Question

我用Java创建了一个简单的库管理应用程序。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。但是，如果我只输入“Java”而不是“Java：如何编程”，那么事情就会很好。

有什么问题？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

当您需要/需要阅读整行时，您正在阅读下一个String。改变这个：

in.next();

通过

in.nextLine();

在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);
}

来自评论：

当我将in.next更改为in.nextLine时，同时运行程序Enter Title和Enter Author`;相反，首先输入标题应出现，并在给出标题输入作者后出现

请注意nextLine将消耗每个输入，直到Scanner找到新的断行输入。这意味着您必须在阅读图书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

Java应用程序崩溃了

1 个答案: