java.util.IllegalFormatPrecisionException : null(in. java.util.Formatter$FormatSpecifier

Question

我的代码可以编译，但 System.out.printf(%8d, %.1f...etc) 中出现运行时错误；

这是我的代码:

import java.io.*;
import java.util.Scanner;
public class StudentGPA
{
    public static void main(String[] args)
    throws FileNotFoundException
    {
        Scanner in = new Scanner(new File("data2.txt"));
        int studentNum,classNum,ctr;
        double avg,hours,grade,gradePts,hrsTot,gradePtsTot,GPA;        
        System.out.println("Fall 2013  Project 2  Due 9/19/13  by Tanner Triggs");
        System.out.println("STUDENT    CLASS      HOURS       GRADE       GRADE POINTS\r");

        hrsTot = 0;
        gradePtsTot = 0;
        ctr = 0;
        studentNum=in.nextInt();
        classNum=in.nextInt();
        hours=in.nextDouble();
        grade=in.nextDouble();

        while(studentNum!= -999)
        {  ctr++;
            gradePts = hours * grade;
            hrsTot+=hours;
            gradePtsTot+=gradePts;            
            System.out.printf("%8d       %.1d      %.1f       %5.2f         %.1f \r\n\n",studentNum,classNum,hours,grade,gradePts);
            studentNum=in.nextInt();
            classNum=in.nextInt();
            hours=in.nextDouble();
            grade=in.nextDouble();
            gradePts=in.nextDouble();
            GPA=1.0 * gradePtsTot / hrsTot;            
            System.out.printf("Totals:     %5.1f           %5.2f\r\n",hrsTot,gradePtsTot);           
            System.out.printf("\nSemester GPA: %.2f",GPA);


        }
    }
}

我相信我所有的“f”和“d”都是正确的，所以我认为可能是别的东西

这是数据2:

87126534   1151   5.0    3.0
87126534   5100   3.0    2.0
87126534   4101   4.0    4.0
87126534   13198  2.0    2.0
87126534   2100   3.0    4.0
-999       0      0      0

Answer 1

删除 %.1d 中的点，因为 %d 格式化程序用于整数值(整数、长整型等)。所以你的格式化程序就是 %1d。