java - (图书馆) checkout 状态返回所有 "true"

Question

我没有使用 boolean 值来查看一本书是否被 checkout ，而是我想用一个字符串来表示它是我想要的，但是当我调用该方法来 checkout 一本书时，该字符串适用于书籍对象的整个数组列表。我怎样才能更改那本书的状态？

import java.util.*;

public class Library 
{

  String owner;
  int numBooks;
  boolean isCheckedOut;
  String status = "false";

  ArrayList<Book> bookList = new ArrayList<Book>();



public void addBook(Book b)
{
    bookList.add(b);

}
 public  String checkout(Book c) {

    status = "true";
    return status;

  }

  public Library(String o)
  {
    owner = o;
  }
  public String toString()
  {


   String s = "Owner:    \t" + owner + "\nSize:    \t" + 
               bookList.size()+"\nBooks:   \t";
   for( int i = 0;i < bookList.size();i++)
    { 
      String title = bookList.get(i).getTitle();
      //System.out.println(title);
      s+="\n\t\t\t" +title +"     Checked out: " + status;  //bookList.get(i).getStatus();
    }





    return s;
  }

  public static void main(String [] args)
  {
    Library l = new Library("Jeremiah");
    System.out.println(l);



  }
}

我

public class Mainn
{
  public static void main(String [] args)
  {
    Book book1  = new Book("Aambi","Aisney","Aalt","1942",1453);
    Book book2  = new Book("Bambi","Bisney","Balt","1942",1453);
    Book book3  = new Book("Cambi","Cisney","Calt","1942",1453);
    Book book4  = new Book("Dambi","Disney","Dalt","1942",1453);
    Book book5  = new Book("Eambi","Eisney","Ealt","1942",1453);
    Book book6  = new Book("Fambi","Fisney","Falt","1942",1453);
    Book book7  = new Book("Gambi","Gisney","Galt","1942",1453);
    Book book8  = new Book("Hambi","Hisney","Halt","1942",1453);
    Book book9  = new Book("Iambi","Iisney","Ialt","1942",1453);
    Book book10 = new Book("Jambi","Jisney","Jalt","1942",1453);
    Book book11 = new Book("Kambi","Kisney","Kalt","1942",1453);
    Library l = new Library("Jeremiah"); 

    // l.addBook(new Book("Xambi","Xisney","Xalt","1579",765)); 

     l.addBook(book1);
     l.addBook(book2);
     l.addBook(book3);
     l.addBook(book4);
     l.addBook(book5);
     l.addBook(book6);
     l.addBook(book7);
     l.addBook(book8);
     l.addBook(book9);
     l.addBook(book10);
     l.addBook(book11);


    // this changes all of the values to true  instead of just this one
     l.checkout(book1);
     l.checkout(book11);

     l.addBook(book1);

      System.out.println(l);
  }
}

Answer 1

您存储的是图书馆的状态，而不是每本书的状态。要 checkout 单本书，您需要将状态字段放入图书中，然后设置图书的状态:

public class Book
{
    public String status;
    // etc...
}

public String checkout(Book c) {
    c.status = "true";
    return c.status;
}

将 boolean 值存储为字符串通常不是最好的主意 - 通常最好为此使用实际的 boolean 字段。

更简洁(更面向对象)的实现看起来像这样:

public class Book {

    private boolean checkedOut = false;

    public void checkout() {
        checkedOut = true;
    }

    public void checkin() {
        checkedOut = false;
    }

    public boolean isCheckedOut() {
        return checkedOut;
    }
}

这保留了使用图书本身管理图书的逻辑，并允许您轻松添加验证，例如如果该字段已设置为 true，则阻止 checkout 。