- public class Book { 
-   
-     private String author; 
-     private String title; 
-     private String refNumber; 
-     private int pages; 
-     
-     public Book(String bookAuthor, String bookTitle, String bookRefNumber, int bookPages) { 
-         author = bookAuthor; 
-         title = bookTitle; 
-         pages = bookPages; 
-         refNumber = ""; 
-     } 
-     
-     public String getAuthor() { 
-         return author; 
-     } 
-     public String getTitle() { 
-         return title; 
-     } 
-     
-     public int getPages() { 
-         return pages; 
-     } 
-     
-     public String getRefNumber() { 
-         return refNumber; 
-     } 
-     
-     public void setRefNumber(String refNumber) { 
-         String errMsg = "Reference Number harus diatas 3 karakter"; 
-         
-         if(refNumber.length()<3) { 
-             System.out.println(errMsg); 
-         } 
-         else { 
-             this.refNumber = refNumber; 
-         } 
-         
-             
-     } 
-     
-     public void printAuthor() { 
-         System.out.println(author); 
-     } 
-     
-     public void printTitle() { 
-         System.out.println(title); 
-     } 
-     
-     public void printDetails() { 
-         String refNumPrint = refNumber; 
-         
-         System.out.println("Title: " + title + ", Author: " + author + ", Pages: " + pages); 
-         
-         if(refNumPrint.length() < 0) { 
-             refNumPrint = "ZZZ"; 
-         } 
-         System.out.println("Reference number:  " + refNumPrint); 
-     } 
- }