<identifier> Java中预期的编译错误[3]

Question

import java.io.*;

class attendance_and_student_management {
    BufferedReader bw = new BufferedReader(new InputStreamReader(System.in));

    File f5 = new File("e.txt");
    f5.createNewFile();
    File f4 = new File("d.txt");
    f4.createNewFile();
    File f3 = new File("c.txt");
    f3.createNewFile();
    File f2 = new File("b.txt");
    f2.createNewFile();
    File f1 = new File("a.txt");
    f1.createNewFile();
}

I am trying to create 5 files at the beginning of my program, however when I compile my program the compiler highlights f5.createNewFile (); and give the error expected.

Answer 1

You need to wrap your code in a method. You can't have normal statements directly inside a class.

A good method for you to wrap this in is in a main method:

import java.io.*;

class attendance_and_student_management {
    public static void main(String[] args) {
        BufferedReader bw = new BufferedReader(new InputStreamReader(System.in));

        File f5 = new File("e.txt");
        f5.createNewFile();
        File f4 = new File("d.txt");
        f4.createNewFile();
        File f3 = new File("c.txt");
        f3.createNewFile();
        File f2 = new File("b.txt");
        f2.createNewFile();
        File f1 = new File("a.txt");
        f1.createNewFile();
    }
}

By putting it in a main method, you can directly invoke this class from the command line with java -cp <classpath> attendance_and_student_management .

Note that by Java naming conventions, class names should use CamelCase and start with a capital. So the proper name for your class per these conventions is AttendanceAndStudentManagement .

Answer 2

You can have "normal statements" in a class as static initialization like this:

public class AttendanceAndStudentManagement {
  BufferedReader bw = new BufferedReader(new InputStreamReader(System.in));

  static {
    try {
      File f5 = new File("e.txt");
      f5.createNewFile();
      File f4 = new File("d.txt");
      f4.createNewFile();
      File f3 = new File("c.txt");
      f3.createNewFile();
      File f2 = new File("b.txt");
      f2.createNewFile();
      File f1 = new File("a.txt");
      f1.createNewFile();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

Depending on your use case, this may be preferable to adding a main() method because it also works in presence of a main() method in another class. The static blocks are executed when the class is loaded, ie before the first object is instantiated or the first call to a static method.