Mumbai University > Information Technology > Sem 3 > Object Oriented Programming Methodology

Marks: 5 M

Year: May 2014, Dec 2014, May 2015

• A package is called as the collection of classes and interfaces.
• A Java package is simply a directory that contains one or more class files. It is, therefore, just a matter of:
• Creating a folder
• Moving the class file to the new folder (or creating them there)
• Calling the package from any applications
• The first step is to create the directory for the package. This can go in one of two places:
• In the same folder as the application that will be using it
• In a location listed in the system CLASSPATH environmental variable
• So, for example, if CLASSPATH contains C:\Java\Packages then the new package can be created there, for example C:\Java\Packages\suite101, and once the directory has been created then classes can be added to it.

• Next step is to create a class, Java source file. The first line of a class in a package is essential - it must contain the name of the package:

  package suite101;

• No code is allowed above the package statement, but after that critical line the class can be defined as normal. For example it can call any packages that it requires:

  import java.util.* ;

  import java.text.* ;

• In this example the class contains a single method which returns today's date formatted for the current locale:

  public class formatted_date 
  {
  public static String today ()
  {
  Date mydate = new Date();
  String dateString =DateFormat.getDateInstance().format(mydate);
  return dateString;
  }
  }
  

• As always the code must be saved to a text file with the same name as the class - in this case that's C:\Java\Packages\suite101\formatted_date.java.

• Now, we can use the above created java package in any program by import statement:

  import suite101.* ;

• This will load any classes found in the suite101 directory. The formatted_date class can now be used in the class for the new application.

   public class use_packages 
   {
   public static void main(String args[])
   {
  formatted_date newday = new formatted_date();
  System.out.println(newday.today());
  }
  }
  

• The above code makes use of formatted_date class by importing suite101 package.