試圖編寫一個使用OutputStream寫入文本文件的循環

Question

我不是一個java程序員，我是一名VB程序員。我將此作爲一項任務的一部分，但是，我並沒有要求有關任務的幫助。在這種情況下，我想弄清楚如何讓OutputStreamWriter正常工作。我只想捕獲我生成的值並將它們放入文本文檔中。該文件生成，但只有一個條目存在，而不是我期待的40。我可以用VB來做到這一點，但是現在我覺得Java很奇怪。感謝您的幫助。

感謝，

史蒂夫

下面的代碼：

public static void main(String[] args) { 
    long start, end; 
    double result,difference; 

    try { 
     //OutputStream code assistance from 
     // http://tutorials.jenkov.com/java-io/outputstreamwriter.html 
     OutputStream outputStream = new FileOutputStream("c:\\Temp\\output1.txt"); 
     Writer out = new OutputStreamWriter(outputStream); 

     for(int n=1; n<=20; n++) { 
     //Calculate the Time for n^2. 
     start = System.nanoTime(); 

     //Add code to call method to calculate n^2 
     result = mN2(n); 
     end = System.nanoTime(); 
     difference = (end - start); 

     //Output results to a file 
     out.write("N^2 End time: " + end + " Difference: " + 
      difference + "\n"); 
     out.close(); 
     } 
    } catch (IOException e){ 
    } 

    try { 
     OutputStream outputStream = new FileOutputStream("c:\\Temp\\output1.txt"); 
     Writer out = new OutputStreamWriter(outputStream); 

     for(int n=1; n<=20; n++){ 
     //Calculate the Time for 2^n. 
     start = System.nanoTime(); 
     //Add code to call method to calculate 2^n 
     result = m2N(n); 
     end = System.nanoTime(); 
     difference = (end - start); 
     //Output results to a file 
     out.write("N^2 End time: " + end + " Difference: " + difference + "\n"); 
     out.close(); 
     } 
    } catch (IOException e){ 
    } 
    } 

    //Calculate N^2 
    public static double mN2(double n) { 
    n = n*n; 
    return n; 
    } 

    //Calculate 2N 
    public static double m2N(double n) { 
    n = 2*n; 
    return n; 
    } 

Answer 1

你在循環中關閉您的文件。下次在循環中，你將嘗試寫入封閉的文件，這將拋出一個異常......但是你在哪裏捕獲到了一個空塊，它將有效地忽略異常。

嘗試out.close()呼叫移動到finally塊，像這樣：

try { 
    ... 
} 
catch (IOExcetpion e) { 
    // Log any errors 
} 
finally { 
    out.close(); 
}