Question

我的程序在没有编译错误的意义上正常工作。一旦我浏览了数据并输入了一些测试数据，例如名字：Bob，姓：Jones，课程：IT，等级：44。首先，它将它存储在＆＃34; Grades.txt＆＃34;文件。但是，当我重新运行程序时，文件会重置并且它是空的。为什么是这样？就好像数据只是临时存储在文件中一样。感谢

代码：

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.PrintWriter;
import java.util.Scanner;

     public class ExamGrades {

    public static void main(String[] args) throws Exception {
        FileWriter grades = new FileWriter("grades.txt");
        BufferedWriter bw = new BufferedWriter(grades);
        PrintWriter out = new PrintWriter(bw);
        Scanner scan = new Scanner(System.in);

        int examMark =0;
        String firstName = "";
        String surName = "";
        String course = "";

            System.out.print("Please enter student firstname: ");
            firstName = scan.next();

            System.out.print("Please enter student surname: ");
            surName = scan.next();

            System.out.print("Please select student course: ");
            course = scan.next(); // Drop Down menu in future?

            System.out.print("Please enter student mark: ");
            while (!scan.hasNextInt())
            {
                System.out.print("Please enter a valid mark: ");
                scan.next();
            }
            examMark = scan.nextInt();

            if (examMark < 40)
            {
                System.out.println("Failed");
            }
            else if (examMark >= 40 && examMark <= 49)
            {
                System.out.println("3rd");
            }
            else if (examMark >= 50 && examMark <= 59)
            {
                System.out.println("2/2");
            }
            else if (examMark >= 60 && examMark <= 69)
            {
                System.out.println("2/1");
            }
            else if (examMark >= 70 && examMark <= 100)
            {
                System.out.println("1st");
            }
            else
            {
                System.out.println("Invalid Mark"); // If not within previous criteria, this prints
            }

        out.print(firstName + " ");
        out.print(surName + ", ");
        out.print(course + ", ");
        out.print(examMark);


        out.close();
        scan.close();
    }
}

Answer 1

您需要将true作为第二个参数传递给FileWriter构造函数。

FileWriter构造函数接受的第二个参数名为＆＃34; append＆＃34;并确保FileWriter附加到文件而不是覆盖它。

例如：

FileWriter grades = new FileWriter("grades.txt", true);

程序运行时文件中没有数据 - java

1 个答案: