多个字符之间有空格的字符输入

Question

我正在尝试创建一个决定一个人进入大学的机会的年级。用户应输入如下内容：A B C D F E。程序应在 E 处停止，因为它不是等级。该程序还计算 GPA。在驱动程序（包含在下面）中，我调用了 print 和 set 函数，但是它根本不退出 set 循环。

主要成绩类：

import java.util.*;
public class Grades {
//Declare instance variables here
private int numClass;
private double gpa;
public int count = 0;
public boolean gotF = false;
/**
 * Method to get the grades and calculate the GPA
 * This method also counts the number of classes taken
 * and the number of Fs
 */
public void getGradesAndCalculateGPA()
{
    //Your code goes here

    Scanner stdin = new Scanner(System.in);
    System.out.println("Enter a set of grades:");
    do {
        count += 1;
        if(stdin.next().charAt(0) == 'A') {
            gpa += 4.0;
            //System.out.println("Grade Inputted");
        }
        else if(stdin.next().charAt(0) == 'B') {
            gpa += 3.0;
            //System.out.println("Grade Inputted");
        }
        else if(stdin.next().charAt(0) == 'C') {
            gpa += 2.0;
            //System.out.println("Grade Inputted");
        }
        else if(stdin.next().charAt(0) == 'D') {
            gpa += 1.0;
            //System.out.println("Grade Inputted");
        }
        else if(stdin.next().charAt(0) == 'F') {
            gpa += 0.0;
            gotF = true;
            //System.out.println("Grade Inputted");
        }
    }while(stdin.next().charAt(0) == 'A' ||
            stdin.next().charAt(0) == 'B' ||
            stdin.next().charAt(0) == 'C' ||
            stdin.next().charAt(0) == 'D' ||
            stdin.next().charAt(0) == 'F');
    gpa = gpa/count;


}
/**
 * Method to print the appropriate message
 */
public void printMessage()
{
    //Your code goes here
    if(count < 4) {
        System.out.printf("%7s %12d %30s", "", gpa, "Ineligible, taking less than four classes");
    }
    else if(gotF==true && gpa<2.0) {
        System.out.printf("%7s %12d %30s", "", gpa, "Ineligible, gpa below 2.0 and has F grade");
    }
    else if(gotF == true) {
        System.out.printf("%7s %12d %30s", "", gpa, "Ineligible, gpa above 2.0 but has F grade");
    }
    else if(gpa < 2.0) {
        System.out.printf("%7s %12d %30s", "", gpa, "Ineligible, gpa below 2.0");
    }
    else {
        System.out.printf("%7s %12d %8s", "", gpa, "Eligible");
    }

}

}

这里是驱动类：

public class Driver {
    public static void main(String[] args) {
        Grades grader = new Grades();
        grader.getGradesAndCalculateGPA();
        grader.printMessage();
    }
}

Answer 1

每次调用 stdin.next() 时，Scanner 都会等待用户输入内容并按回车键。您的代码将这些语句与每个 if 语句叠加在一起，并扰乱了编程流程。我将您的代码修复为每个年级只要求用户输入一次，并将其存储在 grade 变量中以在 if 语句中使用。我还添加了 validGrade 布尔值以在输入无效成绩时中断循环。

Scanner stdin = new Scanner(System.in);
System.out.println("Enter a set of grades:");
boolean validGrade = true;

while (validGrade) {
    count += 1;
    char grade = stdin.next().charAt(0);
    if (grade == 'A') {
        gpa += 4.0;
        System.out.println("Grade Inputted");
    } else if (grade == 'B') {
        gpa += 3.0;
        System.out.println("Grade Inputted");
    } else if (grade == 'C') {
        gpa += 2.0;
        System.out.println("Grade Inputted");
    } else if (grade == 'D') {
        gpa += 1.0;
        System.out.println("Grade Inputted");
    } else if (grade == 'F') {
        gotF = true;
        System.out.println("Grade Inputted");
    } else {
        validGrade = false;
    }
}

gpa = gpa / count;
System.out.println("Your GPA is: " + gpa);