Javaの外部ファイルからテキストを印刷する

Question

そのファイルに1行のテキストを含む外部ファイルを作成し、その行をJavaプログラムで印刷しようとしています。私が試してみました;しかし、私は問題を抱えています。私のコードはエラーを投げているわけではなく、正しく動作していません。

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

public class App { 

public static void main(String[] args) { 

    String terminate = "X"; 
    String Question = ""; 
    System.out.println("I am the all-knowing Magic 8 Ball!"); 

    do { 
     Scanner scnr = new Scanner(System.in); 
     System.out.println(""); 
     System.out.println("Ask your question here or enter 'X' to exit:"); 
     Question = scnr.nextLine(); 
     continueGame(Question); 
    } while (terminate != Question); 


     String testData[] = {"test1", "test2", "test3"}; 
     writeFile(testData, "data.txt"); 
     ArrayList<String> fileContents = readFile("data.txt"); 

     if (terminate.equalsIgnoreCase(Question)) { 
     for (String contents : fileContents) { 
      System.out.println(contents); 
     }   
    } 
    } 

public static void continueGame(String Question) { 

    char terminate = 'X'; 
    char condition = Question.charAt(0); 

    if (condition == terminate) 
    { 
     System.out.println(""); 
     System.out.println("Thanks for playing!"); 
     System.exit(0); 
    } 
    try 
    { 
     Random rand = new Random(); 
     int choice; 
     choice = 1 + rand.nextInt(20); 
     responseOptions(choice, Question); 
    } 
    catch (Exception e) 
    { 
     System.out.println("Error: Invalid"); 
    } 
} 

public static void responseOptions(int choice, String answer) 
{ 
    switch (choice) 
    { 
     case 1: answer = "Response: It is certain"; break; 
     case 2: answer = "Response: It is decidely so"; break; 
     case 3: answer = "Response: Without a doubt"; break; 
     case 4: answer = "Response: Yes, definitely"; break; 
     case 5: answer = "Response: You may rely on it"; break; 
     case 6: answer = "Response: As I see it, yes"; break; 
     case 7: answer = "Response: Most likely"; break; 
     case 8: answer = "Response: Outlook good"; break; 
     case 9: answer = "Response: Yes"; break; 
     case 10: answer = "Response: Signs point to yes"; break; 
     case 11: answer = "Response: Reply hazy, try again"; break; 
     case 12: answer = "Response: Ask again later"; break; 
     case 13: answer = "Response: Better not tell you now"; break; 
     case 14: answer = "Response: Cannot predict now"; break; 
     case 15: answer = "Response: Concentrate and ask again"; break; 
     case 16: answer = "Response: Don't count on it"; break; 
     case 17: answer = "Response: My reply is no"; break; 
     case 18: answer = "Response: My sources say no"; break; 
     case 19: answer = "Response: Outlook not so good"; break; 
     case 20: answer = "Response: Very doubtful"; break; 
    } 
    System.out.println(""); 
    System.out.println(answer); 
} 

public static void writeFile(String arrayToWrite[], String filename) { 

    try { 
     PrintWriter wordWriter = new PrintWriter("filename.txt"); 
     for (String words : arrayToWrite) { 
      wordWriter.println(words + "\n"); 
     } 
    } catch (Exception e) { 
     String msg = e.getMessage(); 
     System.out.print(msg); 
    } 
} 

public static ArrayList<String> readFile(String filename) { 
    ArrayList<String> fileContents = new ArrayList(); 
    File myFile = new File(filename); 

    try { 
     Scanner scnr = new Scanner(myFile); 
     String tempStr = ""; 
     while (scnr.hasNextLine()) { 
      tempStr = scnr.nextLine(); 
      fileContents.add(tempStr); 
     } 
    } catch (Exception e) { 
     String msg = e.getMessage(); 
     System.out.println(msg); 
    } 
    return fileContents; 
} 
} 

Answer 1

あなたのコードの問題は、あなたがwriteFile()でfilenameを得ているが、あなたはfilenameとして有するファイル名をしていないが、代わりにあなたがfilename.txtでファイルを作っているということです。 readFile()の中にはまだ作成されていないファイルfilenameがありますが、new file(filename)はファイルが存在しないため空のファイルを作成します。そして、あなたは空のファイルを読んでいます。彼らはあなたに問題が発生しますエラーを通じてないよう余分なノートで、あなたのwriteFile()内のコードの下に

try{ 
    FileWriter fw=new FileWriter(filename); 
    for (String words : arrayToWrite) { 
     fw.write(words + "\n"); 
    } 
    fw.close(); 

    }catch(Exception e){ 
    System.out.println(e); 
} 

を入れてはPrintWriterまたはPrintStreamWriterを使用しないようにしてください。