數組列表中的掃描程序錯誤

Question

我正在創建一個程序，它將文件名作爲參數並在文本中檢查迴文。該程序還將根據用戶輸入替換字母或根據用戶輸入刪除單詞。出於某種原因，掃描儀在

public void letter 

and 

public void word 

無法正常工作。

這是我在程序運行和用戶類型後收到錯誤：

What would you like to do? Here are your options: 

Press 1 to Print all palindromes 

Press 2 to Replace any letter 

Press 3 to remove all occurences of a word 

Press 4 to exit 

2 

What letter would you like to remove? 

e 

What letter would you like to add? 

r 

[ ] 

What would you like to do? Here are your options: 

Press 1 to Print all palindromes 

Press 2 to Replace any letter 

Press 3 to remove all occurences of a word 

Press 4 to exit 

這是錯誤，我得到

Exception in thread "main" java.util.NoSuchElementException 
at java.util.Scanner.throwFor(Scanner.java:907) 
at java.util.Scanner.next(Scanner.java:1416) 
at Homework6.main(Homework6.java:28)** 

代碼：

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

public class Test { 

static ArrayList<String> strings = new ArrayList<String>(); 

public static void main(String[] args) { 
    Test test2 = new Test(); 
    try { 
     Scanner scanner = new Scanner(new File(args[0])); 
     while (scanner.hasNext()) { 
      strings.add(scanner.next()); 
     } 
    } catch (Exception e) { 
    } 

      //ArrayList<String> a = new ArrayList<String>(strings); 
    while (true) { 
     System.out.println("\nWhat would you like to do? Here are your options: \nPress 1 to Print all palindromes \nPress 2 to Replace any letter \nPress 3 to remove all occurences of a word \nPress 4 to exit\n"); 
     Scanner s = new Scanner(System.in); 
     String command = s.next(); 

     if (command.equals("1")) { 
      test2.pal(); 
     } else if (command.equals("2")) { 
      test2.letter(); 
     } else if (command.equals("3")) { 
      test2.word(); 
     } else if (command.equals("4")) { 
      System.exit(0); 
     } 
    } 
} 

public void pal() { 
    int a; 
    int c; 
    // boolean isPalindrome() ; 

    for (a = 0; a < strings.size(); a++) { 
     String replace = strings.get(a); 
     replace = replace.replaceAll("[.,']", ""); 
    } 

    for (c = 0; c < strings.size(); c++) { 
     boolean pal = PalindromeChecker.isPalindrome(strings.get(c)); 

     if (true) { 
      System.out.print(strings.get(c)); 
     } 
    } 
} 

public void letter() { 

    int b; 
    Scanner replaceLetter = new Scanner(System.in); 
    System.out.println("What letter would you like to remove?"); 
    String badLetter = replaceLetter.next(); 
    System.out.println("What letter would you like to add?"); 
    String newLetter = replaceLetter.next(); 
    for (b = 0; b < strings.size(); b++) { 
     String replaceVowels = strings.get(b); 
     replaceVowels = replaceVowels.replace("badVowel", "newVowel"); 
    } 
    replaceLetter.close(); 

    System.out.print(strings); 
} 

public void word() { 

    Scanner removeWord = new Scanner(System.in); 
    System.out.println("What word would you like to remove?"); 
    String word = removeWord.next(); 
    strings.remove(word); 
    removeWord.close(); 
    System.out.print(strings); 
} 
} 

Answer 1

刪除這些行..它會工作...

 replaceLetter.close(); 
    removeWord.close(); 

Answer 2

使用

while(scanner.hasNextLine()){} 

和scanner.nextLine

，而不是hasNext() & next()。

如果你正在使用java7那麼這將是最好的，以這樣的代碼：

try (Scanner scanner = new Scanner(new FileInputStream(file)) { 

} 

它會自動關閉Scanner並且是安全的任何類型的leak

Answer 3

擴大對@ TheLostMind的回答，問題是當你撥打Scanner#close時，如果它實現了Closeable接口，它也會關閉底層流。從文檔摘自：

如果掃描儀尚未如果它的底層 readable也實現Closeable接口，則可讀的 close方法將被調用關閉即可。如果此掃描儀已關閉，則調用此方法的 將不起作用。

因此，在您的letter()和word()功能，當你調用close，它也將關閉System.in。因此，當您嘗試使用Scanner再次從System.in中讀取時，沒有什麼可以閱讀的，並且您得到了NoSuchElementException。