You could, now onward, just type out the destination directory directly as P:\public_html\cps1 ) 28. Now hit Finish! You will see a Progress bar and the window will disappear. 29. You will now have a lab3a folder inside your public_html/cps1 directory. In this lab3a folder, you will have the index.html file which will run your applet. 30. Check if everything is working! First click on index.html file you see in your P:\public_html\cps1\lab3a\ directory. Then check if it works over the Internet. Open a browser window and enter the URL in the address bar: (Replace xyz99 with your Duke id. And do maintain the same spelling and case in all your file names) Your applet should work on the internet too. Wait! That was not your applet. You have just run Model.java which was given to you. You should now create a lab3b project and follow the exact same process to make your calculator applet. You might want to close the previous lab3a project. To do this, right-click on the lab3a folder/project in the project explorer in the Eclipse window and select Close Project. General steps for the Calculator will be the same. First you create a new Project called lab3b and then import into it the same ModelAwb.jar file. You will have to use the text Editor to modify the java code inside the Model.java file and replace the code with your code. Let all the file names remain the same. This will make all our lives easier! Repeating from before, the Calculator will have the following: Two DoubleFields (one called accum, other reg,) FOUR Buttons: o Set reg to ZERO. o Set accum to ZERO. o Add contents of reg to accum and give result in accum. o Raise accum to the reg th power, and give results in accum. You may, for convenience, also add a few TextFields describing what the applet does and what the two DoubleFields stand for. You must have already written the Exponentiation machine code as a part of your Prelab. If you are not sure whether you are right, here is a brief explanation. As all of you might know, an exponentiation operation, say (x)pow(y) is basically, multiplying x with itself y times. So you need to do something (i.e. x * x) repeatedly, y number of time. This should tell you, you need to use a loop which runs y times. Also, Siddhesh Sarvankar (siddhesh@cs.duke.edu) Page 4 of 5

5 you need to be sure you are using the original value of x (in our example) while multiplying it with the result of the previous loop-run (i.e. previous multiplication). Use temporary integer variables to get values from the DoubleFields and put the final values back into the correct field, accum. Finally when you have typed out the code and built the project and run it using Applet Viewer (Run -> Run As -> Java Applet) and have confirmed that everything is working fine, you have to export this lab3b project to your file system i.e. P:\public_html\cps1 in the exact same way as before. This will create a lab3b folder in your P:\public_html\cps1 folder with the necessary index.html, Model.class and awb.jar file all inside it. To run this final Calculator applet, the URL path will be Wrapping up: If you don t complete this lab NOW, please make sure you have saved all the right files in the P: drive. Files on your desktop, including the ModelAwb.jar file will NOT be permanent. When you do work on the project again, save this ModelAwb.jar file from the course webpage and import it again into the same Project (either lab3a or lab3b). You will get some message asking if you want to overwrite the existing files, DO NOT CLICK ON YES TO ALL, make sure your code, namely Model.java is NOT overwritten. Individually select the files to be overwritten, which can be everything other than Model.java. The most common errors are, believe me, TYPOS! (Especially since Java is casesensitive.) The other common things you may forget are: add ing the buttons and Fields to the applet, adding ActionListener to the buttons. Check for these before asking your TA for help. (One un-common mistake is forgetting to recompile (rebuild) your code EVERYTIME you make a change in the source-code (i.e. DOTjava file). You may not have to worry about this if you have set the Build Automatically option in Eclipse) Siddhesh Sarvankar (siddhesh@cs.duke.edu) Page 5 of 5