加载/读取 .txt 文件

Question

我在 Java 入门课程中的最后一个作业要求我们：

1. 编写一个基于控制台（AKA 基于命令行）的菜单供您的用户进行交互。
2. 在菜单中包含以下命令（您必须为每个命令编写代码）：
   1. 输入学生列表，使用 ArrayDemo 中的菜单：显示、添加、删除等。
   2. 使用用户提供的文件名将学生列表保存到文件中
   3. 使用用户提供的文件名从文件中加载学生列表。

我已经做了1-3。如何让我的程序将信息加载到 .txt 文件中？ （老实说，我不确定这是否是我的老师说加载时的意思，因为我觉得这可能比我们讨论的要复杂一些）

我已经能够让我的程序使用记事本打开 .txt 文件，但我不知道如何让它读取整个文件和/或将文本信息保存到我的程序中。

import java.util.*;
import java.util.Scanner;
import java.io.*;

public class ArrayDemo_File {
    private static Student[]   StudentList = new Student[10];
    private static FileWriter  file;
    private static PrintWriter output;
    private static FileReader fr;

    public static void StudentIndex() {
        int index = 0;

        while (index < StudentList.length) {
            if(StudentList[index] != null) {
                System.out.println(index + ": " + StudentList[index].getLName() + ", " 
                    + StudentList[index].getFName());
            }
            else {
                return;
            }

            index++;
        }
    }

    // View detailed data for Students listed in the index
    public static void IndexData() {
        int index = 0;

        while (index < StudentList.length) {
            if(StudentList[index] !=null) {
                System.out.println(index + ": " + StudentList[index].getLName() + ", " + StudentList[index].getFName());
                System.out.println("A Number: \t" + StudentList[index].getANum());
                System.out.println("Address: \t" + StudentList[index].getAddress());
                System.out.println();
            }
            else {
                return;
            }

            index++;
        }
    }

    // ADD STUDENT
    public static void AddStudent() throws IOException {
        // Memory
        Student student = new Student();
        Address address = new Address();
        Scanner kb = new Scanner(System.in);

        String last;
        String frst;
        int num;

        int house;
        String Street;
        String City;
        String State;
        int Zip;
        String Line2;

        // Student Name and ID
        System.out.println();
        System.out.print("Last Name:\t");
        last = kb.nextLine();

        System.out.println();
        System.out.print("First Name:\t");
        frst = kb.nextLine();

        System.out.println();
        System.out.print("A Number:\tA");
        num = kb.nextInt();

        //Address
        System.out.println();
        System.out.print("What is your house number?\t");
        house = kb.nextInt(); 
        kb.nextLine();

        System.out.println();
        System.out.print("What is your Street's name?\t");
        Street = kb.nextLine();

        System.out.println();
        System.out.print("What is your city?\t");
        City = kb.nextLine();

        System.out.println();
        System.out.print("What is your State?\t");
        State = kb.nextLine();

        System.out.println();
        System.out.print("What is your zip code?\t");
        Zip = kb.nextInt();

        kb.nextLine();

        System.out.println();
        System.out.print("Line 2: \t");
        Line2 = kb.nextLine();

        System.out.println("");

        // Processing
        address = new Address( house, Street, City, State, Zip, Line2 );
        student = new Student(last, frst, num, address);

        int index = 0;

        while( index < StudentList.length ) {
            if( StudentList[index] == null ) break;
            index++;
        }

        StudentList[index] = student;
    }

    // REMOVE STUDENT
    public static void RemoveStudent() {
        System.out.println("Remove student");

        int index = 0;

        while (index < StudentList.length) {
            if (StudentList[index] !=null) {
                System.out.println(index + ": " + StudentList[index].getLName() + " " +     StudentList[index].getFName());
            }
            index++;
        }

        Scanner kb = new Scanner(System.in);
        int response;

        System.out.println(" Please enter student number to remove or -1 to cancel removal");
        System.out.print("\nInput: ");

        response = Integer.parseInt(kb.nextLine());

        if (response != -1) {
            StudentList[response] = null;
        }

        Student[] StudentListTemp = new Student[10];
        int nulls = 0;
        for(int x = 0; x < StudentList.length; x++) {
            if (StudentList[x] == null) {
                nulls++;
            }
            else {
                StudentListTemp[x - nulls] = StudentList[x];
            }
        }

        StudentList = StudentListTemp;
    }


    public static void WriteFile() throws IOException {
        String fileName;
        Scanner kb = new Scanner(System.in);

        System.out.println("Please enter a  name for your file: ");
        fileName = kb.nextLine();

        output = new PrintWriter(fileName + ".txt");

        for( int x = 0; x < StudentList.length; x++ ) {
            if( StudentList[x] == null )
                continue;

            output.println( "[" + x + "]" );
            output.println( StudentList[x].getFName()   );
            output.println( StudentList[x].getLName()   );
            output.println( StudentList[x].getAddress() );
        }

        output.close();

        System.out.println("\n\tFile saved successfully!");
    }

    public static void loadFile() throws IOException {
        Student student = new Student();
        String fileName;
        Scanner kb = new Scanner(System.in);

        System.out.println("Please enter the name of the file: ");
        fileName = kb.nextLine();

        File file = new File(fileName + ".txt");
        if(!file.exists()) {
            System.err.println("\n\tError(404)): File Not Found!");
        }
        else {
            System.out.println("\n\tFile found! It will now open!");

            //FileReader fr = new FileReader(fileName + ".txt");
            //System.out.println(fr);
            ProcessBuilder pb = new ProcessBuilder("Notepad.exe", fileName + ".txt");
            pb.start();
        }
    }

    //CONSOLE MENU
    public static void Menu() throws IOException {
        Scanner kb = new Scanner(System.in);
        int response;
        boolean run = true;

        while(run) {
            System.out.println("--------------------------" );
            System.out.println("  OPTIONS:                 ");
            System.out.println(" 0) View Student Names     ");
            System.out.println(" 1) View Student details   ");
            System.out.println(" 2) Add Student            ");
            System.out.println(" 3) Remove Student         ");
            System.out.println(" 4) Save to File           ");
            System.out.println(" 5) Load File              ");
            System.out.println(" 6) Close Program          ");
            System.out.println("-------------------------- ");
            System.out.print(" Choose an option: ");

            response = Integer.parseInt(kb.nextLine());

            System.out.println();

            switch(response) {
                case 0:
                    StudentIndex();
                    break;
                case 1:
                    IndexData();
                    break;
                case 2:
                    AddStudent();
                    break;
                case 3:
                    RemoveStudent();
                    break;
                case 4:
                    WriteFile();
                    break;
                case 5:
                    loadFile();
                    break;
                case 6:
                    run = false;
                    break;
                default:
                    System.out.println(" ERROR: "+ response + " ! ");
            }
        }

        System.out.println( "Have a nice day!" );
    }

    public static void main(String[] args) throws IOException {
        // StudentList[0] = new Student("Doe", "Jon", 0000, new Address(00, "Road", "City", "State", 37343, "000"));
        // StudentList[1] = new Student("Ricketts", "Caleb", 0001, new Address(000, "000", "000", "0000", 000, "000"));
        // StudentList[2] = new Student("Smith", "Amanda", 2222, new Address(000, "000", "000", "000", 000, "000"));
        // StudentList[3] = new Student("Wilson", "Judy", 3333, new Address(000, "000", "000", "000", 000, "000"));

        Menu();
    }
}

我尝试使用filereader 读取文件，但它没有输出任何内容。不知道我做错了什么。

Answer 1

使用这些代码，您可以在 SDCard 中编写一个文本文件，同时您需要在 android manifest 中设置权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

在写入文件之前，还要检查您的 SDCard 是否已挂载以及您的外部存储状态是否可写

Environment.getExternalStorageState()

鳕鱼：

public void generateNoteOnSD(String sFileName, String sBody){
    try
    {
        File root = new File(Environment.getExternalStorageDirectory(), "Notes");
        if (!root.exists()) {
            root.mkdirs();
        }
        File gpxfile = new File(root, sFileName);
        FileWriter writer = new FileWriter(gpxfile);
        writer.append(sBody);
        writer.flush();
        writer.close();
        Toast.makeText(this, "Saved", Toast.LENGTH_SHORT).show();
    }
    catch(IOException e)
    {
         e.printStackTrace();
         importError = e.getMessage();
         iError();
    }
   }  

---

Check the http://developer.android.com/guide/topics/data/data-storage.html

Answer 2

扫描仪在读取 .txt 文件方面做得很好。使用另一个 Scanner 对象读取文件，一次一行。代码完成后，文件的每一行都将存储在列表中，每一行都在相应的索引处（例如：list.get(0) 将返回第一行，list.get(1) 返回第二行，等等）。

   public static void loadFile()
   {
      Student student = new Student();
      String fileName;
      Scanner kb = new Scanner(System.in);
      Scanner read;
      ArrayList<String> list = new ArrayList<String>();

      System.out.println("Please enter the name of the file: ");
      fileName = kb.nextLine();

      File file = new File(fileName + ".txt");
      if(!file.exists())
      {
         System.err.println("\n\tError(404)): File Not Found!");

      } else {
         System.out.println("\n\tFile found! It will now open!");
         read = new Scanner(file);
         //FileReader fr = new FileReader(fileName + ".txt");
         //System.out.println(fr);
         //ProcessBuilder pb = new ProcessBuilder("Notepad.exe", fileName + ".txt");
         //pb.start();
         while(read.hasNextLine()) {
            String currentLine = read.nextLine();
            list.add(currentLine);
         }
      }

   }