【发布时间】：2016-11-08 03:25:59
【问题描述】：
我在从学生数据库问题中读取二进制值时遇到了很多麻烦。经过一些修补后，我得到了输出以正常工作并以我想要的格式，即（int id，String name，int age）但是，我在从我的文件中加载编码的二进制数据值时遇到了很多麻烦。根据编译器，它一直读取到 UTF 值，然后我收到 EOFException。
这是我试图解决的问题：
首先，启动程序后，用户选择以下任一选项 1. 将学生添加到数据库 2. 从数据库中删除一个学生 3.打印数据库中的特定学生 4. 打印数据库中的所有学生
如果他们选择，用户会将 Student obj 添加到学生向量中。 学生 obj 包含一个 ID(int)、一个 Name(String) 和一个 age(int)。
移除一个学生会根据用户输入的 ID 号从向量中移除他们。
选项 3/4 将学生 obj(s) 打印到屏幕上（而不是二进制文件）
用户输入5退出程序后；向量中的学生 obj 被写入二进制文件。
当程序重新运行时，它会将学生 obj 重新加载到向量中。 （记住文件是从二进制文件写入和加载的）
我遇到的问题是，当我尝试加载文件“Student.data”（我当前正在写入的文件）时它一直在第 198 行向我抛出 EOFException读学生的名字。
我认为问题可能出在我编写代码时，但我修改了获取名称值并多次写入它们的方式，但仍然无法正确加载它们。
关于如何解决此问题的任何建议？
代码：
//StudentDB.java
import java.util.Vector;
import java.io.*;
import java.util.Scanner;
class Student
{
private int id;
private String name;
private int age;
//Desc: Initializes the student to id=0, name="none", and age=0
public Student()
{
this.id=0;
this.name="none";
this.age=0;
}
//Desc: Initializes the student to id=i, name=n, age=a
public Student(int I, String n, int a)
{
this.id=I;
this.name=n;
this.age=a;
}
//Desc: Sets the current id to s
public void setID(int s)
{
this.id=s;
}
//Return: The current ID value
public int getID()
{
return this.id;
}
//Desc: sets the current name of the student to s
public void setName(String s)
{
this.name=s;
}
//Return: The current name of the student
public String getName()
{
return this.name;
}
//Desc: sets the current age of the obj to a
public void setAge(int a)
{
this.age=a;
}
//Return: The students current age
public int getAge()
{
return this.age;
}
//Return: True if id of this student equals id of obj, false otherwise
public boolean equals(Object obj)
{
Student stu= (Student)obj;
if(this.id==stu.id) return true;
else return false;
}
//Desc: Compares two students based on their ID to determine if they're
// the same
//Return: 1 if the current Student's ID is greater than stu
// 0 if the students ID's are the same
// -1 if Student stu's ID is larger
public int compareTo(Student stu)
{
if(this.id> stu.id) return 1;
else if(this.id==stu.id) return 0;
else return -1;
}
//Return: id+"Name"+age
public String toString()
{
return (this.getID()+ " "+this.getName()+" "+this.getAge());
}
}
public class StudentDB
{
private static Scanner keyboard=new Scanner(System.in);
//Desc: Maintains a database of Student Records. The database is stored in
// a binary file called "Student.data"
//Input: User enters commands from keyboard to manipulate database
//Output: Database updated as directed by user.
public static void main(String[]args) throws IOException
{
Vector<Student> v= new Vector<Student>();
File s= new File("Student.data");
if(s.exists()) loadStudent(v);
int choice=5;
do
{
System.out.println("\t1. Add a Student Record");
System.out.println("\t2. Remove a Student Record");
System.out.println("\t3. Print a Student Record");
System.out.println("\t4. Print all Student Records");
System.out.println("\t5. Quit");
choice= keyboard.nextInt();
keyboard.nextLine();
switch(choice)
{
case 1: addStudent(v); break;
case 2: removeStudent(v); break;
case 3: printStudent(v); break;
case 4: printAllStudent(v); break;
default: break;
}
} while(choice!=5);
storeStudent(v);
}
//Input: user enters an integer(id), a string(name), an integer(age) from
//the keyboard all on seperate lines
//Post: The input record added to v if id does not exist
//Output: various prompts as well as "Student Added" or "Add failed:
// Student already exists" printed on the screen accordingly
public static void addStudent(Vector<Student> v)
{
Student stu= new Student();
System.out.print("Please enter a Student ID:");
stu.setID(keyboard.nextInt());
keyboard.nextLine();
System.out.print("Please enter a Student Name:");
stu.setName(keyboard.nextLine());
System.out.print("Please enter a Student Age:");
stu.setAge(keyboard.nextInt());
keyboard.nextLine();
int index= v.indexOf(stu);
if(index==-1)
{
v.add(stu);
System.out.println("Student Added");
}
else System.out.println("Add failed: Student already exists");
}
//Input: user enters an integer(id) from the Keyboard
//Post: The records in v whose id field matches the input removed from v
//Output: various prompts as well as "Student removed" or "Remove failed:
// Student does not exsist" printed on the screen accordingly
public static void removeStudent(Vector<Student>v)
{
System.out.print("Student ID:");
int id= keyboard.nextInt();
Student stu= new Student(id,"",99);
if(v.remove(stu)) System.out.println("Student Removed");
else System.out.println("Remove Failed");
}
//Input: user enters an integer(id) from the Keyboard
//Output: various prompts as well as the record in v whose id field
// matches the input printed on the screen or "Print failed: Student
// does not exsist" printed on the screen accordingly
public static void printStudent(Vector<Student>v)
{
System.out.print("Student ID:");
int id= keyboard.nextInt();
Student stu= new Student(id,"",99);
int index=v.indexOf(stu);
if(index!=-1)
{
System.out.println(v.get(index).toString());
}
else System.out.println("Print failed: Student does not exsist!");
}
//Output: All records in v printed on the screen
public static void printAllStudent(Vector<Student>v)
{
Student stu=new Student();
for(int i=0; i<v.size();++i)
{
stu=v.get(i);
System.out.println(stu);
}
}
//Input: Binary file Student.data must exist and contains student records
//Post: All records in Student.data loaded into vector v.
public static void loadStudent(Vector<Student>v)throws IOException
{
Student stu;
int c;
DataInputStream f= new DataInputStream(
new FileInputStream("Student.data"));
try {
while(true)
{
stu=new Student();
int id=f.readInt();
stu.setID(id);
String name= f.readUTF();
stu.setName(name);
int age= f.readInt();
stu.setAge(age);
v.add(stu);
}
}
catch(EOFException e)
{
System.out.println("Error!: End of File Exception");
f.close();
}
catch(IOException e)
{
System.out.println("Error Reading File");
f.close();
System.exit(1);
}
f.close();
}
//Output: All records in v written to binary file Student.data
public static void storeStudent(Vector<Student>v) throws IOException
{
Student stu= new Student();
DataOutputStream s= new DataOutputStream(
new FileOutputStream("Student.data"));
for(int i=0; i<v.size(); ++i)
{
stu=v.get(i);
s.writeInt(stu.getID());
s.writeUTF(stu.getName());
s.writeInt(stu.getAge());
}
s.close();
}
}
【问题讨论】：
-
编辑您的姓名和电子邮件，哈哈。还提供示例用法。遇到错误的
main方法。 -
因为文件里有随机的垃圾字符，看一下十六进制编辑器自己看看。您不必删除学生即可导致错误。您所要做的就是添加一个学生。意味着你的写操作很糟糕。
标签： java database utf-8 binary binaryfiles