Workshop: Lab 1 Engineering Software 1. Lab 1: Introduction to Java Programming Language and Java Development Kit (JDK)

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1 Lab 1: Introduction to Java Programming Language and Java Development Kit (JDK) Learning Objectives 1. To become familiar with Java Environment 2. To become familiar with Java installation 3. To be able to create, edit, compile and run Java programs 4. To learn how to set the PATH environment variable to indicate where the JDK s tools are installed. Lab Work General Note: Study every exercise and for each of them draw a structure diagram. Type in all these programs and run them inside your Java development kit. In your log-book take note of all the results from the execution of these programs and write down any problems that you had to solve. For each program of the exercises, explain clearly what each section of the program is doing. You may need to perform a walk-through, line by line, where this is appropriate. Record all your explanations in the log-book. Remember to put a date in your log-book and also to offer some discussions and a brief conclusion after every week s work. Finally, complete the programming assignments at the end of the exercises, then enter comments in your logbook as you are doing this and save to your floppy disk/cd for submission with your logbook. Part A: Introduction to Java The Java programming language is a general-purpose object-oriented concurrent language. Its syntax is similar to C and C++, but it omits many of the features that make C and C++ complex, confusing, and unsafe. The Java platform was initially developed to address the problems of building software for networked consumer devices. It was designed to support multiple host architectures and to allow secure delivery of software components. To meet these requirements, compiled code had to survive transport across networks, operate on any client, and assure the client that it was safe to run. The popularization of the World Wide Web made these attributes much more interesting. The Internet demonstrated how media-rich content could be made accessible in simple ways. Web browsers such as Mosaic enabled millions of people to roam the Net and made Web surfing part of popular culture. At last there was a medium where what you saw and heard was essentially the same whether you were using a Mac, PC, or UNIX machine, and whether you were connected to a high-speed network or a slow modem. Web enthusiasts soon discovered that the content supported by the Web's HTML document format was too limited. HTML extensions, such as forms, only highlighted those limitations, while making it clear that no browser could include all the features users wanted. Extensibility was the answer. Stavros Dimitriou London South Bank University 1

2 Sun's HotJava browser showcases the interesting properties of the Java programming language and platform by making it possible to embed programs inside HTML pages. These programs are transparently downloaded into the HotJava browser along with the HTML pages in which they appear. Before being accepted by the browser, the programs are carefully checked to make sure they are safe. Like HTML pages, compiled programs are network - and host-independent. The programs behave the same way regardless of where they come from or what kind of machine they are being loaded into and run on. A Web browser incorporating the Java or Java 2 platform is no longer limited to a predetermined set of capabilities. Visitors to Web pages incorporating dynamic content can be assured that their machines cannot be damaged by that content. Programmers can write a program once, and it will run on any machine supplying a Java or Java 2 runtime environment. The Java virtual machine is the cornerstone of the Java and Java 2 platforms. It is the component of the technology responsible for its hardware- and operating systemindependence, the small size of its compiled code, and its ability to protect users from malicious programs. The Java virtual machine is an abstract computing machine. Like a real computing machine, it has an instruction set and manipulates various memory areas at run time. It is reasonably common to implement a programming language using a virtual machine; the best-known virtual machine may be the P-Code machine of UCSD Pascal. The first prototype implementation of the Java virtual machine, done at Sun Microsystems, Inc., emulated the Java virtual machine instruction set in software hosted by a handheld device that resembled a contemporary Personal Digital Assistant (PDA). Sun's current Java virtual machine implementations, components of its Java TM 2 SDK and Java TM 2 Runtime Environment products, emulate the Java virtual machine on Win32 and Solaris hosts in much more sophisticated ways. However, the Java virtual machine does not assume any particular implementation technology, host hardware, or host operating system. It is not inherently interpreted, but can just as well be implemented by compiling its instruction set to that of a silicon CPU. It may also be implemented in microcode or directly in silicon. The Java virtual machine knows nothing of the Java programming language, only of a particular binary format, the class file format. A class file contains Java virtual machine instructions (or bytecodes) and a symbol table, as well as other ancillary information. For the sake of security, the Java virtual machine imposes strong format and structural constraints on the code in a class file. However, any language with functionality that can be expressed in terms of a valid class file can be hosted by the Java virtual machine. Attracted by a generally available, machine-independent platform, implementors of other languages are turning to the Java virtual machine as a delivery vehicle for their languages. Java Platform, Standard Edition (J2SE) provides a complete environment for applications development on desktops and servers and for deployment in embedded environments. It provides the basis for security, database connectivity and more. There are two principal products in the J2SE platform family: J2SE Runtime Environment (JRE) and J2SE Development Kit (JDK). The JRE provides the Java APIs, Java virtual machine, and other components necessary to run applets and applications written in the Java Stavros Dimitriou London South Bank University 2

3 programming language. It is also the foundation for the technologies in the Java 2 Platform, Enterprise Edition (J2EE) for enterprise software development and deployment. The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications. The JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applets and applications. This conceptual diagram illustrates all the component technologies in J2SE platform and how they fit together. J2SE 5.0 Installation notes Installation notes for the J2SE Development Kit 5.0 (JDK), including system requirements and installation instructions, are available for the Microsoft Windows platform. J2SE Development Kit 5.0 (JDK 5.0) is supported on Microsoft Windows running Intel IA32, 100% compatible processors, and AMD Opteron 32. The minimum physical RAM is required to run graphically based applications. More RAM is recommended for applets running within a browser using the Java Plug-in. Running with less memory may cause disk swapping which has a severe effect on performance. Very large programs may require more RAM for adequate performance. Note - The JDK has two version numbers -- external version number 5.0 and internal version number Note - Trying to install the JDK on a non-supported version of Microsoft Windows or on a machine that doesn't have a sufficiently up-to-date Service Pack will cause the installer to generate this warning: "We recommend that you do not install this Java platform for the following reasons: This Java platform does not support the operating system or operating-system service pack on this machine." Stavros Dimitriou London South Bank University 3

4 The Java 2 Platform Standard Edition J2SE Development Kit (JDK) - can be downloaded from the web site. J2SE 5.0 Installation Instructions System Requirements J2SE Development Kit 5.0 (JDK 5.0) is supported on Microsoft Windows running Intel IA32, 100% compatible processors, and AMD Opteron 32. The minimum physical RAM is required to run graphically based applications. More RAM is recommended for applets running within a browser using the Java Plug-in. Running with less memory may cause disk swapping, which has a severe effect on performance. Very large programs may require more RAM for adequate performance. The Java 2 SDK can be installed on the following versions of Windows: Windows XP (with Service Pack 2) Windows XP Home Windows 2000 Professional (with Service Pack 4) Windows 98 (1st and 2nd Editions) Windows ME Windows Server 2003, Web Edition Windows Server 2003, Standard Edition Windows Server 2003, Enterprise Edition Windows Server 2003, DataCenter Edition Note: Trying to install the JDK on a non-supported version of Microsoft Windows or on a machine that doesn't have a sufficiently up-to-date Service Pack will cause the installer to generate this warning: "We recommend that you do not install this Java Platform for the following reasons: This Java Platform does not support the operating system or operating-system service pack on this machine." In this procedure, you will run the self-installing executable to unpack and install the JDK software bundle. As part of the JDK, this installation includes the Java Plug-in and Java Web Start, as well as an option to include the public Java 2 Runtime Environment. (The JDK also contains a private JRE for use only by its tools.). For example, if you are downloading the installer for update 1.5.0_05, the following file name: jdk- 1_5_0_<version>-windows-i586.exe would become: jdk-1_5_0_05-windowsi586.exe If you save the self-installing executable to disk without running it from the download page at the web site, notice that its byte size is provided on the download page. Once the download has completed, check that you have downloaded the full, uncorrupted software file. Note - (1) You must have administrative permissions in order to install the JDK on Microsoft Windows 2000 and XP. (2) For users doing this installation on non-western 32-bit machines, select "Custom" for Setup Type. Then, in Custom Setup under feature 2 ("Support for Additional Languages"), select "This feature will be installed on local hard drive." Stavros Dimitriou London South Bank University 4

5 The file jdk-1_5_0_<version>-windows-i586-i.exe is the JDK installer. If you downloaded it instead of running it directly from the web site, double-click on the installer's icon. Then follow the instructions the installer provides. The installer may ask you to reboot your computer. When done with the installation, you can delete the download file to recover disk space. Installed Directory Tree The JDK has the directory structure shown below. jdk1.5.0_<version> bin lib demo LICENSE jre COPYRIGHT README.txt include readme.html bin lib In addition, the Java Plug-in and Java Web Start will automatically be installed. Look for a Java Web Start icon on your desktop. There will also be an entry for Java Web Start in the Start -> Programs menu. Java Web Start -- Compatibility: The release of Java Web Start that comes with this JDK/JRE can be run on JDK/JRE or later. It will not work with JDK/JRE 1.1.x or earlier. Upgrading from Previous Versions: If you have a previous release of Java Web Start, do not uninstall it. Uninstalling it will cause the download cache to be cleared, and all previously installed Java Web Start application data will have to be downloaded again. This new release will overwrite previous installations and automatically update browsers to use this new release. The configuration files and program files folder used by Java Web Start have changed, but all your settings will remain intact after the upgrade, since Java Web Start will translate your settings to the new form. Uninstalling JDK/JRE 5.0: (1) The only way to uninstall Java Web Start is to uninstall JDK/JRE 5.0. But note that doing so will remove the Java Web Start cache, which stores the Java Web Start application data. Uninstalling the JDK/JRE will not, however, remove the cache for previous releases of Java Web Start (1.0.1 and 1.2). Previous releases have separate uninstallers for Java Web Start. (2) You may see a misleading message if you do the following: first download and cache a Java Web Start (JNLP) application with JDK/JRE 5.x; next remove JDK/JRE 5.x using "Add or Remove Programs" from the Windows Control Panel; then try to remove the Java Web Start application using "Add or Remove Programs." This misleading message can occur as follows: When you select to remove the application, you will see an "Uninstaller Error" dialog saying "An error occurred while trying to remove Java- Application: <name> App. It may have already been uninstalled. Would you like to remove Java-Application: <name> App from the Add or Remove program list?" If you say yes to this, then you will see another "Uninstaller Error" dialog saying "You do not have sufficient access to remove Java-Application: <name> App from the Add or Remove Program list. Please contact your system administrator." This is the misleading message. It implies that the problem is due to privileges. It is not. The problem is that you have already removed the Java Web Start application when you removed JDK/JRE 5.x, but this is not reflected in the "Add or Remove Programs" dialog until it is refreshed by pressing F5 or it is closed and reopened. To avoid seeing this misleading message, either press F5 or close and reopen the dialog. Any Java Web Start application that was downloaded and cached with JDK/JRE 5.x will no longer appear in the list of currently installed programs. Using Java Web Start with Netscape 6.x/7.x: For Netscape 6.x/7.x users, setup the Java Web Start MIME type (JNLP) in the Edit->Preferences->Navigator->Helper Stavros Dimitriou London South Bank University 5

6 Applications section. The file extension is jnlp; MIME Type is application/x-javajnlp-file. It should be handled by the javaws executable file in your Java Web Start directory. Also note that, due to a problem with the JavaScript in Netscape 6.x/7.x, you must use the non-javascript version of the demos page. Update the PATH variable You can run the JDK without setting the PATH variable, or you can optionally set it as a convenience. Should I set the PATH variable? Set the PATH variable if you want to be able to conveniently run the JDK executables (javac.exe, java.exe, javadoc.exe, etc.) from any directory without having to type the full path of the command. If you don't set the PATH variable, you need to specify the full path to the executable every time you run it, such as: C:> "\Program Files\Java\jdk1.5.0_<version>\bin\javac" MyClass.java It's useful to set the PATH permanently so it will persist after rebooting. How do I set the PATH permanently? To set the PATH permanently, add the full path of the jdk1.5.0_<version>\bin directory to the PATH variable. Typically this full path looks something like C:\Program Files\Java\jdk1.5.0_<version>\bin. Set the PATH as follows, according to whether you are on Microsoft Windows NT or 98/2000/ME. Microsoft Windows NT, 2000, and XP - To set the PATH permanently: a. Choose Start, Settings, Control Panel, and double-click System. On Microsoft Windows NT, select the Environment tab; on Microsoft Windows 2000 select the Advanced tab and then Environment Variables. Look for "Path" in the User Variables and System Variables. If you're not sure where to add the path, add it to the right end of the "Path" in the User Variables. A typical value for PATH is: b. C:\Program Files\Java\jdk1.5.0_<version>\bin Capitalization doesn't matter. Click "Set", "OK" or "Apply". The PATH can be a series of directories separated by semi-colons (;). Microsoft Windows looks for programs in the PATH directories in order, from left to right. You should only have one bin directory for a JDK in the path at a time (those following the first are ignored), so if one is already present, you can update it to jdk1.5.0_<version>\bin. c. The new path takes effect in each new Command Prompt window you open after setting the PATH variable. Uninstalling the JDK If you should ever want to uninstall the JDK, use the "Add/Remove Programs" utility in the Microsoft Windows Control Panel. As an alternative method, if you still have the original installation program that you used to install the JDK, you can double click on it to launch an uninstall program. Stavros Dimitriou London South Bank University 6

7 Part B: Installing the latest version of the J2SE Development Kit (JDK) (This is an exercise to help you on how to install JDK at your own PC) 1. Follow the procedure above. Download from the web site the latest version of java - J2SE(TM) Development Kit 5.0 Update You will download this file: jdk-1_5_0_06-windows-i586-p.exe (size: MB) 3. At the time of publication of this course, the jdk-1_5_0_06 is the latest version. However, any time you can download the most recent version of the installer from Sun s Web site. Go to and then click the following link Download JDK 5.0 Update 6. Then click the DOWNLOAD link under the Windows Platform - J2SE(TM) Development Kit 5.0 Update 6. You must accept the license agreement before downloading. Once you accept the license agreement, you are directed to a download page, where you can select and download the installer for your computer platform. Save the installer on your hard disk and keep track of where you save it. The following steps show the installation procedure on the Windows platform. 4. Starting installation of the JDK. After downloading the JDK installer double click the installer program to begin installing the JDK. The InstallShield Wizard window (Fig. 1) is displayed. Wait for the wizard to finish the configuration. Fig. 1: InstallShield Wizard for the JDK Stavros Dimitriou London South Bank University 7

8 Fig. 2: JDK license agreement 5. Accepting the license agreement. Carefully read the license agreement. Select Yes to agree to the terms (Fig. 2). [Note: If you choose not to accept the license agreement, the software will not install and you will not be able to execute or create Java applications.] 6. Choosing the installation directory for the JDK. Select the directory in which you want the JDK to be installed (Fig. 3). If you change the default installation directory, be sure to write down the exact name and location of the directory you choose, as you will need this information later in the installation process. After selecting a directory, click the Next> button to install the development tool. Stavros Dimitriou London South Bank University 8

9 Fig. 3: Choosing the installation directory for the JDK 7. Choosing the installation directory for the Java Runtime Environment (JRE). Select the directory in which you want the JRE to be installed (Fig. 4). We recommend that you choose the default installation directory. After you have selected a directory, click the Next> button to install the JRE. 8. Selecting browsers. As part of the installation, you have the option of making the Java plug-in the default Java runtime environment for Java programs called applets that run in Web browsers (Fig. 5). After you select the desired browsers click the Next> button. Stavros Dimitriou London South Bank University 9

10 Wait while the Install Wizard installs J2SE development Kit 5.0 Update 6. Fig. 4: Selecting the components of the JDK to install Fig. 5: Selecting Browser(s) 9. Finishing the installation. The program will now install the JRE. Click the Finish button to complete the installation process (Fig. 6). Stavros Dimitriou London South Bank University 10

11 Fig. 6: Completing the installation The PATH environment variable on your computer designates which directories the computer searches when looking for applications, such as the applications that enable you to compile and run your Java applications (called javac.exe and java.exe, respectively). You will now practically learn how to set the PATH environment variable on your computer. Stavros Dimitriou London South Bank University 11

12 Part C: Installing Setting the PATH Variable (This is an exercise to help you on how to set the PATH variable at your own PC) Workshop The last step before you can use the JDK is to set the PATH environment variable to indicate where the JDK s tools are installed. 1. Opening the System Properties dialog. Right click on the My Computer icon on your desktop and select Properties from the menu. The System Properties dialog (Fig. 7) appears. [Note: Your System Properties dialog may appear different than the one shown in Fig. 7, depending on your version of Microsoft Windows. This particular dialog is from a computer running Microsoft Windows XP Service pack 2. Your dialog might include different information.] Fig. 7: System Properties dialog 2. Opening the Environment Variables dialog. Select the Advanced tab at the top of the System Properties dialog (Fig. 8). Click the Environment Variables button to display the Environment Variables dialog (Fig. 9). Stavros Dimitriou London South Bank University 12

13 Select the Advanced tab Click the Environment Variables button Fig. 8: Advanced tab System Properties dialog Fig. 9: Environment Variables dialog 3. Editing the PATH variable. Scroll down inside the System variables box to select the PATH variable. Click the Edit button. This will cause the Edit System Variable dialog to appear (Fig. 10). Stavros Dimitriou London South Bank University 13

14 Fig. 10: Edit System Variable dialog 4. Changing the contents of the PATH variable. Place the cursor inside the Variable Value field. Use the left-arrow key to move the cursor to the beginning of the list. At the beginning of the list, type the name of the directory in which you placed the JDK followed by \bin; (Fig. 11). If you chose the default installation directory in Step 6 of the previous section (see Introduction: Installing the latest version of the J2SE Development Kit (JDK)), you will add C:\Program Files\Java\jdk1.5.0_06\bin; to the PATH variable here. Your PATH variable is: C:\Program Files\Java\jdk1.5.0_06\bin Fig. 11: Editing the PATH variable Click the OK button to complete the modification of the PATH variable. [Note: the default installation directory is named jdk1.5.0_06, even though the JDK is now called version 5.0.] You are now ready to begin with your Java programs! Stavros Dimitriou London South Bank University 14

15 Part D: Compiling and Executing Your First Java Application You are now ready to compile and execute our program. For this purpose, you will use the Sun Microsystems J2SE Development Kit. To prepare to compile the program, open a command window and change to the directory where the program is stored. You learned in part C how to set the PATH variable. Assume that the name of the class is Welcome. To compile a program called Welcome.java, type javac Welcome.java in the command window of your system. If the program contains no syntax errors, the preceding command creates a new file called Welcome.class (known as the class file for Welcome) containing the Java bytecodes that represent our application. When we use the java command to execute the application, these bytecodes will be executed by the JVM. Note: When attempting to compile a program, if you receive a message such as bad command or filename, javac: command not found or 'javac' is not recognized as an internal or external command, operable program or batch file, then your Java software installation was not completed properly. If you are using the J2SE Development Kit, this indicates that the system s PATH environment variable was not set properly. To execute a Java application called Welcome, type in the command window of your system. java Welcome This launches the JVM, which loads the.class file for class Welcome. Note that the.class file-name extension is omitted from the preceding command; otherwise, the JVM will not execute the program. The JVM calls method main. Stavros Dimitriou London South Bank University 15

16 Exercise 1: A simple Java Program A Java program can be written in many ways. Let us begin with a simple Java program that displays the message Welcome to Java! Problem Write a program that displays the message Welcome to Java! on the console. Solution The following listing gives the solution to the problem. // Welcome.java // Text-printing program. public class Welcome { // main method begins execution of Java application public static void main( String args[] ) { System.out.println("Welcome to Java!"); } // end method main } // end class Welcome 1. Create, Compile and Run the program. 2. Explain how you did it, demonstrate the output you got and put all this information in your logbook. Stavros Dimitriou London South Bank University 16