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manish174 16Oct2010 22:22

Packages - The Most Powerful Feature of Java
 
Today we will discuss Java packages. This is one of the most important features in Java. Java comes with many pre-listed packages. Knowingly or unknowingly, you may have used them in your code. I will explain this later on. Even if you are a beginner you had used Java package. First of all we will learn what Java package is, then what its features, its importance are and how to use them in your program code.

What is Java Package?



The simplest example that will give you a most satisfactory explanation is, packages are like your book shelf. In your book shelf, you arrange school books in a row; in another row you arrange your comic books, your novels, your CD and many more. Similarly, Java also used several shelves to arrange similar kind of codes files that are used by programmers. These shelves are known as Java package. Also you must have heard about Java runtime environment ( jre ). When we compile a code it directly interact jre and use the default package which was set by Java. And the package is "java.lang". This default package is already imported in your program code. That’s why whenever we need to use the classes of java.lang package we don’t need to import this package. For other packages we need to import them explicitly.

Java Package - Importance/features



The one of the most important feature of Java package is that you can create your own package and import it in your program code without creating a .jar file. You simply need to set the classpath of your command line interpreter. For example, if you frequently use the code to calculate the area, then instead of writing the code to calculate the area in each program code you can simply write the code in a separate file and compile it. Then set the classpath of that particular class in your command line interpreter. Now you don’t need to write the same code again and again.

How to use packages in your Program Code?



Part A : Using Sun’s Java package.
In this part we will learn how to use pre-existing package. Some of the most commonly used Java packages are

java.awt
java.applet
java.io
java.net
java.sql
javax.swing
javax.sql
java.awt.event
and many more.

Here I will show a simple code to use javax.swing package.

In below program code we will use javax.swing package and will use some pre-existing code file.
Code: java

import javax.swing  // it should be the  line to import any package in your program code.
Class GuiApp
{
    JFrame f1;  // pre-existing code file named as JFrame javax.swing package
    JPanel p1; // pre-existing code file named as JPanel javax.swing package
    JLabel l1; // pre-existing code file named as JLabel in javax.swing package

    GuiApp() // creating a default constructor of our class
    {
        f1 = new JFrame("GUI APPLICATION"); // using JFrame class by calling its constructor.
        p1 = new JPanel();// using JPanel class by calling its default constructor.
        l1 = new JLabel("MANISH RANA"); // using JLable class by calling its constructor.

        f1.getContentPane().add(p1);
        f1.setSize(300,300);
        f1.setVisible(true);
        p1.add(l1);
    }
    public static void main(String s[])
    {
        GuiApp g = new GuiApp();
    }
}


Now in next example we will create our own package.
Code: java

package Hello;
class hel
{
    hel()
    {
        System.out.print("Hello Java");
    }
}

Now compile this code as you normally compile.

To compile this coed use the following command line code:

Part 1: To compile in same directory
javac –d .<filename>.java

Run using following command

java <package name>.<class file name>

Note you need to remove the <filename> by your own file name. In above Example its hel.java and package name is Hello.

Part 2: To other directory

javac –d <path>/<filename>.java

In this way you will be able to create your own package. Try some different types of code and use them in your code. And anytime you need help just drop a comment here.

shabbir 1Nov2010 16:27

Re: Packages - The Most Powerful Feature of Java
 
Nominate this article for Article of the month - Oct 2010 Before November 15th 2010

sbsl 27Sep2011 17:52

Re: Packages - The Most Powerful Feature of Java
 
good........thanks for sharing this, its good for beginners

puja2sharma 18Feb2012 13:10

Re: Packages - The Most Powerful Feature of Java
 
packages is used as object. we create the different packages for different purpose.

annasingh 10Jan2013 13:51

Re: Packages - The Most Powerful Feature of Java
 
thank you to given me great knowledge of packages


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