如何将用户输入存储到数组列表中？

Question

I am writing a program that allows the user to input the details of a book and store them in an Array List. My question is, how can I get the code I am using to store more than one value in my array list instead of just overwriting what's already there?

Here's what I have so far...

Scanner input = new Scanner(System.in);
    System.out.println("What is the book called?..");
    String bTitle = input.nextLine();
    System.out.println("Who is the author?..");
    String bAuthor = input.nextLine();
    System.out.println("How many do you have?..");
    int bQuantity = input.nextInt();
    System.out.println("How many are out on loan?..");
    int bNumOnLoan = input.nextInt();
    System.out.println("How many times has it been loaned?..");
    int bNumTimesLoaned = input.nextInt();

    ArrayList<Book> books = new ArrayList<Book>();
    Book object = new Book(bTitle, bAuthor, bQuantity, bNumOnLoan, bNumTimesLoaned);
    books.add(object);

But when I run this again the values that I entered before have been replaced. Any help would be most appreciated as I am stumped.

Answer 1

import java.util.ArrayList;
import java.util.Scanner;

public class BookCapture {

     static ArrayList<Book> books = new ArrayList<Book>();

    public static void main(String ase[]){

        for(int i=0;i<5;i++){
            capture();
        }
       System.out.println(books.toArray());
    }

    public static void capture(){
        Scanner input = new Scanner(System.in);
        System.out.println("What is the book called?..");
        String bTitle = input.nextLine();
        System.out.println("Who is the author?..");
        String bAuthor = input.nextLine();
        System.out.println("How many do you have?..");
        int bQuantity = input.nextInt();
        System.out.println("How many are out on loan?..");
        int bNumOnLoan = input.nextInt();
        System.out.println("How many times has it been loaned?..");
        int bNumTimesLoaned = input.nextInt();

        Book object = new Book(bTitle, bAuthor, bQuantity, bNumOnLoan, bNumTimesLoaned);
        books.add(object);
    }
}
class Book{
    // your book class
    // do override your tostring() method;
}

In the above code you are requesting the user to enter the details 5 times and this gets captured in the books ArrayList object. The for loop can be modified to make it more user friendly by asking he want to enter more book.

For example modify the above code to ask the user the following way.

Press 1: if you wish to add another book

Press 2: If you wish to view all the books

Press 3: If you wish to quit the program.

Further assignment.

Read a little about serialization.This will solve the problem of having the data stored in between runs.Then,modify the program to additionally do the following.

Press 4: If you wish to quit with books stored.

Press 5: If you wish to retrieved all archived books :)

Answer 2

Using .add() doesn't replace what is inside the ArrayList, it only adds a new element to the list.

That means to add more than one item, just use .add() multiple times.

Then you could get these items using their indices, for example:

ArrayList<String> list = new ArrayList<String>();
list.add("item1");
list.add("item2");

In order to get 'item1', use list.get(0) , and to get 'item2', use list.get(1) .

---

Also, Java will not save variable data between runs . When a program ends, all the data stored inside any variables will be lost .

To save the data between runs, you could save the data to a file and read the data from it at the start of the run. Look into using a FileWriter and FileReader .