Showing posts with label Java Tutorial. Show all posts
Showing posts with label Java Tutorial. Show all posts

Thursday, 3 November 2016

Published 04:48:00 by with 0 comment

How to display Date and Time in Javascript

Hi,
In this script, I will show you how to display the date and time in real time in a web page using Javascript.


The script is simple, we will use the Javascript Object Date to get the date and the time. We will display the month in words(January, February...).

This is the code:
date_time.js
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function date_time(id)
{
        date = new Date;
        year = date.getFullYear();
        month = date.getMonth();
        months = new Array('January', 'February', 'March', 'April', 'May', 'June', 'Jully', 'August', 'September', 'October', 'November', 'December');
        d = date.getDate();
        day = date.getDay();
        days = new Array('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday');
        h = date.getHours();
        if(h<10)
        {
                h = "0"+h;
        }
        m = date.getMinutes();
        if(m<10)
        {
                m = "0"+m;
        }
        s = date.getSeconds();
        if(s<10)
        {
                s = "0"+s;
        }
        result = ''+days[day]+' '+months[month]+' '+d+' '+year+' '+h+':'+m+':'+s;
        document.getElementById(id).innerHTML = result;
        setTimeout('date_time("'+id+'");','1000');
        return true;
}
date_time.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>Display Date and Time in Javascript</title>
        <script type="text/javascript" src="date_time.js"></script>
    </head>
    <body>
            <span id="date_time"></span>
            <script type="text/javascript">window.onload = date_time('date_time');</script>
    </body>
</html>
I hope this script will be useful.
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Monday, 19 September 2016

Published 14:59:00 by with 0 comment

Java code structure and syntax


In the previous section, you tidied up your code a bit.

Here's what your coding window should look like now:




You can see we have the package name first. Notice how the line ends with a semicolon. If you miss the semicolon out, the programme won't compile:
package firstproject;
The class name comes next:

public class FirstProject {
}


You can think of a class as a code segment. But you have to tell Java where code segments start and end. You do this with curly brackets. The start of a code segment is done with a left curly bracket { and is ended with a right curly bracket }. Anything inside of the left and right curly brackets belong to that code segment.
What's inside of the left and right curly brackets for the class is another code segment. This one:


public static void main( String[ ] args ) {

}


The word "main" is the important part here. Whenever a Java programme starts, it looks for a method called main. (A method is just a chunk of code. You'll learn more about these later.) It then executes any code within the curly brackets for main. You'll get error messages if you don't have a main method in your Java programmes. But as its name suggest, it is the main entry point for your programmes.

The blue parts before the word "main" can be ignored for now.
(If you're curious, however, public means that the method can be seen outside of this class; static means that you don't have to create a new object; and void means it doesn't return a value - it just gets on with it. The parts between the round brackets of main are something called command line arguments. Don't worry if you don't understand any of that, though.)
The important point to remember is that we have a class called FirstProject. This class contains a method called main. The two have their own sets of curly brackets. But the main chunk of code belongs to the class FirstProject.

In the next part, you'll learn how to run your Java programmes.

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Published 14:31:00 by with 0 comment

How to Add a Comment in your Java source code

This section will take you through on how to add a comment in your Java source code. Comment hopes the Programmer to understand what a particular line of code is to perform.
    
 
When you create a New Project in NetBeans, you'll notice that some text is greyed out, with lots of slashes and asterisks:

The greyed-out areas are comments. When the programme runs, comments are ignored. So you can type whatever you want inside of your comments. But it's usual to have comments that explain what is you're trying to do. You can have a single line comment by typing two slashes, followed by your comment:

//This is a single line comment
If you want to have more than one line, you can either do this:
//This is a comment spreading
//over two lines or more
Or you can do this:
/*
This is a comment spreading
over two lines or more
*/


In the comment above, note how it starts with /*. To end the comment, we have */ instead.
There's also something called a Javadoc comment. You can see two of these in the coding image on the previous page. A Javadoc comment starts with a single forward slash and two asterisks (/**) and ends with an asterisk and one slash ( */ ). Each line of the comment starts with one asterisk:


/**
*This is a Javadoc comment
*/


Javadoc comments are used to document code. The documented code can then be turned into an HTML page that will be helpful to others. You can see what these look like by clicking Run from the menu at the top of NetBeans. From the Run menu, select Generate Javadoc. There's not much to see, however, as you haven't written any code yet!
At this stage of your programming career, you can delete the comments that NetBeans generates for you. Here's our code again with the comments deleted:



In the next part, you'll learn about the structure of the above code, and how to run your programmes.
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Published 14:19:00 by with 0 comment

The NetBeans Software


When you first run NetBeans, you'll see a screen:
The NetBeans Software - First Start
You may have to drum your fingers and wait a while, as it's not the fastest thing in the world.
    


To start a new project, click on File > New Project from the NetBeans menu at the top. You'll see the following dialogue box appear:





We're going to be create a Java Application, so select Java under Categories, and then Java Application under Projects. Click the Next button at the bottom to go to step two:



In the Project Name area at the top, type a Name for your Project. Notice how the text at the bottom changes to match your project name (in the text box to the right of Create Main Class):
firstproject.Main
If we leave it like that, the Class will have the name Main. Change it to FirstProject:


Now, the Class created will be called FirstProject, with a capital "F", capital "P". The package is also called firstproject, but with a lowercase "f" and lowercase "j".
The default location to save your projects appears in the Project Location text box. You can change this, if you prefer. NetBeans will also create a folder with your project name, in the same location. Click the Finish button and NetBeans will go to work creating all the necessary files for you.
When NetBeans returns you to the IDE, have a look at the Projects area in the top left of the screen (if you can't see this, click Window > Projects from the menu bar at the top of the software):


Click the plus symbol to expand your project, and you'll see the following:


Now expand Source Packages to see your project name again. Expand this and you'll see the Java file that is your source code.






This same source code should be displayed to the right, in the large text area. It will be called FirstProject.java. If you can't see a code window, simply double click FirstProject.java in your Projects window above. The code will appear, ready for you to start work.
The coding window that appears should look like this (we've changed the author's name):


One thing to note here is that the class is called FirstProject:

public class FirstProject {

This is the same name as the java source file in the project window: FirstProject.java. When you run your programmes, the compiler demands that the source file and the class name match. So if your .java file is called firstProject but the class is called FirstProject then you'll get an error on compile. And all because the first one is lowercase "f" and the second one uppercase.
Note that although we've also called the package firsproject, this is not necessary. We could have called the package someprogramme. So the name of the package doesn't have to be the same as the java source file, or the class in the source file: it's just the name of the java source file and the name of the class that must match.





In the next part, you'll learn about Java comments.
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Published 13:15:00 by with 0 comment

Java For Complete Beginners

One of the difficult things about getting started with Java is installing everything you need. Even before you write a single line of code, the headaches begin! Hopefully, the following sections will make life easier for you.
  

We're going to write all our code using a free piece of software called NetBeans. This is one of the most popular IDEs (Interface Development Environment) in the world for writing Java programmes. You'll see what it looks like shortly. But before NetBeans will work, it needs you to install the necessary Java components and files. First up is something called the Java Virtual Machine.

The Java Virtual Machine

Java is platform independent. This means that it will run on just about any operating system. So whether your computer runs Windows, Linux, Mac OS, it's all the same to Java! The reason it can run on any operating system is because of the Java Virtual Machine. The Virtual Machine is a programme that processes all your code correctly. So you need to install this programme (Virtual Machine) before you can run any Java code.
Java is owned by a company called Sun Microsystems, so you need to head over to Sun's website to get the Java Virtual Machine, also known as the Java Runtime Environment (JRE). Try this page first:
You can check to see if you already have the JRE on your computer by clicking the link "Do I have Java?". You'll find this link under the big Download button at the top of the page. (Unless Sun have changed things around, again!) When you click the link, your computer will be scanned for the JRE. You will then be told whether you have it or not. If not, you'll be given the opportunity to download and install it.
Or you could just head over to this page:
The "manual" in the above links means "manual download". The page gives you download links and instructions for a wide variety of operating systems.
After downloading and installing, you may need to restart you computer. When you do, you will have the Java Virtual Machine.


The Java Software Development Kit

At this stage, you still can't write any programmes. The only thing you've done is to install software so that Java programmes can be run on your computer. To write code and test it out, you need something called a Software Development kit.
Java's Software Development Kit can currently be downloaded from here:
The one we're going to be using is called Java SE. (The SE stands for Standard Edition.). Click on that link, then on "Java SE (JDK) 6 Download". You'll then find yourself on a page with a bewildering list of options to download. Because we're going to be using NetBeans, locate this:
JDK 6 Update X with NetBeans 6.x
Click the Download link to be taken to yet another page. Click the top download to be taken to a page that asks you to select your operating system. Click Continue to finally get the download you need. A word of warning, though - this download will be big, at over a 130 megabytes at the time of writing! Once you've downloaded the JDK and NetBeans, install it on your computer.
We're going to be using NetBeans to write our code. Before launching the software, however, here's how things work in the world of Java.

How things work in Java

You write the actual code for your programmes in a text editor. (In NetBeans, there's a special area for you to write code.) The code is called source code, and is saved with the file extension .java. A programme called Javac is then used to turn the source code into Java Byte Code. This is known as compiling. After Javac has finished compiling the Java Byte Code, it creates a new file with the extension .class. (At least, it does if no errors are detected.) Once the class file has been created, it can be run on the Java Virtual Machine. So:
  • Create source code with the extension .java
  • Use Javac to create (compile) a file ending in .class
  • Run the compiled class
NetBeans handles all the creating and compiling for you. Behind the scenes, though, it takes your sources code and creates the java file. It will launch Javac and compile the class file. NetBeans can then run your programme inside its own software. This saves you the hassle of opening up a terminal window and typing long strings of commands,
Now that you have a general idea of how Java works, launch your NetBeans software. Then click the link below to go to continue with the lesson
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