程序兩次詢問相同的響應？

Question

My Student Records 程序要求用戶在 do while 循環中輸入一次學生的名字。 用戶可以選擇通過輸入 yes 再次輸入相同的數據，並且相同的問題“輸入學生的名字：”出現兩次，一個在另一個之上。

我在那個 while 循環中插入了斷點，一旦用戶在 do 結束時選擇“是”，它就會上升到第一個 while 循環中的第一行，然后是第二行、第三行，然后又回到第一行，然后是第二個，第三個，然后進入下一個 while 循環，詢問學生的姓氏。

為什么我的程序在 do while 循環的第二次將第一個問題吐兩次？

package assignment_3;

import java.util.Scanner;

/**
 * @author Diego
 */
public class Demo {

    public static void main (String args[]) {

    //Instantiating new recordsObject
        StudentRecords recordsObject = new StudentRecords();
        String firstName = "";
        String lastName = "";
        String idNumber = "";
        String major = "";         

        Scanner keyboard = new Scanner(System.in);   

        //Asking the user to enter the students' info

        do {

            while ( firstName.isEmpty() ) {
                System.out.println("Enter student's first name: ");
                firstName = keyboard.nextLine();   
            }

           while ( lastName.isEmpty() ) {
                System.out.println("Enter student's last name: ");   
                lastName = keyboard.nextLine();
            }

            while ( idNumber.length() != 9 ) {
                System.out.println("Enter student's nine-digit ID#: ");
                idNumber = keyboard.nextLine();
            }

            while ( major.isEmpty() ) {
                System.out.println("Enter student's major: ");
                major = keyboard.nextLine();
            }

            //Concatinating first name and last name into name
            String name = firstName + " " + lastName;

            //Adding the new entry to the StudentArrayList
            StudentEntry entry = new StudentEntry (name ,idNumber, major);
            recordsObject.addStudentEntry (entry);

            //Resetting variables
            firstName = "";
            lastName = "";
            idNumber = "";
            major = "";

           /*If the user enters "yes" then they can submit more.
            If they enter "no", then all submitted info will be shown */
            System.out.println("Type yes to add another entry");
        } while (keyboard.next().equalsIgnoreCase("YES"));
        keyboard.close();

        //Printing out those entries

        System.out.println("Student Records");
        System.out.println("---------------");
        for (int index = 0 ; index < recordsObject.StudentArrayList.size() ; index++) {
            System.out.println(recordsObject.StudentArrayList.get(index));
            System.out.println("");
        }
    }
}

Answer 1

該問題是由在主 while 循環中使用 keyboard.next() 引起的。 Next 不讀取換行符。 因此，當用戶鍵入“yes”時，讀取下一個 firstName 的代碼將自動讀取剩余的換行符，仍然將 firstName 保留為空。 而且，由於 firstName 仍然為空，它會再次提示。

改變：

} while (keyboard.next().equalsIgnoreCase("YES"));

至：

} while (keyboard.nextLine().equalsIgnoreCase("YES"));