Question

我是java的新手，对不一致感到抱歉。

我正在创建一个库程序，我在Patron类的Book类中调用方法时遇到了麻烦。

在Patron课程中，我有一个方法checkOutBook（），用户可以输入一本书来检查。但是我在Book中访问setStatus（）方法时遇到了问题。我知道我必须针对Book类的实例调用它，但我不确定如何使用用户输入的字符串。

function getFreeCode(callback) {
    var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    var code = "";
    for (var i = 0; i < 4; i++) {
      var rand = Math.floor(Math.random() * chars.length);
      console.log(rand);
      code += chars.charAt(rand);
    }
    console.log("Code: %s generated.", code);

    client.execute("select * from codes where code="+code, function(err, result) {
      if(!err) {
        if(result.rows.length > 0) {
          getFreeCode(callback);
        } else {
          callback(code);
        }
      }else {
        console.log('DB ERR: %s', err);
      }
      console.log(codeFree);
    });
    console.log('here');
}




// in your main:

getFreeCode(function (code) {
    console.log(' this code was free: ' + code)
})

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

public class Book implements BookInterface {

  Scanner input = new Scanner(System.in);
  static ArrayList < String > UserList = new ArrayList < String > ();
  static ArrayList < String > BookList = new ArrayList < String > ();

  public String title;
  public String author;
  public Book book;
  private String status;
  private String borrower;

  public Book(String t, String a) {
    title = t;
    author = a;
  }

  //constructor create new book
  public Book(String newTitle) {
    title = newTitle;
  }


  public String toString() {
    return title + " " + author;
  }

  public String getTitle() {
    return title;
  }

  public void setTitle(String title) {
    this.title = title;
  }

  public String getAuthor() {
    return author;
  }

  public void setAuthor(String author) {
    this.author = author;
  }

  public String getStatus(String book) {
    return status;
  }

  public void setStatus(String status) {
    this.status = status;
  }

  public void setBorrower(String borrower) {
    this.borrower = borrower;
  }

  public String getBorrower(String checkPatron) {
    return borrower;
  }

  public String getBook(String checkPatron) {
    return book;
  }

  public void setBook(Book bookCheckOut) {
    this.book = bookCheckOut;
  }


}

我试图这样做，但它也不起作用:( 谢谢您的帮助！

public void CheckOutBook() {
    Scanner inputread = new Scanner(System.in);
    Scanner input = new Scanner(System.in);
    System.out.println("Enter full patron name: ");
    String borrower = inputread.nextLine();
    System.out.println("Enter book title to check out: ");
    String bookCheckOut = inputread.nextLine();

    if (Book.BookList.contains(bookCheckOut)) {
      Book.BookList.remove(bookCheckOut);
      Book.setStatus("OUT");      //error message        
      Book.setBorrower(borrower);  //error message 
      System.out.println("----------" + bookCheckOut + " has been checked out!----------");
      System.out.println("-------------------BOOK STATUS:---------------------");
      System.out.println("Book Title: " + bookCheckOut);
      System.out.println("Book Status: Checked out");
      System.out.println("Borrower: " + borrower);
      System.out.println("Due Date: " + dueDate);
      System.out.println("----------------------------------------------------");

Answer 1

Book bookCheckOut = new Book（bookCheckOut）; ＆lt;〜我认为你很困惑，因为你已经将bookCheckOut定义为扫描仪中的一个字符串，在这一行中你将它设置为一个书本对象。尝试将此行中的第一个bookCheckOut更改为其他内容。语法：Book bookObjectName = new Book（“String”）;

对于setStatus和setBorrower错误，您尝试使用这些方法，就好像它们是静态的一样。要解决此问题，请不要调用Book.setStatus，而是将Book替换为您实例化的book对象名称。示例：预订b =新书（“Asd”，“abc”）; b.setStatus（ “XYZ”）;

另外，为什么要有两台扫描仪？

Answer 2

将Book.BookList从ArrayList<String>更改为Map<String, Book>，如下所示：

public class Book {

  static Map<String, Book> BookList = new HashMap<>();

  ...

然后在CheckOutBook()更改：

if (Book.BookList.contains(bookCheckOut)) {
  Book.BookList.remove(bookCheckOut);
  Book.setStatus("OUT");      //error message        
  Book.setBorrower(borrower);  //error message 

  ...

要：

Book book = Book.BookList.get(bookCheckOut);
if (book != null) {
  Book.BookList.remove(bookCheckOut);
  book.setStatus("OUT");     
  book.setBorrower(borrower);

  ...

从类的实例调用方法

2 个答案: