Question

我一直在＆＃34; java.lang.IllegalStateException＆＃34;在使用Scanner（）

之后

这就是我所拥有的

public void insertBook(){ //this method allows the user to insert a new book in the database

    Boolean select = false;
    Scanner input = new Scanner(System.in);

    File textFile = new File("src/newbooks.txt");
    FileWriter fw = null; //FileWriter and BufferedWriter have to be initialized and used inside a try catch
                          //to be used outside, initialize the objects as null
    BufferedWriter bw = null;
    try{
        fw = new FileWriter(textFile);//check if it can read the textfile
        bw = new BufferedWriter(fw);//FileWriter has to be wrapped in BufferedWriter
    }catch(IOException e){
        System.out.println("the file could not be found");
        }//end catch

    System.out.println(" select is " +select);//if(text == "n")

    System.out.println("enter the book information below");
    System.out.println("if the informatin is not available, enter\"information not available\"");
    System.out.print("do you wnat to enter a book? ");
    String text = input.next();

    if(text.equals("n"))
            select = true;

    do{

        String book = new String();

        if(select == true)
            break;


        if(text.equals("n")){
            System.out.print("inside if no\n");
            select = true;
            //break;//break here so 
        }
        else if (text.equals("y")){
            System.out.println("inside if y");
            try{

                Scanner input2 = new Scanner(System.in);

                System.out.print("enter the title of the book: ");
                book = input2.next();
                bw.write(book + ", ");
                System.out.println("after first write");

                System.out.print("enter the author: ");
                book = input2.next();
                bw.write(book + ", ");
                System.out.println();

                System.out.print("enter the year of the book: ");
                book = input2.next();
                bw.write(book + ", ");
                System.out.println();

                System.out.print("enter the gender: ");
                book = input2.next();
                bw.write(book + ", ");
                //System.out.println();

                System.out.print("enter a description: ");
                book = input2.next();
                bw.write(book + ", ");
                System.out.println();

                bw.write("\n");
                input2.close();
                select = false;
            }
            catch(IOException e){
                System.out.println("the text could not be read");
            }
            input.close();
        }
        else{
            System.out.println("you didn't enter a valid selection");
        }


        System.out.print("do you want to enter another booK? Enter y for yes and n for no");
        text = input.nextLine(); //error here
        if(text.equals("n"))
            select = true;

    }while(select == false);//end while select

    //input.close();
}//end of insert method

每当我尝试在if语句之外使用Scanner时，它都会遇到相同的错误。如果我输入了错误的选择或＆＃34; n＆＃34;，它会起作用，但如果我选择＆＃34; y＆＃34;并输入扫描程序到达do-while循环内输入的最后一行后失败的数据。

Answer 1

            ...

            bw.write("\n");
            input2.close();
            select = false;
        }
        catch(IOException e){
            System.out.println("the text could not be read");
        }

您在此处关闭扫描仪：

        input.close(); // <- remove this line
    }
    else{
        System.out.println("you didn't enter a valid selection");
    }

    ...

这里已经关闭了。

    ...  

    text = input.nextLine();
    if(text.equals("n"))
        select = true;

    ...

上次需要后关闭扫描仪。

这是因为您无法从关闭的扫描仪请求新行。

在有关扫描仪的API文档中了解有关它的更多信息：

public void close（）

关闭此扫描仪。如果这个扫描仪还没有   如果它的底层可读也实现了   可关闭的接口然后将调用可读的close方法。   如果此扫描仪已关闭，则调用此方法将具有   没有效果。

尝试在扫描程序后执行搜索操作   关闭将导致IllegalStateException。

http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#close()

使用扫描仪时为什么会出现IllegalStateException？

1 个答案: