Question

Giving the following code snippet:

Discuss the reasons of using private access specifier in some places of the code and public in other places. Additionally, discuss how can you test this code.

public class Book

{

     privateStringbookName;

     privateinted;

     private String author;

    

     public Book (String n, int e, String a)

     {

           bookName = n;

           ed = e;

           author = a;

     }

    

     /**

     * Gets the book name.

     * @return the book name.

     */

     public String getBookName()

     {

           returnbookName;

     }

    

     /**

     * Gets the book edition.

     * @return the book edition.

     */

     publicintgetBookEd()

     {

           returned;

     }

    

     /**

     * Gets the book author.

     * @return the book author.

     */

     public String getAuthor()

     {

           return author;

     }

          

     /**

     * Prints the Book details.

     */

     public void printBookDetails()

     {

           System.out.println("Book Name:" + getBookName() );

           System.out.println("Book edition: " + getBookEd() );

           System.out.println("Book Author: " + getAuthor() );

     }

}

* use MS Format

* be sure of answer

Answer 1

Access modifiers in java defines the scope of the members of the class . This is used for data abstraction , so that functions from outside the class cannot get access to the one inside a class .

there are basically for types of access modifiers

• default : when we don't use any modifier its the default modifier . a class members which has a default modifier can be accessed in the same package , but if we try to access it from outside the package we will get a compile time error
• private : private members can be accesses within same class only in which they are present  ,i. e only the other members of the class can access private members , if we try to access them from outside the class we will get a compile time error .in our case our three variables are private so we shouldn't be able to access them outside the class . now this is done when we don't want other part of programs to access the data directly or affect in in some way .
• protected : now these members can be either accessed by all the classes that are present in the package in which the member is , or by the sub classes which are present in different package , they are used to extend the scope of data abstraction with inheritance  
• public :public methods can be called from anywhere . they have no limitation , in our case the other function including the constructor are public and can be called form any where

now since we understand the basic types of modifier lets try testing the program , i am assuming here we need to test the working of the access modifiers

1. lets first see the working of the public members , that is they can be called from outside the class

class Book

{

private String bookName;

private int ed;

private String author;

  

public Book (String n, int e, String a)

{

bookName = n;

ed = e;

author = a;

}

  

/**

* Gets the book name.

* @return the book name.

*/

public String getBookName()

{

return bookName;

}

  

/**

* Gets the book edition.

* @return the book edition.

*/

public int getBookEd()

{

return ed;

}

  

/**

* Gets the book author.

* @return the book author.

*/

public String getAuthor()

{

return author;

}

  

/**

* Prints the Book details.

*/

public void printBookDetails()

{

System.out.println("Book Name:" + getBookName() );

System.out.println("Book edition: " + getBookEd() );

System.out.println("Book Author: " + getAuthor() );

}

}

public class test{
/* lets test the access modifiers */
  
public static void main(String args[]){

/* now lets call the consructor which is public or otherwose we wont be able to call it */

   Book book_1 = new Book("50 shades of grey " , 5 ,"xyz");
  
  
   /*Calling the other public functions of the class */
  
  
  
   String b = book_1.getBookName();
   System.out.println("Book Name:" + b );
  
   int c = book_1.getBookEd();
   System.out.println("Book edition: " + c );
  
   String d = book_1.getAuthor();
   System.out.println("Book Author: " + d);
  
  
   System.out.println(" ");
  
   book_1.printBookDetails();

}
}

The output of the following program is :

and this is what we were expecting that we will be able to call the function .

2 . now for the private access modifier : we have kept some of our data private so that malicious codes cannot access or modify out data directly so lest test whether we can access those variables from outside and we are expecting a compile time error

class Book

{

private String bookName;

private int ed;

private String author;

  

public Book (String n, int e, String a)

{

bookName = n;

ed = e;

author = a;

}

  

/**

* Gets the book name.

* @return the book name.

*/

public String getBookName()

{

return bookName;

}

  

/**

* Gets the book edition.

* @return the book edition.

*/

public int getBookEd()

{

return ed;

}

  

/**

* Gets the book author.

* @return the book author.

*/

public String getAuthor()

{

return author;

}

  

/**

* Prints the Book details.

*/

public void printBookDetails()

{

System.out.println("Book Name:" + getBookName() );

System.out.println("Book edition: " + getBookEd() );

System.out.println("Book Author: " + getAuthor() );

}

}

public class test{
/* lets test the access modifiers */
  
public static void main(String args[]){

/* now lets call the consructor which is public or otherwose we wont be able to call it */

   Book book_1 = new Book("50 shades of grey " , 5 ,"xyz");
  
     book_1.printBookDetails();
  
  
  
   /* lets try calling some private members of class and lets see what we see on the compiler */
  
  
  
   System.out.println(book_1.bookName);
  
   System.out.println(book_1.ed);
  
  
   System.out.println(book_1.author);
  
  
  
  

}
}

the output of this code is :

so each time we called a private member we got a compile time error