Q) Create and make use of a user defined package?

A)
->if syntax is correct, only then package is created.

->”-d” destination of ‘.class’ file is not in the current working directory but in the user defined package.

//E:\today\imp\a.java

Package mypack;

Public class a

{

  Void x()

     {

         System.out.println(‘x method”);

     }

}

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

//E:\today\imp\b.java

Package mypack;

Public class b

{

    public void y()

     {

         a A= new a();

         A.x();

        Syste.out.prinln(“y method”);

     }

}

Note:
package statement should be the first non comment statement in the compilation unit.

E:\today\imp>javac –d . * .java

->’imp’ directory, “mypack” package is created a.class and b.class files are grouped (stored) in mypack.

->before we use “mypack” set the classpath. Place the fallowing value in classpath environment variable.

E:\todat\imp (using ‘;’ separator) (never include user defined here)

->java application that uses the user defined package?
//E:\c.java

Import mypack .b;

Class c

{

    Public static void main(String args[])

      {

            b B=new b();

            B.y();

      }

}

Here ‘public’ keyword is used in A.java and b.java before class and before method because ‘imp’ is separate directory and ‘mypack’ is separate so to a access the classes and method outside the ‘imp’ directory we uses access specified.

Public:
package mypack;

Import java.util.*;

Public class b

{

    Public void y()

     {

         A A=nre a();

         a.x();

         Scanner s=new Scanner(System.in);

     }

}

->now we meet to include ‘Scanner’ class using util package use import statement but ‘import’ should be written after the package statement only.

->if import mypack.*; is given in the code ‘*’ – works only when from imp directory we have to remove ‘.java’ files only  ‘.class’ files should be there or else import separately.

->suppose if we are working for www.yourdomain.com then if it is having user, admin modules then you are creating package for user then package com. yourdomain.user(reverse domain naming conversation).