package concepts in java class room discussions

Mr ramu dayinaboyina                                                                                       

package complex;

 public class c //here remove the public because we are saving this total as cominside.java   but public is allowed if save this file separately like c.java

{

int r,i;

public c(){}

public c(int r1,int i1)

{r=r1;

i=i1;}

public void add(c c1,c c2)

{r=c1.r+c2.r;

i=c1.i+c2.i;}

public void view()

{System.out.println(r+"+i"+i);}}

//here now need to write the import statement

class cominside

{

public static void main(String args[])

{

c a=new c(3,2);

c b=new c(1,2);

a.view();

b.view();

c cr=new c();

cr.add(a,b);

cr.view();

}

}

Case-1 package class and main method class in a single file sineraio like below

 

In the above I am putting  the main method class with  the package class file  itself  in the above code I am going to store the entire file with name cominside.java instead of separately saving c.java and cominside.java we know that if we have more than

 one class in a single java file with what name  we are going to save that class only allowed to declare as public

we are saving with the main method class this class only allowed to declare as public but not the class name with c

E:\jit\complex>dir      Volume in drive E is New Volume    Volume Serial Number is 003D-F678

 Directory of E:\jit\complex

21-Mar-12  12:32 AM               822 c.class

21-Mar-12  12:54 AM               406 cominside.java

               2 File(s)          1,228 bytes

               E:\jit\complex>javac cominside.java

cominside.java:2: class c is public, should be declared in a file named c.java

public class c

       ^       1 error

E:\jit\complex>javac cominside.java

E:\jit\complex>java cominside    //execuation is not allowed here but it will allows the compilation to get it compiled u go back to its parent directory from there u call package name .classname otherwise u get the below exception

Exception in thread "main" java.lang.NoClassDefFoundError:cominside

E:\jit\complex>cd..

E:\jit>java complex.cominside  //you must get back to the package parent directory then interpret the main class execution

3+i2

1+i2

4+i4

Case-2 package class is in separate folder and its calling class in the just above one level I.e. in the parent directory the scenario lie the below  

 

U define c.java file with package statement package complex u can compile this  2 ways one is

If u saved the above file e:\jit> in this location

Then   give the below command e:\jit>javac –d . c.java

Then in the e:\jit> another folder is created with name complex folder and it contains c.class file

After compilation u immediately remove the c.java source file from the location e:\jit> and in this location implement the main method class with the import statement

The other one is

First create manually folder with the package name what u wrote in the package class  then compile inside the package folder itself like below

e:\jit>md complex

e:\jit>cd complex

 e:\jit\complex>javac c.java

Here only compilation allowed here but not the interpretation

Note c.java u are allowed put the class name  as public  and  the main method class  allowed to put once again public u must save with respective class names as their filenames u  must use the explicit import statement in the main method class  

For the execution come out from the package folder cd..

e:\jit>javac  cominside.java  directly u are allowed to execute

e:\jit>java cominside

Total package implementation screen shot :-     

C:\Users\ramu>set classpath=%classpath%;e:\jit;.

I:\>dir s*.java    Directory of I:\

21-Mar-12  09:15 PM               146 samepack.java

               1 File(s)            146 bytes

I:\>javac samepack.java

I:\>java samepack

I AM INSIDE THE BASE CLASS CONSTRUCTOR