CODEWITHSUNDEEP
javamethodsreturn-value
Mac
Mac

Reputation: 111

How to declare method return value?

Ok, i have this class Libray that uses another class named Book. I want to make a method that erase an object book in the array inventary, but i dont how to declare the return value of the method, i want to return the object libray to use it in another class, where i will display all the books in it. The num variable its given by the user in another class, its represents the number of the book to erase. The array inventary starts from 0 to 9.

public class Library {

 private Book[] inventary;
 private int     booksquantity;

 public Library eraseBook(int num){
    for(int i=0 ; i<booksquantity ; i++){
         if(i == num-1){
            for(int j = i ; j<booksquantity ; j++){
                inventary[j] = inventary[j+1];}
         }          
   }return ***;
 }  
}

//In the other class i would make something like this to use this method eraseBook, in a //switch

case 6: 
                    AppLibrary.cleanscreen();//Static method to erase the screen
                    System.out.println("What book do u wish to delete?");
                    String inventary = ghandi.generateInventory();//this makes the        //inventory to the user
                        if(inventary.equals("")){
                            System.out.println("No books available in the inventary");
                        }
                        else{
                            System.out.println(inventary);
                        }
                    int num = Integer.parseInt(s.nextLine());//here i read from the //keyboard the number of book the user wants to delete
//Here the object libary is caled "ghandi"
                    ghandi.eraseBook(num);//here i use the method
                    System.out.println("Book erase, please display inventary again");
                   s.nextLine();
                    break;

Thanks!!

Upvotes: 1

Views: 170

Answers (4)

Jeroen Vannevel
Jeroen Vannevel

Reputation: 44459

Use void if you don't want to return anything (which I assume is the case here).

If you want to return the object you're in (so, the current library that you just deleted from), use the this keyword.

Upvotes: 2

Arash Saidi
Arash Saidi

Reputation: 2238

You can use void as the method signature:

public void eraseBook(int num){}

Or you could return null at the end of method, but that is not a good practice.

Upvotes: 0

lilmessi42
lilmessi42

Reputation: 313

Use void if you do not want to return anything.

Upvotes: 0

Skylion
Skylion

Reputation: 2752

add a constructor Library(Book[] inventary, int booksquantity) and call it in the return method so.

public class Library {

 private Book[] inventary;
 private int     booksquantity;

 public Library(Book[] inventary, int booksquantity){
    this.inventary = inventary;
    this.booksquantity = booksquantity;
 }

 public Library eraseBook(int num){
    for(int i = 0; i<booksquantity ; i++){ 
       if((inventary[i] == inventary[num-1]) && (inventary[i+1] != null)){
           inventary[i+1]= inventary[i];
       } else if(inventary[i] == inventary[num-1]){
           inventary[i] = null;
       }
   } 
      return new Library(inventary, booksquantity);
 }  
}

if you just want to erase a book and not make the whole class immutable.

public class Library {

 private Book[] inventary;
 private int     booksquantity;

 public Library(Book[] inventary, int booksquantity){
    this.inventary = inventary;
    this.booksquantity = booksquantity;
 }

 public void eraseBook(int num){
    for(int i = 0; i<booksquantity ; i++){ 
       if((inventary[i] == inventary[num-1]) && (inventary[i+1] != null)){
           inventary[i+1]= inventary[i];
       } else if(inventary[i] == inventary[num-1]){
           inventary[i] = null;
       }
   } 
 }  
}

Upvotes: 0

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