Java 应用程序崩溃

Question

我用 Java 制作了一个简单的图书馆管理应用程序。当我运行它并输入一本书的标题时，例如“Java:如何编程”它崩溃了。但如果我只是输入“Java”而不是“Java:如何编程”，一切都会顺利进行。

出了什么问题？请帮忙。

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Scanner;

public class MainSystem {

static String fileName = null;
static Library lib = new Library();
static Scanner in = new Scanner(System.in);
static Boolean running = true;

public static void main(String[] args) {
    while (running) {
        System.out.println("\nEnter 0 for load a library."
                + "\nEnter 1 for save and quit"
                + "\nEnter 2 for list all books in library"
                + "\nEnter 3 for add book to library");

        int answer = in.nextInt();
        switch (answer) {
        case 0:
            System.out.println("Enter the file name to load");
            loadScript(in.next());
            break;

        case 1:
            saveAndQuit();
            break;
        case 2:
            System.out.println(lib.toString());
            break;
        case 3:
            addBook();
            break;
        }
    }
    System.exit(0);
}

private static void addBook() {
    // TODO Auto-generated method stub
    int isbn;
    String title, author;
    double price;

    System.out.println("\nEnter Title: ");
    title = in.next();

    System.out.println("\nEnter Author: ");
    author = in.next();

    System.out.println("\nEnter ISBN: ");
    isbn = in.nextInt();

    System.out.println("\nEnter Price: ");
    price = in.nextDouble();

    Book b = new Book(isbn, title, author, price);
    lib.addBook(b);
}

private static void saveAndQuit() {
    // TODO Auto-generated method stub
    System.out.println("Enter file name: ");
    fileName = in.next() + ".ser";
    running = false;
    FileOutputStream fos = null;
    ObjectOutputStream out = null;
    try {
        fos = new FileOutputStream(fileName);
        out = new ObjectOutputStream(fos);
        out.writeObject(lib);
        fos.close();
        out.close();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

private static void loadScript(String name) {
    // TODO Auto-generated method stub
    FileInputStream fis = null;
    ObjectInputStream in = null;
    File file = new File(name + ".ser");
    if (file.exists()) {
        try {
            fis = new FileInputStream(file);
            in = new ObjectInputStream(fis);
            lib = (Library) in.readObject();
            fis.close();
            in.close();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    } else {
        System.out.println("\nThe file does not exist!");
    }
}

}

Answer 1

当您想要/需要读取整行时，您正在读取下一个String。更改此:

in.next();

由

in.nextLine();

当询问您的图书数据时:

private static void addBook() {
    // TODO Auto-generated method stub
    int isbn;
    String title, author;
    double price;

    System.out.println("\nEnter Title: ");
    title = in.nextLine();

    System.out.println("\nEnter Author: ");
    author = in.nextLine();

    System.out.println("\nEnter ISBN: ");
    isbn = in.nextInt();

    System.out.println("\nEnter Price: ");
    price = in.nextDouble();

    Book b = new Book(isbn, title, author, price);
    lib.addBook(b);
}

<小时/>

来自评论:

When I change in.next to in.nextLine, while running the program Enter Title and Enter Author` appear simultaneously; instead first Enter Title should appear and after giving a Title Enter Author should appear

请注意，nextLine 将消耗所有输入，直到 Scanner 找到新的断线输入。这意味着您必须在读取书籍数据之前添加额外的 nextLine():

private static void addBook() {
    // TODO Auto-generated method stub
    int isbn;
    String title, author;
    double price;
    in.nextLine(); //consume the data...

    System.out.println("\nEnter Title: ");
    title = in.nextLine();

    System.out.println("\nEnter Author: ");
    author = in.nextLine();

    System.out.println("\nEnter ISBN: ");
    isbn = in.nextInt();

    System.out.println("\nEnter Price: ");
    price = in.nextDouble();

    Book b = new Book(isbn, title, author, price);
    lib.addBook(b);
}

更多信息:

Scanner.nextLine documentation