Introduction and Review of Java: Part 1. Basic Introduction and Installation of Tools

Transcription

1 1 Introduction and Review of Java: Part 1 Basic Introduction and Installation of Tools

2 2 The Java Programming Language Note: these slides are based on figures and text obtained from: index.html You can download the Java Tutorials from the Sun Download Center.

3 3 The Java Programming Language The design requirements of the Java language are driven by the nature of the computing environments in which software must be deployed Today s computing environment is heterogeneous, distributed network based. Simple Object Oriented Distributed Multithreaded Dynamic Architecture neutral Portable High performance Robust Secure

4 4 Java Development Process 1. Source code is written in plain text files: names ending with.java 2. The javac compiler translates (compiles) the source files into.class files. Class files contain bytecodes: the machine language of the Java Virtual Machine (Java VM). Class files do not contain code native to your processor. 3. The java program runs your application on the VM, by interpreting the bytecodes and converting them into the native machine code of your machine. javac.exe java.exe

5 5 Architecture Neutral and Portable Because the Java VM is available on many different operating systems, the same.class files are capable of running on Microsoft Windows, the Solaris TM Operating System (Solaris OS), Linux, or Mac OS

6 6 The Java Platform Microsoft Windows, Linux, Solaris OS, and Mac OS Harware and Software based platforms. Java Is a software based platform, consisting of The Java Virtual Machine. The Java Application Programming Interface (API). Large collection of libraries, stored in packages.

7 7 JAVA Development Tools In this course we use Notepad ++ to create source files The javac compiler to compile our programs. The java launcher to run them. The API documentation as the Java API reference. Primitive debugging tools. Such as old fashion analysis and print statements. Netbeans, a Java based Integrated Development Environment Breakpoint, stepping through statements, etc.

8 8 Application Programming Interface Of course, your programs may contain your custom classes and methods, but a significant part of your programs will include pre-built classes and methods offered by Java. The API provides the core functionality of the Java programming language. Offers a wide array of useful classes ready for use in your own applications. To view the API documentation online Google: java api 7

9 9 Development Techniques In this course, we will use two techniques to develop java programs: 1. Command-line interface for developing programs Windows: command prompt Notepad ++ to create source files 2. Integrated Development Environment (IDE) Netbeans: an integrated development environment You can create and edit source code (*.java files); compile and build projects; debug projects; and run programs all within the IDE.

10 Command Line Technique 10

11 11 Check List 1. The Java SE Development Kit 7 (jdk1.7.0_67) 2. A text editor Such as Notepad++ Homework: download and install the above.

12 12 Check List 1. Note: executable files are stored in the bin directory

13 13 Basic Development Steps 1. Create a source file Use Notepad++ 2. Open a command window Compile the source file, thus creating a *.class file javac *.java Run the program java *.class

14 Creating a Source File /* Source File: HelloWorldApp.java */ The HelloWorldApp class implements an application that simply prints "Hello World!" to standard output. class HelloWorldApp { public static void main(string[] args) { // Display a string. System.out.println("Hello World!"); } } 14

15 Using Notepad++ 15

16 16 Compiling a Source File (1) Bring up a command prompt window. You can do this: Start->All Programs->Accessories->Command Prompt Start, and then type cmd in the search window

17 17 Compiling a Source File (2) Change your current directory to the directory where your file is located.

18 18 Compiling a Source File (3) Now compile the.java file by running the command: javac HelloWorldApp.java

19 19 Running a Class File (1) Now run the.class file by running the command: java helloworldapp

20 Common Problems System Problems Example: after you type: javac SourceFileName.java the OS gives you a response: 'javac' is not recognized as an internal or external command,... This means the OS can t find the java.exe program. Solution Provide the path to javac.exe explicitly on the command line C:\Program Files\Java\jdk1.7.0_67\bin\javac.exe OR, store the path in the PATH environment variable: 20

21 21 Storing a Path Control Panel, and locate Advanced System Settings Click on the Environment Variables button

22 22 Storing a Path Ensure the path to javac.exe is stored in the PATH environment variable for both User and System variables Click on PATH, then click on Edit Add path (C:\Program Files\Java\jdk1.7.0_67\bin) to current path

23 23 Syntax Problems Example: testing.java:14: `;' expected. System.out.println("Input has " + count + " chars.") ^ 1 error

24 24 Compiler Checking Problems Semantic Errors, e.g., testing.java:13: Variable count may not have been initialized. count++ ^ 1 error

25 25 Runtime Errors Error Messages from the JVM, e.g., Exception in thread main java.lang.noclassdeffounderror: HelloWorldApp If you receive this error, java cannot find your bytecode file, HelloWorldApp.class.

26 IDE Technique 26

27 27 Check List 1. The Java SE Development Kit 7 (jdk1.7.0_67) 2. Netbeans IDE Download and install NetBeans IDE 8.0 Homework: download and install Netbeans

28 28 Basic Development Steps 1. Using Netbeans IDE: Create project and source code (*.java files) Compile and build your project Debug your project Run your project

29 29 See Netbeans Tutorial tml

30 Brief Intro To Java Language 30

31 31 Source Code Comments The Java programming language supports three kinds of comments: /* text */ The compiler ignores everything from /* to */. /** documentation */ The javadoc tool uses doc comments when preparing automatically generated documentation. // text The compiler ignores everything from // to the end of the line.

32 32 The HelloWorldApp Class Definition class HelloWorldApp { public static void main(string[] args) { System.out.println( Hello World! ); // Display the string Hello World!. } } The most basic form of a class definition is: class name {... } The keyword class begins the class definition for a class named name, and the code appears between the opening and closing curly braces.

33 33 The main Method In Java, every application must contain a main method whose signature is: public static void main(string[] args) The main method is the entry point for your application. The main method accepts a single argument: an array of elements of type String. This array is the mechanism through which the runtime system passes information to your application. Each string in the array is called a command-line argument.

34 34 Note: When you run the helloworldapp.class file, you won t add any command line arguments, and so none were passed to the main method. In this case the application does not require any command line arguments, but other application may.

35 35 Printing class HelloWorldApp { public static void main(string[] args) { System.out.println( Hello World! ); // Display the string Hello World!. } } System.out.println("Hello World!"); uses the System class from the core library (Java API) to print the Hello World! message to standard output.