Compiling and Running A Simple Program
This lesson explains how to write, compile, and run a simple program written in the Java TM language (Java program) that tells your computer to print a one-line string of text on the console.
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<p><font face="Verdana">The computer age is here to stay.
Households and businesses all over the world use computers in
one way or another because computers help individuals and
businesses perform a wide range of tasks with speed, accuracy,
and efficiency. Computers can perform all kinds of tasks ranging
from running an animated 3D graphics application with background
sound to calculating the number of vacation days you have coming
to handling the payroll for a Fortune 500 company.</font>
<p><font face="Verdana">When you want a computer to perform
tasks, you write a program. A program is a sequence of
instructions that define tasks for the computer to execute. This
lesson explains how to write, compile, and run a simple program
written in the Java<font size="-2"><sup>TM</sup></font> language
(Java program) that tells your computer to print a one-line
string of text on the console.</font>
<p><font face="Verdana">But before you can write and compile
programs, you need to understand what the Java platform is, and
set your computer up to run the programs.</font>
<ul>
<li><a href="#platform"><font face="Verdana">A Word About the
Java Platform</font></a>
<li><a href="#setup"><font face="Verdana">Setting Up Your
Computer</font></a>
<li><a href="#simple"><font face="Verdana">Writing a Program</font></a>
<li><a href="#comp"><font face="Verdana">Compiling the Program</font></a>
<li><a href="#run"><font face="Verdana">Interpreting and
Running the Program</font></a>
<li><a href="#debug"><font face="Verdana">Common Compiler and
Interpreter Problems</font></a>
<li><a href="#comm"><font face="Verdana">Code Comments</font></a>
<li><a href="#api"><font face="Verdana">API Documentation</font></a>
<li><a href="#more"><font face="Verdana">More Information</font></a></li>
</ul>
<font face="Verdana, Arial, Helvetica, sans-serif">
<hr>
<a name="platform"></a></font>
<h3><font face="Verdana">A Word About the Java Platform</font></h3>
<font face="Verdana">The Java platform consists of the Java
application programming interfaces (APIs) and the Java<a href="#TJVM"><sup>1</sup></a>
virtual machine (JVM).</font>
<p><font face="Verdana"><img align="left" src="http://www.planet-source-code.com/vb/tutorial/java/images/platform.gif" >
Java APIs are libraries of compiled code that you can use in
your programs. They let you add ready-made and customizable
functionality to save you programming time.</font>
<p><font face="Verdana">The simple program in this lesson uses a
Java API to print a line of text to the console. The console
printing capability is provided in the API ready for you to use;
you supply the text to be printed.</font>
<p><font face="Verdana">Java programs are run (or interpreted)
by another program called the Java VM. If you are familiar with
Visual Basic or another interpreted language, this concept is
probably familiar to you. Rather than running directly on the
native operating system, the program is interpreted by the Java
VM for the native operating system. This means that any computer
system with the Java VM installed can run Java programs
regardless of the computer system on which the applications were
originally developed.</font>
<p><font face="Verdana">For example, a Java program developed on
a Personal Computer (PC) with the Windows NT operating system
should run equally well without modification on a Sun Ultra
workstation with the Solaris operating system, and vice versa. <a name="setup"></a></font>
<h3><font face="Verdana">Setting Up Your Computer</font></h3>
<font face="Verdana">Before you can write and run the simple
Java program in this lesson, you need to install the Java
platform on your computer system.</font>
<p><font face="Verdana">The Java platform is available free of
charge from the <a href="http://java.sun.com/products/jdk/1.2/" target="_blank">java.sun.com</a>
web site. You can choose between the Java® 2 Platform software
for Windows 95/98/NT or for Solaris. The download page contains
the information you need to install and configure the Java
platform for writing and running Java programs.</font><font face="Verdana, Arial, Helvetica, sans-serif">
<p>
<blockquote>
<hr>
</font><font face="Verdana"><strong>Note:</strong> Make sure you
have the Java platform installed and configured for your system
before you try to write and run the simple program presented
next.</font><font face="Verdana, Arial, Helvetica, sans-serif">
<hr>
</blockquote>
<a name="simple"></a></font>
<h3><font face="Verdana">Writing a Program</font></h3>
<font face="Verdana">The easiest way to write a simple program
is with a text editor. So, using the text editor of your choice,
create a text file with the following text, and be sure to name
the text file <code>ExampleProgram.java</code>. Java programs
are case sensitive, so if you type the code in yourself, pay
particular attention to the capitalization.</font>
<pre><font face="Verdana">//A Very Simple Example
class ExampleProgram {
public static void main(String[] args){
System.out.println("I'm a Simple Program");
}
}
</font></pre>
<font face="Verdana">Here is the <a href="http://www.planet-source-code.com/vb/tutorial/java/samples/ExampleProgram.java">ExampleProgram.java</a>
source code file if you do not want to type the program text in
yourself. <a name="comp"></a></font>
<h3><font face="Verdana">Compiling the Program</font></h3>
<font face="Verdana">A program has to be converted to a form the
Java VM can understand so any computer with a Java VM can
interpret and run the program. Compiling a Java program means
taking the programmer-readable text in your program file (also
called source code) and converting it to bytecodes, which are
platform-independent instructions for the Java VM.</font>
<p><font face="Verdana">The Java compiler is invoked at the
command line on Unix and DOS shell operating systems as follows:</font>
<pre><font face="Verdana"> javac ExampleProgram.java
</font></pre>
<font face="Verdana, Arial, Helvetica, sans-serif">
<blockquote>
<hr>
</font><font face="Verdana"><strong>Note:</strong> Part of the
configuration process for setting up the Java platform is
setting the class path. The class path can be set using either
the <code>-classpath</code> option with the <code>javac</code>
compiler command and <code>java</code> interpreter command, or
by setting the <code>CLASSPATH</code> environment variable. You
need to set the class path to point to the directory where the <code>ExampleProgram</code>
class is so the compiler and interpreter commands can find it.
See <a href="http://java.sun.com/products/jdk/1.2/docs/tooldocs/tools.html" target="_blank">Java
2 SDK Tools</a> for more information.</font><font face="Verdana, Arial, Helvetica, sans-serif">
<hr>
</blockquote>
<a name="run"></a></font>
<h3><font face="Verdana">Interpreting and Running the Program</font></h3>
<font face="Verdana">Once your program successfully compiles
into Java bytecodes, you can interpret and run applications on
any Java VM, or interpret and run applets in any Web browser
with a Java VM built in such as Netscape or Internet Explorer.
Interpreting and running a Java program means invoking the Java
VM byte code interpreter, which converts the Java byte codes to
platform-dependent machine codes so your computer can understand
and run the program.</font>
<p><font face="Verdana">The Java interpreter is invoked at the
command line on Unix and DOS shell operating systems as follows:</font>
<pre><font face="Verdana"> java ExampleProgram
</font></pre>
<font face="Verdana">At the command line, you should see:</font>
<pre><font face="Verdana"> I'm a Simple Program
</font></pre>
<font face="Verdana">Here is how the entire sequence looks in a
terminal window:</font>
<p><font face="Verdana"><img src="http://www.planet-source-code.com/vb/tutorial/java/images/examprog.gif"></font>
<p>
<h3><font face="Verdana">Common Compiler and Interpreter
Problems</font></h3>
<font face="Verdana">If you have trouble compiling or running
the simple example in this lesson, refer to the <a href="http://java.sun.com/docs/books/tutorial/getStarted/problems/index.html" target="_blank">Common
Compiler and Interpreter Problems</a> lesson in <a href="http://java.sun.com/docs/books/tutorial/trailmap.html" target="_blank">The
Java Tutorial</a> for troubleshooting help. <a name="comm"></a></font>
<h3><font face="Verdana">Code Comments</font></h3>
<font face="Verdana">Code comments are placed in source files to
describe what is happening in the code to someone who might be
reading the file, to comment-out lines of code to isolate the
source of a problem for debugging purposes, or to generate API
documentation. To these ends, the Java language supports three
kinds of comments: double slashes, C-style, and doc comments.</font>
<h4><font face="Verdana">Double Slashes</font></h4>
<font face="Verdana">Double slashes (<code>//</code>) are used
in the C++ programming language, and tell the compiler to treat
everything from the slashes to the end of the line as text.</font>
<pre><font face="Verdana">//A Very Simple Example
class ExampleProgram {
public static void main(String[] args){
System.out.println("I'm a Simple Program");
}
}
</font></pre>
<h4><font face="Verdana">C-Style Comments</font></h4>
<font face="Verdana">Instead of double slashes, you can use
C-style comments (<code>/* */</code>) to enclose one or more
lines of code to be treated as text.</font>
<pre><font face="Verdana">/* These are
C-style comments
*/
class ExampleProgram {
public static void main(String[] args){
System.out.println("I'm a Simple Program");
}
}
</font></pre>
<h4><font face="Verdana">Doc Comments</font></h4>
<font face="Verdana">To generate documentation for your program,
use the doc comments (<code>/** */</code>) to enclose lines of
text for the <code>javadoc</code> tool to find. The <code>javadoc</code>
tool locates the doc comments embedded in source files and uses
those comments to generate API documentation.</font>
<pre><font face="Verdana">/** This class displays a text string at
* the console.
*/
class ExampleProgram {
public static void main(String[] args){
System.out.println("I'm a Simple Program");
}
}
</font></pre>
<font face="Verdana">With one simple class, there is no reason
to generate API documentation. API documentation makes sense
when you have an application made up of a number of complex
classes that need documentation. The tool generates <code>HTML</code>
files (Web pages) that describe the class structures and contain
the text enclosed by doc comments. The <a href="http://java.sun.com/products/jdk/javadoc/index.html" target="_blank">javadoc
Home Page</a> has more information on the <code>javadoc</code>
command and its output. <a name="api"></a></font>
<h3><font face="Verdana">API Documentation</font></h3>
<font face="Verdana">The Java platform installation includes API
Documentation, which describes the APIs available for you to use
in your programs. The files are stored in a <code>doc</code>
directory beneath the directory where you installed the
platform. For example, if the platform is installed in <code>/usr/local/java/jdk1.2</code>,
the API Documentation is in <code>/usr/local/java/jdk1.2/doc/api</code>.
<a name="more"></a></font>
<h3><font face="Verdana">More Information</font></h3>
<font face="Verdana">See <a href="http://java.sun.com/products/jdk/1.2/docs/tooldocs/tools.html" target="_blank">Java
2 SDK Tools</a> for more information on setting the class path
and using the <code>javac</code>, and <code>java</code>
commands.</font>
<p><font face="Verdana">See <a href="http://java.sun.com/docs/books/tutorial/getStarted/problems/index.html" target="_blank">Common
Compiler and Interpreter Problems</a> lesson in <a href="http://java.sun.com/docs/books/tutorial/trailmap.html" target="_blank">The
Java Tutorial</a> for troubleshooting help.</font>
<p><font face="Verdana">The <a href="http://java.sun.com/products/jdk/javadoc/index.html" target="_blank">javadoc
Home Page</a> has more information on the <code>javadoc</code>
command and its output.</font>
<p><font face="Verdana">You can also view the API Documentation
for the Java 2 Platform on the <a href="http://java.sun.com/products/jdk/1.2/docs/api/index.html" target="_blank">java.sun.com</a>
site.</font>
<p><font face="Verdana">_______<br>
<a name="TJVM"><sup>1</sup></a> As used on this web site, the
terms "Java virtual machine" or "JVM" mean a
virtual machine for the Java platform.</font>
<hr>
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<font size="2">
<p><font face="verdana,arial"><b>Reprinted with permission from
the <a href="http://developer.java.sun.com/developer/" target="_blank">Java
Developer Connection(SM)</a><br>
Copyright <a href="http://www.sun.com" target="_blank">Sun
Microsystems Inc</a>.</b></font></p>
</font>
<p align="right"><font face="Verdana" size="-1">[<a href="#top">TOP</a>]</font></p>
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<!-- Copyright Insert -->
Imports System.Data.OleDb
Imports ADODB
Public Class Form1
Inherits System.Windows.Forms.Form
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
RecordSetToDataSet("ser_amp_bd2", "pubs")
End Sub
Private Function RecordSetToDataSet(ByVal Server As String, _
ByVal DataBase As String)
Dim cnn As Connection = New ADODB.Connection()
Dim rs As Recordset = New ADODB.Recordset()
'--Open connection--
cnn.open("PROVIDER=SQLOLEDB;DATA SOURCE=" & Server & ";" & _
"INITIAL CATALOG=" & DataBase & ";INTEGRATED SECURITY=SSPI;")
'--create recordset--
'--<any table> name of table in your database
Dim sql As String = "select * from authors"
rs.open(sql, cnn, CursorTypeEnum.adOpenForwardOnly, LockTypeEnum.adLockReadOnly, 0)
Dim dadapter As New OleDbDataAdapter()
Dim ddataset As New DataSet()
'--Move rs to dataset--
dadapter.Fill(ddataset, rs, "result")
'--Fill a grid--
grd.DataSource = ddataset.Tables("result")
'--Close Connection--
cnn.Close()
End Function
End Class
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