Java Programming Tutorials Basic to Advanced 1

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JAVA STANDARD EDITION [JAVA SE] Level-1 Basic Concepts

CONTENTS: 1. The History and Evolution of Java. 2. Java Language Basics. 3. Classes and Objects. 4. Inheritance. 5. Interfaces and Abstract Classes. 6. Packages. 7. Exception Handling. 8. Numbers and Strings. 9. Multithreaded Programming. 10. Basic I/O and Applets.

1. The History and Evolution of Java. •History and Evolution of Java. •The Java Technology. •Features of Java Language. •Types of Java Programs. •The ” HelloWorld” Application. •“HelloWorld” for Windows OS. •“HelloWorld” for Linux/Solaris. •A Closer Look at “HelloWorld” Program. • File naming rules. • Platforms /Editions of Java.

History and Evolution of Java Java was conceived by James Gosling, Patrick Naughton, Chris Worth, Ed- Frank and Mike Sheridan at Sun Microsystems. Inc USA in 1991. The language was initially called ‘Oak’ but renamed ‘Java’ in 1995. The primary motivation for the creation of Java was the need for a platform- independent (Architectural Neutral) language that could be used to create software to be embedded in various consumer electronic devices, such as Microwave Owens and Remote Controls. Many types of CPUs are used as controllers. The trouble with most other languages is that they are designed to be compiled for a specific target. Although it is possible to compile a C++ program for any type of CPU, it requires a full C++ compiler targeted for that CPU. The problem is that compilers are expensive and time consuming to create. In an attempt to find an easier and cost efficient solution, the developers began to work on a portable, platform independent language that could be used to produce code that would run on a variety of CPUs under differing environment. This efforts ultimately led to the creation of Java.

The Java Technology Java technology is both a programming language and a platform. The Java Programming Language. In the Java programming language, all source code is first written in plain text files ending with the .java extension. Those source files are then compiled into .class files by the javac compiler. A .class file does not contain code that is native to our processor; it instead contains byte codes — the intermediate code understood by the Java Virtual Machine (Java VM). The java launcher tool (Java interpreter) then runs our application with an instance of the Java Virtual Machine. Figure : An overview of the software development process

Because the Java VM is available on many different operating systems, the same .class files are capable of running on Microsoft Windows, the Solaris™ Operating System (Solaris OS), Linux, or Mac OS. Through the Java VM, the same application is capable of running on multiple platforms

The Java Platform. A platform is the hardware or software environment in which a program runs. Most platforms can be described as a combination of the operating system and underlying hardware. The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms. The Java platform has two components: • The Java Virtual Machine. • The Java Application Programming Interface (API) The Java Virtual Machine [JVM]. All language compilers translates source code in to machine code for a specific computer. Java compiler also do this. Java achieves platform- independency in the way that Java compiler produces an intermediate code known as ‘java byte-code’ for a machine that does not exists. This machine is called The ‘Java Virtual Machine’ [JVM] and it exists only inside the computer’s memory. It is a simulated computer inside the real computer and does all major functions of a real computer. The byte code is not machine specific. The machine code is generated by the Java Interpreter by acting as an intermediary between java virtual machine and the real machine. The interpreter is different for different machines.

(API) The Java Application Programming Interface The API is a large collection of ready-made software components that provide many useful capabilities. It is grouped into libraries of related classes and interfaces; these libraries are known as packages. Figure : The API and Java Virtual Machine insulate the program from the underlying hardware As a platform-independent environment, the Java platform can be a bit slower than native code.

Features of Java Language. Simple, Small & Familiar Platform Independent Object Oriented Portable Distributed High performance Multithreaded Robust & Secure Compiled & Interpreted Dynamic & Extensible Java programming language is a high-level language that can be characterized by all of the following buzzwords: Simple, Small & Familiar. Java is simple to use for professionals. Java Codes looks like a ‘C++’ code. In fact Java is a simplified version of C++. Platform Independent Java programs can be easily moved from one computer to another, anywhere any time. Changes, upgrades in OS, processors, and system resources will not force any changes in Java programs. Object Oriented. Java is a true object-oriented programming language. Almost everything in java is an object. All program codes and data resides within objects and classes. Portable. Java program can be easily moved from one computer to another computer, anywhere, any time. Distributed. Java is designed as a distributed language for creating applications on networks. It has the ability to share both data and programs. Java applications can open and access remote objects on Internet as they can do in local machines. High Performance. Java architecture is designed to reduce overheads during runtime. Multithreading enhances the overall execution speed of java programs. Multithreaded. Multithreaded means handling multiple tasks simultaneously. Java supports multithreaded programming. We needn’t wait for the application to be finished one task before beginning another. Robust & Secure. Java provides many safeguards to ensure reliable code. It has strict compile time and runtime checking for data types. It is designed as a garbage collected language. It also incorporates the concepts of exception handling which captures critical errors and eliminates any risk of crashing the system. Compiled & Interpreted. Running a Java program is a two stage process. First java compiler translates source code in to an intermediate code known as ‘byte code’. Second Java interpreter converts he byte code in to machine code that can be directly executed by the machine that is running the java program. Dynamic & Extensible. Java is capable of dynamically linking in new class libraries, methods and objects. Java programs support functions written in other languages such as C & C+ +. These functions are called native methods. Native methods are linked dynamically at runtime.

Types of Java Programs Java Programs are of two types:  Applications.  Applets. Applications are stand alone programs. They are designed to run on local machines. An Applet is a special kind of Java program that is designed to be transmitted over the Internet and automatically executed by a Java compatible web browser. An ‘Applet’ is downloaded on demand just like an image, sound or video clip.

The "Hello World!" Application OhK! It's time to write our first application! A Checklist To write our first program, we need: 1.The Java SE Development Kit 7 (JDK 7) 2.A text Editor In this example, we'll use Notepad, a simple editor included with the Windows platforms. You can easily adapt these instructions if you use a different text editor. These two items are all we need to write your first application. HelloWorld Application in Windows.

Creating Your First Application Our first application, HelloWorld.java, will simply display the greeting "Hello world!". To create this program, we will:  Create a source file: A source file contains code, written in the Java programming language, that we and other programmers can understand. We can use any text editor to create and edit source files.  Compile the source file into a .class file: The Java programming language compiler (javac) takes our source file and translates its text into instructions that the Java virtual machine (JVM) can understand. The instructions contained within this file are known as bytecodes.  Run the program The Java application launcher tool- ie., interpreter (java) uses the Java virtual machine to run our application.

Create a Source File: To create a source file, First, start the editor. We can launch the Notepad editor from the Start menu by selecting Programs > Accessories > Notepad. In a new document, type in the following code: class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } }

Save the code in a file with the name HelloWorld.java. To do this in Notepad, first choose the File > Save As menu item. Then, in the Save As dialog box: Using the Save in combo box, specify the folder (directory) where we'll save our file. In this example, the directory is worksjava on the F drive. In the File name text field, type HelloWorld.java, From the Save as type combo box, choose ‘All Files’. In the Encoding combo box, leave the encoding as ANSI. When you're finished, the dialog box should look like this.

Now click Save, and exit Notepad.

Compile the Source File into a .class File Bring up a shell, or "command," window. We can do this from the Start menu by choosing Command Prompt (Windows XP), or by choosing Run... and then entering cmd. The shell window should look similar to the following figure.

The prompt shows our current directory. When we bring up the prompt, our current directory is usually our home directory for Windows XP. To compile our source file, change our current directory to the directory where our file is located. For example, if your source directory is java which is inside works directory on the F drive, type the following command at the prompt and press Enter: F: cd WorksJava Now the prompt should change to F:WORKSjava> Changing directory on an alternate drive.

If you enter dir at the prompt, you should see your source file, as the following figure shows. Directory listing showing the .java source file.

Now you are ready to compile. At the prompt, type the following command and press Enter.  javac HelloWorld.java The compiler has generated a bytecode file, HelloWorld.class. At the prompt, type dir to see the new file that was generated, as shown in the following figure. Directory listing, showing the generated .class file Now that you have a .class file, you can run your program.

Run the Program In the same directory, enter the following command at the prompt:  java HelloWorld The next figure shows what we should now see: Congratulations! You have done !. Your program works!

"Hello World!" for Solaris OS and Linux It's time to write our first application! These detailed instructions are for users of Solaris OS and Linux. A Checklist To write your first program, we'll need: The Java SE Development Kit 6 (JDK 6) A Text Editor In this example, we'll use vi, an editor available for many UNIX-based platforms. We can easily adapt these instructions if we use a different text editor, such as pico or emacs. These two items are all we need to write our first application.

Creating Our First Application Our first application, HelloWorldApp, will simply display the greeting "Hello world!". To create this program, we will:  Create a source file A source file contains code, written in the Java programming language, that we and other programmers can understand. we can use any text editor to create and edit source files.  Compile the source file into a .class file The Java programming language compiler (javac) takes our source file and translates its text into instructions that the Java virtual machine can understand. The instructions contained within this .class file are known as bytecodes. Run the program The Java application launcher tool ie., the Java interpreter (java) uses the Java virtual machine to run our application.

Create a Source File To create a source file, First, open a shell, or "terminal," window. A new terminal window.

When we first bring up the prompt, our current directory will usually be our home directory. We can change our current directory to our home directory at any time by typing cd at the prompt and then pressing Return. The source files we create should be kept in a separate directory. we can create a directory by using the command mkdir. For example, to create the directory java in your home directory, use the following commands: $ mkdir java To change our current directory to this new directory, we then enter: $ cd java Now we can start creating your source file. Start the vi editor by typing ‘vi’ at the prompt and pressing Return. Type the following code into the new opened buffer: class HelloWorldApp{ public static void main(String[] args) { System.out.println("Hello World!"); } }

Save the code in a file with the name HelloWorld.java You can press Esc key followed by a column ( : ) and ‘wq’ to exit vi. Compile the Source File into a .class File Bring up another shell window. To compile our source file, change our current directory to the directory where our file is located. For example, if our source directory is /home/java, type the following command at the prompt and press Return:

$ cd /home/java If we enter pwd at the prompt, we should see the current directory, which in this example has been changed to /home/jdoe/java. If we enter ls at the prompt, we should see your file. Now are ready to compile the source file. At the prompt, type the following command and press Return. $ javac HelloWorldApp.java The compiler has generated a bytecode file, HelloWorldApp.class. Results of the ls command, showing the .java source file.

Now that you have a .class file, you can run your program. Results of the ls command, showing the generated .class file.

Run the Program In the same directory, enter at the prompt: java HelloWorldApp The next figure shows what we should now see. The output prints "Hello World!" to the screen Congratulations! You have done !. Your program works!

A Closer Look at “HelloWorld.java” Program class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } } Here ‘class HelloWorld’ declares a class. Everything must be placed inside a class. Here ‘class’ is a keyword and ‘HelloWorld’ is the class name. public static void main(String[] args) – defines a method main( ). Every Java application program must include a main() method. This I the starting point for the interpreter to begin the execution of the program. Here the keyword ‘public’ is an access specifier that declares the main method as an unprotected and there for making it accessible to all other classes.

The ‘static’ keyword declares this method as one that belongs to the entire class and not a part of any objects of the class. The main must be declared as static because the interpreter uses this method before any objects are created. The ‘void’ states that the main method does not return any value. Any information that we want to pass to a method is received by variables specified within the sets of parentheses. The main method accepts a single argument: an array of elements of type String. public static void main(String[] args) This array is the mechanism through which the runtime system passes information to your application. For example: java HelloWorld arg1 arg2 Each string in the array is called a command-line argument. Command-line arguments let users affect the operation of the application without recompiling it. For example, a sorting program might allow the user to specify that the data be sorted in descending order with this command-line argument: -descending The "Hello World!" application ignores its command-line arguments.

The line System.out.println("Hello World!"); prints the string inside the parentheses on standard output. Here ‘System’ is a class which includes a field called ‘out’. This has a method named println( ) which does the actual displaying of text. A Second Program. /** The MyWishes class implements an application that simply prints two lines to the standard output. */ class MyWishes { public static void main(String[] args) { System.out.println("Hello Duke!"); // Display the string. System.out.println(“Welcome To Java World”); } }

Source Code Comments. The following yellow colored text defines the comments of the MyWishes application: /** The MyWishes class implements an application that simply prints two lines to the standard output. */ class MyWishes { public static void main(String[] args) { System.out.println("Hello Duke!"); // Display the string. System.out.println(“Welcome To Java World”); } } Comments are ignored by the compiler but are useful to other programmers to give information about the program.

The Java programming language supports three kinds of comments: /* text */ The compiler ignores everything from /* to */. /** documentation */ This indicates a documentation comment (doc comment, for short). The compiler ignores this kind of comment, just like it ignores comments that use /* and */. The javadoc tool uses doc comments when preparing automatically generated documentation. // text The compiler ignores everything from // to the end of the line.

A File name can be any legal identifier — an unlimited-length sequence of Unicode letters and digits, beginning with a letter, the dollar sign "$", or the underscore character "_". The convention, however, is to always begin our file names with a letter, not "$" or "_". Additionally, the dollar sign character, by convention, is never used at all. Similar convention exists for the underscore character; while it's technically legal to begin your variable's name with "_", this practice is discouraged. File Naming Rules. Every programming language has its own set of rules and conventions for the kinds of names that we're allowed to use, and the Java programming language is no different. The rules and conventions for naming our files can be summarized as follows: File names are case-sensitive. Java treats capital and small letters differently. Subsequent characters may be letters, digits, dollar signs, or underscore characters. Conventions (and common sense) apply to this rule as well. When choosing a name for your file use full words instead of cryptic abbreviations.

 The first letter of the file name, by convention, be capitalized. If the name we choose consists of only one word, spell the rest letters in lowercase letters. If it consists of more than one word, capitalize the first letter of each words. Examples are HelloWorld.java MyFirstProgram.java Temperature.java Usually the class name is given as the file name in Java. If a program contains multiple classes, the name of the class which contains main method is given as the class name. White space is not permitted.

Platforms/Editions of Java There are four platforms/editions of Java programming language:  Java Platform, Standard Edition (Java SE).  Java Platform, Enterprise Edition (Java EE).  Java Platform, Micro Edition (Java ME).  Java FX. All Java Platforms consists of a Java Virtual Machine (JVM) and an Application Programming Interface (API). This allows applications written for that platform to run on any compatible system with all the advantages of Java programming language.  Java SE Java SE’s API provides the core functionality of Java programming language. It defines everything from the basic types and objects of the language to the high-level classes that are used for networking, security, database access, GUI development and XML parsing. Java SE platform consists of JVM, development tools, deployment technologies, and other class libraries and toolkits commonly used in Java technology applications.

 Java EE The Java EE platform is built on top of the Java SE platform. The Java EE platform provides an API and runtime environment for developing and running large-scale, multi-tiered, scalable, reliable, and secure network applications.  Java ME The Java ME platform provides an API and a small-footprint virtual machine for running Java programming language applications on small devises, like mobile phones. The API is a subset of Java SE API, along with special class libraries useful for small devise application development.  Java FX Java FX technology is a platform for creating rich internet applications written in Java FX script. Java FX script is a statically typed declarative language that is compiled to Java technology ‘byte code’, which can then be run on Java VM. Applications written for the Java FX platform can include and link to Java programming language classes, and may be client of Java EE platform services.

Java Programming Tutorials Basic to Advanced 1

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