Question

我正在使用文件处理在java中创建一个数据库项目。该程序正在运行而不编译错误。以下几点无效

文件仅存储第一条记录。（如果程序再次运行则覆盖文件）
我想显示所有记录，但唯一的第一条记录显示为Exeception

请提供建议..

import java.io.*;

public class Student implements Serializable
{
    private int roll;                       
    private String name;                    //To store name of Student
    private int[] marks = new int[5];       //To store marks in 5 Subjects
    private double percentage;              //To store percentage
    private char grade;                     //To store grade
    public Student()
    {
        roll = 0;
        name = "";
        for(int i = 0 ; i < 5 ; i++)
            marks[i] = 0;
        percentage = 0;
        grade = ' ';
    }
    public Student(int roll , String name ,int[] marks)
    {
        setData(roll,name,marks);
    }
    public void setData(int roll , String name ,int[] marks)
    {
        this.roll = roll;
        this.name = name;
        for(int i = 0 ; i < 5 ; i++)
            this.marks[i] = marks[i];
        cal();
    }
    //Function to calculate Percentage and Grade
    private void cal()
    {
        int sum = 0;
        for(int i = 0 ; i < 5 ;i++)
            sum = sum + marks[i];
        percentage = sum/5;

        if(percentage>85)
            grade = 'A';
        else if(percentage > 70)
            grade = 'B';
        else if (percentage >55)
            grade = 'C';
        else if (percentage > 33)
            grade = 'E';
        else
            grade = 'F';
    }
    public char getGrade() { return grade; }
    public double getPercentage() { return percentage; }
    @Override
    public String toString()
    {
        string format = "Roll Number : %4d, Name : -%15s "
                      + "Percentage : %4.1f Grade : %3s";
        return String.format(format, roll, name, percentage, grade);
    }
}

第二档

import java.io.*;

public class FileOperation
{
    public static void writeRecord(ObjectOutputStream  outFile, Student temp) 
        throws IOException, ClassNotFoundException
    {
        outFile.writeObject(temp);
        outFile.flush();
    }

    public static void showAllRecords(ObjectInputStream inFile) 
        throws IOException, ClassNotFoundException
    {
        Student temp = new Student();
        while(inFile.readObject() != null)
        {
            temp = (Student)inFile.readObject();
            System.out.println(temp);
        }
    }
}

主文件（只有两个选项正在运作）

import java.util.*;
import java.io.*;

public class Project
{
    static public void main(String[] args)
        throws IOException,ClassNotFoundException
    {
        ObjectInputStream  inFile;
        ObjectOutputStream outFile;

        outFile = new ObjectOutputStream(new FileOutputStream("info.dat"));
        inFile = new ObjectInputStream(new FileInputStream("info.dat"));

        Scanner var = new Scanner(System.in) ;
        int roll;
        String name;
        int[] marks = new int[5];
        int chc = 0;

        Student s = new Student();

        while(chc != 6)
        {
            System.out.print("\t\tMENU\n\n");
            System.out.print("1.Add New Record\n");
            System.out.print("2.View All Records\n");
            System.out.print("3.Search a Record (via Roll Number) \n");
            System.out.print("4.Delete a Record (via Roll Number) \n");
            System.out.print("5.Search a Record (via Record Number)\n");
            System.out.print("6.Exit\n");
            System.out.print("Enter your choice : ");
            chc = var.nextInt();

            switch(chc)
            {
            case 1: 
                System.out.print("\nEnter Roll number of Student : ");
                roll = var.nextInt();
                System.out.print("\nEnter Name of Student : ");
                name = var.next();
                System.out.println("\nEnter marks in 5 subjects \n");
                for(int i = 0 ; i < 5 ; i++)
                {
                    System.out.print("Enter marks in subject " + (i+1) + " ");
                    marks[i] = var.nextInt();
                }
                s.setData(roll , name , marks );
                System.out.println("\n Adding Record to file \n");
                System.out.printf("Record \n " + s);
                System.out.println("\n\n");
                FileOperation.writeRecord(outFile,s);
                System.out.println("Record Added to File\n ");
                break;

            case 2:
                System.out.println("All records in File \n");
                FileOperation.showAllRecords(inFile);
                break;

            default: System.out.println("Wrong choice ");
            }
        }
        outFile.close();
        inFile.close();
    }
}

Answer 1

您的程序找到了ClassNotFoundException，您的方法只会抛出IOException。

我会检查你的import语句，以确保你引入了ObjectInputStream类

import java.io.ObjectInputStream;

如果你想摆脱未报告的异常，请尝试：

尝试

public static void showAllRecords(ObjectInputStream inFile) throws IOException, ClassNotFoundException

文件处理程序中的文件结束错误

1 个答案: