閱讀文本文件中的字符串

Question

比方說，我在我的文本文件，這樣的文字：

VOTED/1/hannah/18 
NOT VOTING/2/janice/20 

，我有這樣的代碼：

File Orig_outFile = new File("C:\\voters.txt"); 
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile)); 

vNum=JOptionPane.showInputDialog("Enter voters number: "); 
String line=""; 
String something="VOTED"; 
while(infile.readLine()!=null){ 
    line=infile.readLine(); 
    String [] info=line.split("/"); 

    if(info[1].matches(vNum)){ 
    while(info[0].matches(something)){ 
     JOptionPane.showMessageDialog(null, "Voter already voted or Voter not registered. Please try again"); 
     vNum=JOptionPane.showInputDialog("Enter voters number: "); 
    } 
    President(); 
    } 
} 
infile.close(); 

任務是需要用戶輸入選民號碼，然後閱讀文本文件，然後如果發現文本文件中的info[0]包含VOTED，它將收到錯誤消息並需要再次輸入其選民號碼。我假設我的錯誤是我使用while循環兩次？

Answer 1

其實你正在做infile.readLine()並通過再次做infile.readLine()追加下一行字符串line讀一本線while。

你最終只會讀取文件中的第二行。你應該改變你的while循環，如下所示：

while((line = infile.readLine()) != null) 

，並刪除下面的語句：

line = infile.readLine(); 

以下是更正後的代碼片段：

File Orig_outFile = new File("C:\\voters.txt"); 
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile)); 

vNum = JOptionPane.showInputDialog("Enter voters number: "); 
String line = null; 
String something = "VOTED"; 
while((line = infile.readLine()) != null) { 
    String [] info = line.split("/"); 

    /* Assuming You Are Entering Voter's Number & Not Voter's Name */ 
    if(info[1].equalsIgnoreCase(vNum)) { 
     if(info[0].equalsIgnoreCase(something)) { 
      JOptionPane.showMessageDialog(null, "Voter already voted or 
              Voter not registered. Please try again"); 
      /* Please Note That You Are Currently Iterating File */ 
      /* If You Do This Here, You'll End Up Checking Same Records */ 
      /* You'll Have To Replace Outer `if` with `while` */ 
      vNum = JOptionPane.showInputDialog("Enter voters number: "); 
     } else { 
      President(); 
      break; 
     } 
    } 
} 
infile.close(); 

這裏有一個更清晰的方法實施它：

1. 讀取存儲器中的完整文件（最好用Map鍵 - >選通號碼）。

2. 取用戶的選民號碼，並檢查它是否存在於地圖中。

3. 如果它在Map中不存在或者值等於VOTED則重複Step 2。

這裏是代碼片段：

File Orig_outFile = new File("C:\\voters.txt"); 
BufferedReader infile = new BufferedReader(new FileReader(Orig_outFile)); 
Map<String,String> map = new HashMap<>(); 
String something = "VOTED"; 

String line = null; 
while((line = infile.readLine()) != null) { 
    String [] info = line.split("/"); 
    map.add(info[1],info[0]); 
} 
infile.close(); 

while(true) { 
    vNum = JOptionPane.showInputDialog("Enter Voter's Number: "); 
    if(map.contains(info[1]) && !map.get(info[1]).equalsIgnoreCase(something)) { 
     President(); 
     break; 
    } else { 
     JOptionPane.showMessageDialog(null, "Voter already voted or 
              Voter not registered. Please try again"); 
    } 
} 

Answer 2

調用infile.readLine()實際上從文件中讀取一行，返回並移動到下一行。要調用它兩次，一次在while循環條件：

line = infile.readLine(); 

你應該只把它曾經在while循環的條件和分配：

while(infile.readLine() != null) 

在循環的第一線

並再次值爲line變量，如下所示：

while((line = infile.readLine()) != null)