即使满足条件，while循环也不会终止-Java

Question

我不确定出了什么问题，我的教授也很困惑。只有当条件立即满足时，while 循环条件才会终止。一旦循环运行，满足条件不再停止它，它只会继续运行。看起来好像不再检查状况了？下面是我的代码。感谢您的帮助。

    import java.io.*;
    import java.util.*;


public class createPhoneList {

    public static void main(String[] args) {

        DataOutputStream ostream;//creates output stream
        Scanner input = new Scanner(System.in);//creates scanner in object
        final String DONE = "DONE";//will be used to end data entry loop
        String firstName;
        String lastName;
        long phoneNumber;

        try{
            ostream = new DataOutputStream(new   FileOutputStream("javaContactsUnit4Assignment.txt"));
            System.out.print("Enter First Name or type 'DONE' to quit: ");
            firstName = input.nextLine();
            while(!firstName.equalsIgnoreCase(DONE)){
                /*
                 * Error occuring at runtime where while loop terminates only if
                 * "done" is typed first, but once the loop is running "done" no longer
                 * stops it. Not sure what is wrong...
                 */
                input.nextLine();
                System.out.print("Please enter Last Name: ");
                lastName = input.nextLine();
                System.out.print("Please enter the Phone Number(with NO DASHES, as they will cause a fatal error): ");
                phoneNumber = input.nextLong();
                ostream.writeUTF(firstName);
                ostream.writeUTF(lastName);
                ostream.writeLong(phoneNumber);

                System.out.print("Enter First Name or type 'DONE' to quit: ");
                firstName = input.nextLine();
                }

        }
        catch(IOException e){
            System.err.println("Error opening file.");
        }
        catch(InputMismatchException e){
            System.err.println("Invalid data was entered. Please try again.");
        }
        catch(Exception e){
            System.err.println("You encountered a fatal error. Please try again.");
        }

    }
}

Answer 1

您应该在phoneNumber = input.nextLong(); 之后添加另一个input.nextLine();。

这是因为input.nextLong() 命令只读取长值（并跳过\n，这是您紧随其后按下的回车键）。

因此，当您继续使用input.nextLine() 阅读时，您会收到\n 而不是"done"，这就是您的循环永远不会终止的原因。因此，添加另一个input.nextLine() 将“吞下”\n，而下一个将读取实际的字符串。