为什么我的代码没有创建新文件？

Question

这是我刚写的一门课。以前它实际上在另一个应用程序中创建了一个文件。但不知何故，它不起作用。它没有创建新文件，我收到此错误：

package hostelmanagement;

/**
 *
 * @author princess
 */
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

import java.io.Externalizable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JOptionPane;

/**
 *
 * @author princess
 */
public class Student implements Serializable, Externalizable  {

public static Set<Student> listOfStudents = new HashSet<Student>();    
public static File oFile = new File("Student.dat"); 


//Data Members
private String studentID;
private String name;
private Date dateOfReg;

//Constructor 
Student(String number,String name)
{
this.studentID = number;
this.name = name;
dateOfReg = new Date(); 
}


public String getName()
{
return name;
}

public String getStudentID()
{
return studentID;
}

public Date getDateOfReg()
{
return dateOfReg;
}

public void register() throws FileNotFoundException, IOException, ClassNotFoundException    
{    

HashSet<Student> sss = Student.getListOfStudents();
sss.add(this);
FileOutputStream OFileStream = new FileOutputStream(oFile);    
ObjectOutputStream ObjectOFileStream = new ObjectOutputStream(OFileStream);    
ObjectOFileStream.writeObject(sss);
ObjectOFileStream.close();      
}

public static HashSet<Student> getListOfStudents() throws FileNotFoundException, IOException, ClassNotFoundException
{
HashSet ss;
File iFile = new File("Student.dat");
FileInputStream IFileStream = new FileInputStream(iFile);
 ObjectInputStream ObjectIFileStream = new ObjectInputStream(IFileStream);
ss = (HashSet<Student>) ObjectIFileStream.readObject();
ObjectIFileStream.close();
return  (HashSet<Student>) ss;
}

public static void printListOfStudents() throws FileNotFoundException, IOException, ClassNotFoundException
{
HashSet<Student> sa = Student.getListOfStudents();
for (Student x : sa)
{System.out.println(x.toString());}
}


public static Student getStudentByID(String aNumber) throws FileNotFoundException, IOException, ClassNotFoundException
{ 
HashSet<Student> currentListOfStudents = Student.getListOfStudents();    
Student result = null;   
for (Student x : currentListOfStudents) 
    {   
if (x.getStudentID().equalsIgnoreCase(aNumber))  
        { result = x;
             break;
        }
    }  
      if (result == null)
    {
        JOptionPane.showMessageDialog(null, "Student not found");
    }
    return result; 
}



    @Override
public String toString()
{
// include the code to retrieve assigned apartment    
return "Name: " + name +" StudentID: "+ studentID + " Registered On: " + dateOfReg;
}


    @Override
public boolean equals(Object another)
{
Student stud = (Student)another;
return this.name.equals(stud.name)&& this.studentID.equals(stud.studentID);
}

    @Override
public int hashCode()
{
int hash = name.hashCode();
return hash;

}

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

错误：

run:
Test 1
Apr 27, 2012 10:19:30 AM hostelmanagement.HostelManagement main
SEVERE: null
java.io.FileNotFoundException: Student.dat (The system cannot find the file specified)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:106)
    at hostelmanagement.Student.getListOfStudents(Student.java:86)
    at hostelmanagement.Student.register(Student.java:74)
    at hostelmanagement.HostelManagement.main(HostelManagement.java:34)
Exception in thread "main" java.io.FileNotFoundException: Student.dat (The system cannot find the file specified)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:106)
    at hostelmanagement.Student.getListOfStudents(Student.java:86)
    at hostelmanagement.HostelManagement.main(HostelManagement.java:46)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

问题出在哪里？

Answer 1

鉴于您没有提供主要逻辑，我假设您在调用register()（写入文件）之前先调用getListStudents()（读取文件）。它没有找到它并不奇怪。

问题是您的程序试图读取一个仍然不存在的文件，而不是它未能创建它。请仔细阅读您的堆栈跟踪。

Answer 2

您的错误表明您正在尝试读取不存在的文件。它只会在您尝试写入时创建新文件。

我会做以下事情。

public static Set<Student> getListOfStudents() throws IOException, ClassNotFoundException {
    File studentFile = new File("Student.dat");
    FileInputStream in = null;
    try {
        in = new FileInputStream(studentFile);
        ObjectInputStream oos = new ObjectInputStream(in);
        retyurn (Set<Student>) oos.readObject();
    } catch(FileNotFoundException noStudents) {
        return new HashSet<Student>();
    } finally {
        if (in != null)
           try {
               in.close();
           } catch(IOException ignored) {}
    }
}

Answer 3

问题可能是您在getListOfStudents() 和register() 方法中加载的文件可能不在指定位置。