Why we put arraylist before public static void main(string[] args)

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why we put arraylist before public static void main(String[] args)

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package library;

/**
 *
 * @author maryam
 */
import java.util.Scanner;
import java.util.ArrayList;


public class LibraryDriver {
static ArrayList<Student> studentList=new ArrayList<Student>();
static ArrayList<Faculty> FacultyList=new ArrayList<Faculty>();
static ArrayList<Book> bookList=new ArrayList<Book>();
static ArrayList<Book> borroeList=new ArrayList<Book>();
   public static void main(String[] args)    {
       Scanner br = new Scanner(System.in);
       int reapeat=13;
       while(reapeat>0) {
           System.out.println("------------------------------------------------------");
           System.out.println("-------WELCOME TO OUR LIBRARY MANAGEMENT SYSTEM-------");
           System.out.println("------------------------------------------------------");
           System.out.println("----------Please choose one of below Options----------");
           System.out.println("1. Add Student");
           System.out.println("2. Add Faculty");
           System.out.println("3. Add Book");
           System.out.println("4. Display All Students");
           System.out.println("5. Display All Faculty");
           System.out.println("6. Display All Books");
           System.out.println("7. Search Student");
           System.out.println("8. Search Faculty");
           System.out.println("9. Search Book");
           System.out.println("10. Borow Book");
           System.out.println("11. Display All Borow Book");
           System.out.println("12. Return Book");
           System.out.println("13. Exit");
           System.out.print("your choice: ");
           int option = br.nextInt();
           System.out.println("------------------------------------------------------");
           switch (option) {
               case 1:
                   System.out.println("Enter Student Id");
                   int id = br.nextInt();
                   boolean chekId=checkStudentId(id);
                   if(chekId) {
                       System.out.println("StudentId Already Exist");
                       break;
                   }
                   br.nextLine();
                   System.out.println("Enter Student FirstName");
                   String surname= br.nextLine();
                   System.out.println("Enter Student lastName");
                   String lastName= br.nextLine();
                   System.out.println("Enter Student Age");
                   int age = br.nextInt();
                   Student student=new Student(id, surname, lastName, age);
                   studentList.add(student);
                   break;
               case 2:
                   System.out.println("Enter Faculty Id");
                   int id1 = br.nextInt();
                   boolean chekId1=checkFacultyId(id1);
                   if(chekId1) {
                       System.out.println("FacultyId Already Exist");
                       break;
                   }
                   br.nextLine();
                   System.out.println("Enter Faculty FirstName");
                   String surname1= br.nextLine();
                   System.out.println("Enter Faculty lastName");
                   String lastName1= br.nextLine();
                   System.out.println("Enter Faculty Age");
                   int age1 = br.nextInt();
                   Faculty Faculty=new Faculty(id1, surname1, lastName1, age1);
                   FacultyList.add(Faculty);
                   break;    
               case 3:
               System.out.println("Enter Book Id :");
               int bookId = br.nextInt();
               boolean chekBookId=checkBookId(bookId);
               if(chekBookId) {
                   System.out.println("Book Id Already Exist");
                   break;
               }
               br.nextLine();
               System.out.println("Enter Book tittle");
               String tittle= br.nextLine();
               System.out.println("Enter author FirstName");
               String authorSurname= br.nextLine();
               System.out.println("Enter author lastName");
               String authorName= br.nextLine();
               System.out.println("Enter Book Purchase Date");
               String purchaseDate= br.nextLine();
               System.out.println("Enter Book Availability :");
               String status= br.nextLine();
               Book b=new Book(bookId, tittle, authorSurname, authorName, purchaseDate, status)  {} ; // to implement all abrstract method
               bookList.add(b);
           break;
               case 4:
                   displayAllStudent();
                   break;
               case 5:
                   displayAllFaculty();
                   break;
               case 6:
                   displayAllBook();
                   break;
               case 7:
                   System.out.println("Please Enter student Id, you want to Search");
                   int searchStudentId = br.nextInt();
                   searchStudent(searchStudentId);
                   break;
               case 8:
                   System.out.println("Please Enter Faculty Id, you want to Search");
                   int searchFacultyId = br.nextInt();
                   searchFaculty(searchFacultyId);
                   break;
               case 9:
                   System.out.println("Please Enter Book Id, you want to Search");
                   int searchBookId = br.nextInt();
                   searchBook(searchBookId);
                   break;
               case 10:
                  borrowBook();
                   break;
               case 11:
                   DisplayborrowBook();
                   break;
               case 12:
                   returnBook();
                   break;
               case 13:
                   reapeat=-13;
                   break;
            }   
       }
   }
   private static void returnBook()  {
       Scanner br = new Scanner(System.in);
       try{
       System.out.println("---------------------");
       System.out.println("Please enter Student/Faculty Id:");
       int id = br.nextInt();
       System.out.println("Please enter Book Id:");
       int bookId = br.nextInt();
       for(int i=0; i<borroeList.size(); i++) {
               if(borroeList.get(i).getBookId()==bookId){
                      
                   borroeList.get(i).setStatus("AVAILABLE");
                   borroeList.remove(i);
                   break;
               }
           }
         
      } catch (NumberFormatException e) {
       System.err.println("error. " + e);
        }
   }
   private static void DisplayborrowBook() {
       for(Book book :borroeList) {
               System.out.println("Book Id:  "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
       }
   }
   private static void borrowBook() {
       Scanner br = new Scanner(System.in);
       System.out.println("----List of all Available book as Below----");
       for(Book book :bookList) {
           if(book.getStatus().equalsIgnoreCase("AVAILABLE")) {
               System.out.println("Book Id: "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
           }
       }
         System.out.println("---------------------");
       System.out.println("Please enter Student/Faculty Id:");
       int id = br.nextInt();
       System.out.println("Please enter Book Id:");
       int bookId = br.nextInt();
       for(Book book :bookList) {
               if(book.getBookId()==bookId){
                       borroeList.add(book);
                       book.setStatus("Not AVAILABLE");
               }
           }
   }
   private static void searchBook(int searchBookId) {
       boolean search=true;
       for(Book book :bookList) {
           if(book.getBookId()==searchBookId) {
               System.out.println("Book Id: "+book.getBookId()+" Tittle : "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
               search=false;
           }
          
       }
       if(search) {
           System.out.println(searchBookId+" Not exist");
       }
   }
   private static void searchStudent(int searchStudentId) {
       boolean search=true;
       for(Student st :studentList) {
           if(st.getStudentId()==searchStudentId) {
               System.out.println("Student Id: "+st.getStudentId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                       "Age: "+st.getAge());
               search=false;
           }
          
       }
      
       if(search) {
           System.out.println(searchStudentId+" Not exist");
       }
      
   }
   private static void displayAllBook() {
       for(Book book :bookList) {
           System.out.println("Book Id: "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                   " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
       }
      
   }
   private static void displayAllStudent() {
       for(Student st :studentList) {
           System.out.println("Student Id: "+st.getStudentId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                   "Age: "+st.getAge());
       }
      
   }
   private static boolean checkBookId(int bookId) {
       for(Book book: bookList) {
           if(book.getBookId()==bookId) {
               return true;
           }
       }
       return false;
   }
   private static boolean checkStudentId(int id) {
       for(Student st :studentList) {
           if(st.getStudentId()==id) {
               return true;
           }
       }
       return false;
   }
      private static boolean checkFacultyId(int id) {
       for(Faculty st :FacultyList) {
           if(st.getFacultyId()==id) {
               return true;
           }
       }
       return false;}
      private static void displayAllFaculty() {
       for(Faculty st :FacultyList) {
           System.out.println("Faculty Id: "+st.getFacultyId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                   "Age: "+st.getAge());
       }
      
   }
         private static void searchFaculty(int searchFacultyId) {
       boolean search=true;
       for(Faculty st :FacultyList) {
           if(st.getFacultyId()==searchFacultyId) {
               System.out.println("Faculty Id: "+st.getFacultyId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                       "Age: "+st.getAge());
               search=false;
           }
          
       }
      
       if(search) {
           System.out.println(searchFacultyId+" Not exist");
       }
      
   }
   }

What I have tried:

why we put arraylist before public static void main(String[] args)

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package library;

/**
 *
 * @author maryam
 */
import java.util.Scanner;
import java.util.ArrayList;


public class LibraryDriver {
static ArrayList<Student> studentList=new ArrayList<Student>();
static ArrayList<Faculty> FacultyList=new ArrayList<Faculty>();
static ArrayList<Book> bookList=new ArrayList<Book>();
static ArrayList<Book> borroeList=new ArrayList<Book>();
   public static void main(String[] args)    {
       Scanner br = new Scanner(System.in);
       int reapeat=13;
       while(reapeat>0) {
           System.out.println("------------------------------------------------------");
           System.out.println("-------WELCOME TO OUR LIBRARY MANAGEMENT SYSTEM-------");
           System.out.println("------------------------------------------------------");
           System.out.println("----------Please choose one of below Options----------");
           System.out.println("1. Add Student");
           System.out.println("2. Add Faculty");
           System.out.println("3. Add Book");
           System.out.println("4. Display All Students");
           System.out.println("5. Display All Faculty");
           System.out.println("6. Display All Books");
           System.out.println("7. Search Student");
           System.out.println("8. Search Faculty");
           System.out.println("9. Search Book");
           System.out.println("10. Borow Book");
           System.out.println("11. Display All Borow Book");
           System.out.println("12. Return Book");
           System.out.println("13. Exit");
           System.out.print("your choice: ");
           int option = br.nextInt();
           System.out.println("------------------------------------------------------");
           switch (option) {
               case 1:
                   System.out.println("Enter Student Id");
                   int id = br.nextInt();
                   boolean chekId=checkStudentId(id);
                   if(chekId) {
                       System.out.println("StudentId Already Exist");
                       break;
                   }
                   br.nextLine();
                   System.out.println("Enter Student FirstName");
                   String surname= br.nextLine();
                   System.out.println("Enter Student lastName");
                   String lastName= br.nextLine();
                   System.out.println("Enter Student Age");
                   int age = br.nextInt();
                   Student student=new Student(id, surname, lastName, age);
                   studentList.add(student);
                   break;
               case 2:
                   System.out.println("Enter Faculty Id");
                   int id1 = br.nextInt();
                   boolean chekId1=checkFacultyId(id1);
                   if(chekId1) {
                       System.out.println("FacultyId Already Exist");
                       break;
                   }
                   br.nextLine();
                   System.out.println("Enter Faculty FirstName");
                   String surname1= br.nextLine();
                   System.out.println("Enter Faculty lastName");
                   String lastName1= br.nextLine();
                   System.out.println("Enter Faculty Age");
                   int age1 = br.nextInt();
                   Faculty Faculty=new Faculty(id1, surname1, lastName1, age1);
                   FacultyList.add(Faculty);
                   break;    
               case 3:
               System.out.println("Enter Book Id :");
               int bookId = br.nextInt();
               boolean chekBookId=checkBookId(bookId);
               if(chekBookId) {
                   System.out.println("Book Id Already Exist");
                   break;
               }
               br.nextLine();
               System.out.println("Enter Book tittle");
               String tittle= br.nextLine();
               System.out.println("Enter author FirstName");
               String authorSurname= br.nextLine();
               System.out.println("Enter author lastName");
               String authorName= br.nextLine();
               System.out.println("Enter Book Purchase Date");
               String purchaseDate= br.nextLine();
               System.out.println("Enter Book Availability :");
               String status= br.nextLine();
               Book b=new Book(bookId, tittle, authorSurname, authorName, purchaseDate, status)  {} ; // to implement all abrstract method
               bookList.add(b);
           break;
               case 4:
                   displayAllStudent();
                   break;
               case 5:
                   displayAllFaculty();
                   break;
               case 6:
                   displayAllBook();
                   break;
               case 7:
                   System.out.println("Please Enter student Id, you want to Search");
                   int searchStudentId = br.nextInt();
                   searchStudent(searchStudentId);
                   break;
               case 8:
                   System.out.println("Please Enter Faculty Id, you want to Search");
                   int searchFacultyId = br.nextInt();
                   searchFaculty(searchFacultyId);
                   break;
               case 9:
                   System.out.println("Please Enter Book Id, you want to Search");
                   int searchBookId = br.nextInt();
                   searchBook(searchBookId);
                   break;
               case 10:
                  borrowBook();
                   break;
               case 11:
                   DisplayborrowBook();
                   break;
               case 12:
                   returnBook();
                   break;
               case 13:
                   reapeat=-13;
                   break;
            }   
       }
   }
   private static void returnBook()  {
       Scanner br = new Scanner(System.in);
       try{
       System.out.println("---------------------");
       System.out.println("Please enter Student/Faculty Id:");
       int id = br.nextInt();
       System.out.println("Please enter Book Id:");
       int bookId = br.nextInt();
       for(int i=0; i<borroeList.size(); i++) {
               if(borroeList.get(i).getBookId()==bookId){
                      
                   borroeList.get(i).setStatus("AVAILABLE");
                   borroeList.remove(i);
                   break;
               }
           }
         
      } catch (NumberFormatException e) {
       System.err.println("error. " + e);
        }
   }
   private static void DisplayborrowBook() {
       for(Book book :borroeList) {
               System.out.println("Book Id:  "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
       }
   }
   private static void borrowBook() {
       Scanner br = new Scanner(System.in);
       System.out.println("----List of all Available book as Below----");
       for(Book book :bookList) {
           if(book.getStatus().equalsIgnoreCase("AVAILABLE")) {
               System.out.println("Book Id: "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
           }
       }
         System.out.println("---------------------");
       System.out.println("Please enter Student/Faculty Id:");
       int id = br.nextInt();
       System.out.println("Please enter Book Id:");
       int bookId = br.nextInt();
       for(Book book :bookList) {
               if(book.getBookId()==bookId){
                       borroeList.add(book);
                       book.setStatus("Not AVAILABLE");
               }
           }
   }
   private static void searchBook(int searchBookId) {
       boolean search=true;
       for(Book book :bookList) {
           if(book.getBookId()==searchBookId) {
               System.out.println("Book Id: "+book.getBookId()+" Tittle : "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                       " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
               search=false;
           }
          
       }
       if(search) {
           System.out.println(searchBookId+" Not exist");
       }
   }
   private static void searchStudent(int searchStudentId) {
       boolean search=true;
       for(Student st :studentList) {
           if(st.getStudentId()==searchStudentId) {
               System.out.println("Student Id: "+st.getStudentId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                       "Age: "+st.getAge());
               search=false;
           }
          
       }
      
       if(search) {
           System.out.println(searchStudentId+" Not exist");
       }
      
   }
   private static void displayAllBook() {
       for(Book book :bookList) {
           System.out.println("Book Id: "+book.getBookId()+" Tittle: "+book.getTittle()+" Auhtor Surname: "+book.getAuthorSurname()+
                   " Author FirstName: "+book.getAuthorFirsName()+" Purchase Date: "+book.getPurchaseDate()+" staus: "+book.getStatus());
       }
      
   }
   private static void displayAllStudent() {
       for(Student st :studentList) {
           System.out.println("Student Id: "+st.getStudentId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                   "Age: "+st.getAge());
       }
      
   }
   private static boolean checkBookId(int bookId) {
       for(Book book: bookList) {
           if(book.getBookId()==bookId) {
               return true;
           }
       }
       return false;
   }
   private static boolean checkStudentId(int id) {
       for(Student st :studentList) {
           if(st.getStudentId()==id) {
               return true;
           }
       }
       return false;
   }
      private static boolean checkFacultyId(int id) {
       for(Faculty st :FacultyList) {
           if(st.getFacultyId()==id) {
               return true;
           }
       }
       return false;}
      private static void displayAllFaculty() {
       for(Faculty st :FacultyList) {
           System.out.println("Faculty Id: "+st.getFacultyId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                   "Age: "+st.getAge());
       }
      
   }
         private static void searchFaculty(int searchFacultyId) {
       boolean search=true;
       for(Faculty st :FacultyList) {
           if(st.getFacultyId()==searchFacultyId) {
               System.out.println("Faculty Id: "+st.getFacultyId()+" FirstName: "+st.getSurname()+" lastName: "+st.getLastName()+
                       "Age: "+st.getAge());
               search=false;
           }
          
       }
      
       if(search) {
           System.out.println(searchFacultyId+" Not exist");
       }
      
   }
   }

Posted 27-Apr-21 9:18am

Member 14999822

Updated 27-Apr-21 9:35am

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OriginalGriff · Answer 1 · 2021-04-27T09:35:00

Solution 1

Because they are static variables which are available to every method in the class (and if declared as public to methods outside the class as well).

If you declare a variable inside a method it is called a local variable and is only available inside the method, then destroyed when the method exits.

Posted 27-Apr-21 9:35am

OriginalGriff

Comments

Member 14999822 27-Apr-21 15:43pm

can you explain more?

OriginalGriff 27-Apr-21 15:47pm

About what?