爲什麼當它試圖從文件讀取時出現錯誤？

Question

我正在編寫一個程序，可以使用傳統的加密方法對消息進行編碼和解碼。該消息將從文件讀入並寫入輸出文件。下面的程序是用java編寫的，並且沒有錯誤編譯。當我運行程序來測試它是否在我給它輸入和輸出文件的名稱後運行時，它會運行成某種異常拋出錯誤。我認爲問題在於代碼中的for循環。這是一個將所有消息存儲到字符數組中的循環。任何建議，以解決它或另一個更好的工作的數據結構（如堆棧或隊列）？

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

class CryptoProject1 
{ 
static char eord; 
static Scanner cin=new Scanner(System.in); 
static char [] message=new char[10000]; 

public static void main (String [] args) 
    throws IOException 
{ 
    //getting the input txt file name from user 
    String infilename; 
    System.out.println("Please give the name of the input file."); 
    infilename=cin.nextLine(); 
    Scanner fileread=new Scanner (new FileReader(infilename)); 

    //getting the output txt file name from user 
    String outfilename; 
    System.out.println("Please give the name of the output file."); 
    outfilename=cin.nextLine(); 
    PrintWriter filewrite=new PrintWriter(new FileWriter(outfilename)); 

    //saving the message into an array 
    //construct/make it into a usable function?? 
    for(int i=0; i<message.length; i++) 
    { 
     message[i]=fileread.next().charAt(0); 
    } 

    //trial to make sure it reads and writes correctly 
    //printing the message onto the output file 
    for(int i=0; i<message.length; i++) 
    { 
     filewrite.print(message[i]); 
    } 

} 

Answer 1

for(int i=0; i<message.length; i++) 
{ 
    message[i]=fileread.next().charAt(0); 
} 

在這裏，你可以不知道，如果文件長度大於消息相同或更高，文件也可以具有10個字符。你需要這樣做：

for(int i=0; i<message.length; i++) 
{ 
    if(!fileread.hasNext()) 
    break; 
    message[i]=fileread.next().charAt(0); 
} 

只是一個簡單的檢查，如果還有東西要從文件中讀取，如果沒有，然後停止閱讀。

另外，習慣上使用Java對象File來表示文件，而不是使用字符串來保存文件路徑。例如：

private File output; 
public void create file(String path) 
{ 
    output = new File(path); 
} 

private BufferedWriter out = new BufferedWriter(new FileWriter(output)); 

Answer 2

此外，當您寫入一個文件，請確保您調用close（）方法關閉它或它的內容將不會被保存

Answer 3

//I ran this code without an error 
//getting the input txt file name from user 
String infilename; 
System.out.println("Please give the name of the input file."); 
infilename=cin.nextLine(); 
Scanner fileread=new Scanner (new FileReader(infilename)); 

//getting the output txt file name from user 
String outfilename; 
System.out.println("Please give the name of the output file."); 
outfilename=cin.nextLine(); 
PrintWriter filewrite=new PrintWriter(new FileWriter(outfilename)); 

//saving the message into an array 
//construct/make it into a usable function?? 
for(int i=0; i<message.length; i++) 
{ 
    if(fileread.hasNext()) 
    message[i]=fileread.next().charAt(0); 
} 
fileread.close(); 

//trial to make sure it reads and writes correctly 
//printing the message onto the output file 
for(int i=0; i<message.length; i++) 
{ 
    filewrite.print(message[i]); 
} 
filewrite.close(); 
}