从arrayList中删除对象并打印出剩余的对象

Question

i have a code that stores the number of books in arraylist, every time a book is borrowed the user is prompted to input a number starting from zero which represents the first book and 1 for the second and so on. it runs at first deleting the first object from the arraylist, then when it gets to the last, it throws an IndexOutOfBoundException, here's my block of code, please help!

  //class doesn't do much than just gets the title of the book
 public class BookLibrary {
  String title;

 public BookLibrary(){}

public void setTitle( String names) {
    title = names;
}

public String getTitle(){
    return title;
}
}

here's my code that deletes the object from the arraylist public class LibraryAssistant {

 ArrayList<BookLibrary> booklib = new ArrayList<>();
 int numOfBooks = 0;

 public void setupLibrary(){
    BookLibrary bc = new BookLibrary();
    bc.setTitle("fantastic beasts and where to find them");
    BookLibrary bc1 = new BookLibrary();
    bc1.setTitle("Harry potter and the prisoner of azkabans");
    BookLibrary bc2 = new BookLibrary();
    bc2.setTitle("one day for the thief");
    booklib.add(bc);
    booklib.add(bc1);
    booklib.add(bc2);
    numOfBooks++;

    for(BookLibrary book : booklib){
       System.out.println(book.getTitle());

    }
}

public void borrowbook(){
    while(!booklib.isEmpty()){
        String getbooknum = userInput("please enter a book number of the             book you want to borrow");
        int index = Integer.parseInt(getbooknum);
        if(index>=0){
            booklib.remove(index);
            for(BookLibrary lb : booklib){
                System.out.println(lb.getTitle());
            }
        }
        numOfBooks--;
    } if(booklib.isEmpty()){
        System.out.println("the library is empty");
    }
}

Answer 1

The reason behind the IndexOutOfBoundException is the size of arraylist gets decremented everytime you remove the object. so if you remove the first title (index 0) from the book the size of list will be 2. when user go for second removal (index 1), it will work fine. But when user will go for 3rd removal (index 2), it will throw IndexOutOfBoundException as the size of ArrayList is 1 now.

Answer 2

My first observation is that numOfBooks in setUpLibrary() should be set to 3. or should be updated as the size of the array list. The second observation is that in borrowbook(), while loop runs until the bookLib becomes empty. So line booklib.remove(index); will throw error IndexOutOfBoundsException when there are no more elements or the number given by the user is out of range.

Please refer below documentation: https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#remove(int)