java - 代码中的扫描仪错误，使用引用变量构建数组

Question

我对编码还很陌生，所以如果有明显的修复，我深表歉意。

我正在尝试构建一个可以存储书籍对象的库，但在我可以使用功能之前，我需要整理一个数组。 Java 本身在我的侧栏中没有显示任何错误，但是当通过控制台运行时，会出现错误。

下面我发布了我的 Library.java 类。

import java.util.Scanner;


public class Library {
	
	public static void main(String[] args){
		
		Scanner input = new Scanner(System.in);
		
		Book[] books = new Book[2];
		String Title;
		String Author;
	    String BookID;
		Boolean onLoan;
		int NumberofLoans;
		
		for( int i = 0; i < books.length; i++){
			System.out.print("Enter the title of the book: ");
			Title = input.next();
			books[i] = new Book();
			books[i].setTitle(Title);
			System.out.println("");
			
			System.out.print("Enter the Author of the book: ");
			Author = input.next();
			books[i].setAuthor(Author);
			System.out.println("");
			
			System.out.print("Enter the Book's ID: ");
			BookID = input.next();
			books[i].setBookID(BookID);
			System.out.println("");
			
			NumberofLoans = 0;
			books[i].setNumberofLoans(NumberofLoans);
			
			onLoan = false;
			books[i].setonLoan(onLoan);
			
			input.close();
			}
		
		for(int i = 0; i < books.length; i++){
			System.out.println("Title: " + books[i].getTitle());
			System.out.println("Author: " + books[i].getAuthor());
			System.out.println("BookID: " + books[i].getBookID());
			System.out.println("Times loaned: " + books[i].getNumberofLoans());
			System.out.println("In library: " + books[i].getonLoan());
			
		}	
	}
}

下面列出了控制台错误本身:

Exception in thread "main" Enter the title of the book:
java.lang.IllegalStateException: Scanner closed
at java.util.Scanner.ensureOpen(Scanner.java:1070)
at java.util.Scanner.next(Scanner.java:1358)
at Library.main(Library.java:19)

有人可以指出我的代码中的错误来自何处吗？那么，我可以进行更改来阻止此错误的发生吗？

为了确保列出所有内容，我将发布 Book.java，以防错误源自那里。

public class Book {

private String Title;
private String Author;
private String BookID;
private Boolean onLoan;
private int NumberofLoans;



public Book(){
    Title = new String();
    Author = new String();
    BookID = new String();
    onLoan = false;
    NumberofLoans = 0;

}

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

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

public void setBookID(String bookID) {
    this.BookID = bookID;
}

public void setonLoan(Boolean onLoan) {
    this.onLoan = onLoan;
}

public void setNumberofLoans(int numberofLoans) {
    this.NumberofLoans = numberofLoans;
}

public String getTitle() {
    return Title;
}

public String getAuthor() {
    return Author;
}

public String getBookID() {
    return BookID;
}

public Boolean getonLoan() {
    return onLoan;
}

public int getNumberofLoans() {
    return NumberofLoans;
}}

Answer 1

在Library类的第一个循环中导致了这种情况。具体来说，这一行:

input.close();

因为您在整个程序完全使用扫描仪之前就将其关闭。 Scanner 在循环第一次运行时可用。但第一次执行后，您关闭扫描仪。因此，对于连续的循环运行，扫描仪关闭，因此出现错误。

循环结束后添加此行。换句话说，像这样:

for( int i = 0; i < books.length; i++){
    // ... Whatever
}

input.close();