变量未在不同情况下初始化

Question

//（old）你好，所以我正在编写一个程序，要求用户提供一个选项并运行为每个方法创建的方法 有2个输入文件“ input1.txt”和“ input2.txt”，但我不会在这里包含它们，因为它们占用了太多空间，这与问题无关。因此，到目前为止，我只完成了选项2的工作，但是当我在hackerank上对其进行测试时，有些不对劲。

（new）以下是我的代码（未完成代码）

更新：您好，下面我会发布完整的修订代码，

import static java.lang.System.*;
import java.io.FileNotFoundException;
import java.util.*;
import java.io.*;
import java.math.*;
import java.text.*;
import java.util.ArrayList;

public class Main
{
  public static void main (String[]args) throws IOException
  {
    PrintWriter pw1 = new PrintWriter ("input.txt");
      pw1.println ("Mickey Mouse CS 98.7 67.8 23.5");
      pw1.println ("Minnie Mouse ENG 45.6 98.3 94.7");
      pw1.println ("Donald Duck NET 56.8 74.2 78.4");
      pw1.println ("Bob Builder CS 78.5 89.4 82.5");
      pw1.println ("Snow White MAT 56.6 32.4 56.6");
      pw1.println ("Hellen Keller CHEM 78.8 23.1 99.6");
      pw1.println ("Daffy Duck ENG 67.4 55.5 89.5");
      pw1.println ("Fred Flinstone MAT 45.3 87.4 38.9");
      pw1.println ("Daffy Duck CS 76.5 22.2 88.5");
      pw1.println ("Bugs Bunny NET 68.4 89.7 95.6");
      pw1.println ("Winnie Pooh CHEM 77.5 89.4 98.2");
      pw1.close ();
    PrintWriter pw2 = new PrintWriter ("input2.txt");
      pw2.println ("Scrooge McDuck ACC 78.7 77.3 63.5");
      pw2.println ("Woody Woodbecker CS 65.6 78.3 84.7");
      pw2.println ("Scooby Doo MAT 56.8 78.2 88.4");
      pw2.println ("Spider Man CHEM 58.5 99.3 92.5");
      pw2.println ("Roger rabbit NET 66.9 39.6 86.6");
      pw2.println ("Wonder Woman CHEM 68.4 83.1 69.6");
      pw2.println ("Jane Jetson ENG 77.4 85.5 69.5");
      pw2.close ();


      options ();
    Scanner k = new Scanner (System.in);
    int choice = k.nextInt ();
k.nextLine();


    /*while (choice==1){

       ArrayList<student> student=uploadStudents("input.txt");
       //System.out.println(student);//[student@49e4cb85, student@2133c8f8, .....
       //bunch of reference?
       System.out.println("***Data uploaded successfully.\n");              
       options();

       choice=k.nextInt();

       }

       while (choice==2){

       printStudentData(in);    

       options();

       choice=k.nextInt();   
       } */

    while (choice != 6)
      {
    File in;
    switch (choice)
      {

      case 1:
        System.out.printf("What is the name of the file you want to upload data from?\n");
       
        String filename = k.nextLine ();
        switch (filename)
          {

          case "input.txt":
        in = new File (filename);
        java.util.ArrayList < student > student = uploadStudents (in);
        //System.out.println(student);//[student@49e4cb85, student@2133c8f8, .....
        //bunch of reference?
        System.out.println ("***Data uploaded successfully.\n");
        options ();
        choice = k.nextInt ();
                k.nextLine ();
        while(choice==2){
       
         printStudentData(in);    // if you don't ask again it will infinitely print;
         System.out.println("");
         
         options();
        
        choice=k.nextInt();
        k.nextLine();
        }
            
    break;

        case "input2.txt":
            in = new File (filename);
        java.util.ArrayList < student > student2 = uploadStudents (in);
        System.out.println ("***Data uploaded successfully.\n");
        options ();
        choice = k.nextInt ();
        k.nextLine();
        while(choice==2){
       
         printStudentData(in);    // if you don't ask again it will infinitely print;
         System.out.println("");
         
         options();
        
        choice=k.nextInt();
        k.nextLine();
        }    
        break;
          }
        break;
        
        case 2:
            out.printf ("no data found");   // if you don't ask again it will infinitely print;
          System.out.println ("");

          options ();

          choice = k.nextInt ();
                k.nextLine ();
          break;

        case 6:
            
            break;
default:
out.println("no data found");

      }
      }
  }

  public static void options ()
  {             //
    System.out.
      println
      ("Welcome to the Student Analyzer program. Please choose from the following options:");
    System.out.println ("1. Upload data");
    System.out.println ("2. View data");
    System.out.println ("3. Find Major");
    System.out.println ("4. Create statistics File");
    System.out.println ("5. Print Statistics File");
    System.out.println ("6. Exit the program");
  }             //


  public static ArrayList < student > uploadStudents (File inputfilename) throws IOException    ///
  {
    java.util.ArrayList < student > student = new java.util.ArrayList <> ();



    Scanner sc = new Scanner (inputfilename);

    while (sc.hasNext ())
      {
    //new student object??
    student s =
      new student (sc.next (), sc.next (), sc.next (), sc.nextFloat (),
               sc.nextFloat (), sc.nextFloat ());
      student.add (s);
      }



    return student;

  }             /// 

  public static void printStudentData (File inputfile) throws IOException
  {

    Scanner o = new Scanner (inputfile);
    while (o.hasNext ())
        System.out.
    printf ("Student: %s %s, Major: %s, Exam Grades: %.1f, %.1f, %.1f%n",
        o.next (), o.next (), o.next (), o.nextFloat (),
        o.nextFloat (), o.nextFloat ());
      o.close ();
  }



}

我能够通过使用Switch语句在情况下使其正常工作，但是我真的不可能修改代码并使其功能功能；我尝试初始化开关的文件，而当这样的循环'in = new file（“？”）; 但是它只需返回thread“ main” java.io.filenotfoundexception中的异常：（否此类文件或目录）

////（old），所以基本上是在我在hackerank上运行它时，它说

Student.java:104：错误：可能没有初始化的printStudentData（in）; ^ 1错误

如何重写程序，以便情况2使用案例1创建的文件？/////

Answer 1

在开始之前，您最好在中使用的默认值。之后，如果在情况1中初始化，则可以在情况2中使用它。