java - 为什么使用 do while 循环时会跳过 nextLine

Question

这个问题已经存在:

Scanner issue when using nextLine after nextXXX [duplicate]

已关闭 10 年前。

我必须为我的类(class)编写一个程序，该程序接受用户输入的作业、实验、测试等，将它们放入一个字符串中，并且有一个单独的类将它们分成单独的“双”数字并包含一个 writeToFile将学生的成绩写入文件的方法。

但我一直遇到问题..当我第一次询问用户的名字时，它工作正常，但如果用户决定再次进入 do-while 循环，则会跳过“你叫什么名字”它直接转到 id。我知道这与最后一个输入不是字符串有关，解决方案是放置一个“keyboard.nextLine();”在问题上方，但我尝试过，它只是在询问问题之前询问用户的姓名..

import java.util.Scanner; 
    import java.io.*;
    import java.text.DecimalFormat;

    public class GradeApplication
    {
        public static void main(String[] args) throws IOException 
        {
            Scanner keyboard = new Scanner(System.in);

            //Define variables
            String name;
            int id;
            String homework;
            String labs;
            String tests;
            double project;
            double discussion;
          int answer;

            do
            {
                System.out.print("\nWhat is your name? ");
                name=keyboard.nextLine();

                System.out.print("\nWhat is your student ID? ");
                id=keyboard.nextInt();

                homework = keyboard.nextLine();
                System.out.println("\nPlease enter homework grades separated by spaces:");
                homework = keyboard.nextLine();

                System.out.println("Please enter lab grades separated by spaces:");
                labs = keyboard.nextLine();

                System.out.println("Please enter test grades separated by spaces:");
                tests = keyboard.nextLine();

                System.out.println("Please enter project grade:");
                project = keyboard.nextDouble();

                System.out.println("Please enter discussion grade:");
                discussion = keyboard.nextDouble();

                System.out.println("\nResults: ");
                //Call toString method
                Student_Khazma s = new Student_Khazma(name,id,homework,labs,tests,project,discussion);
                System.out.print(s.toString()); 

     //Open file         
         PrintWriter outputFile= new PrintWriter("gradeReport.txt");
         System.out.println(s.writeToFile());
         outputFile.close();

         System.out.print("\n\nWould you like to see your grade report again? (1 is yes, 2 is no): ");
         answer=keyboard.nextInt();

             System.out.print("\n\nWould you like to see your grade report again? (1 is yes, 2 is no): ");
             answer=keyboard.nextInt();

                }while(answer==1);

        }
    }

Answer 1

您最后一次调用Scanner#nextInt() :

    ...
    System.out.print("\n\nWould you like to see your grade report again? (1 is yes, 2 is no): ");
    answer=keyboard.nextInt();

} while(answer==1);

不消耗换行符，因此它会传递到您第一次调用 Scanner#nextLine()。因此，扫描操作不会阻塞等待输入(详细信息请参阅javadoc)。要解决这个问题，您需要添加keyboard.nextLine();:

    ...
    System.out.print("\n\nWould you like to see your grade report again? (1 is yes, 2 is no): ");
    answer=keyboard.nextInt();
    keyboard.nextLine(); // <== line added here
} while(answer==1);

这样您对 nextLine() 的第一次调用将阻止输入(当循环重新启动时)。