如何根據“studentId”從文本文件中刪除一行？

Question

我真的很有興趣有一個方法可以根據id number從文本文件中刪除一行，但我不知道如何實現這一點。

students.txt文件如下所示：

1111111,John Smith<br/> 
7777777,Dave Smith

以下是我到目前為止的代碼： 公共班學生：

public class Student  {
    // instance variables
    private int studentId;
    private String name;

    /**
     * Constructor for objects of class Student
     */
    public Student(int id, String name) {
        this.name = name;
        studentId = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String newName) {
        name = newName;
    }

    public void setId(int newId) {
        studentId = newId;
    }

    public int getId() {
        return studentId;
    }
}

公共類EnrollmentController：

public class EnrollmentController {
    private Student theStudent;
    private BufferedWriter writer;
    private BufferedReader reader;
    private final File studentFile = new File("students.txt");
    private ArrayList students = new ArrayList();

    public EnrollmentController() {
        readFromStudentFile();

    }

    public ArrayList getStudents() {
        return students;
    }

    public void addStudent(int id, String name) {
        students.add(new Student(id, name));
    }

    public void printClassList(String courseId) {

    }

    public void writeToStudentFile(int id, String name) {
        try {
            writer = new BufferedWriter(new FileWriter(studentFile, true));
            writer.write(id + "," + name + "\n");
            writer.flush();
            writer.close();
        } catch (IOException e) {
            System.out.println(e);
        }
    }

    public void readFromStudentFile() {
        students = new ArrayList();

        try {
            reader = new BufferedReader(new FileReader(studentFile));

            String line = reader.readLine();

            while (line != null) {
                String[] record = line.split(",");
                int id = Integer.parseInt(record[0]);
                Student s = new Student(id, record[1]);
                students.add(s);
                line = reader.readLine();
            }

            reader.close();
        } catch (IOException e) {
            System.out.println(e);
        }
    }

    public Student findStudent(int id) {
        boolean found = false;
        Iterator it = students.iterator();
        while (it.hasNext() && !found) {
            Student s = (Student) it.next();
            if (s.getId() == id) {
                found = true;
                return s;
            }
        }
        return null;
    }

    {
        boolean found = false;
        {
            {
                found = true;
            }
        }
    }
}

Answer 1

您可以從原始文件中讀取，僅將那些與指定ID不匹配的記錄寫入臨時文件，然后在最后用新臨時文件替換原始文件。

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.Writer;
public class Demo{
  public static void main(String[] argv)
                        throws Exception{
    Writer output = new BufferedWriter(new FileWriter("fixed.txt"));
    BufferedReader freader =
     new BufferedReader(new FileReader("orinal.txt"));
    String s;
    while ((s=freader.readLine())!=null){
      String tokens[] = s.split(",");
      String id = f[0];
      String name = f[1];
      // check against the ID or ID's you don't want. If the current ID is not the one
      // you don't want then write it to the output file
      if (!id.equals("00001") {
          output.write(s + "\n");
      }
    }
    freader.close();
    output.close();
  }
}

Answer 2

您可以使用String的split方法。 拆分","然后檢查索引0以查找您要刪除的ID。 （即在這種情況下不打印任何內容。）我將提供示例代碼，但我不再安裝Java編譯器。

Answer 3

大概你想讀所有的學生，但不是根據ID寫一個特定的學生。 因此，在這種情況下，請修改writeToStudentFile（）方法，使其類似於以下內容：

public void writeToStudentFile(int idToIgnore)
{
    try{
        writer = new BufferedWriter(new FileWriter(studentFile, true));
        Iterator it = students.iterator();
        while (it.hasNext())
        {
            Student s = (Student)it.next();
            if (s.getId() != idToIgnore)
            {
                writer.write(s.getId() + "," + s.getName() + "\n");
            }
        }
        writer.flush();
        writer.close();
    }
    catch(IOException e){System.out.println(e);}
}