java - 尝试编写一个使用 OutputStream 写入文本文件的循环

Question

我不是java程序员，我是VB程序员。我这样做是作为作业的一部分，但是，我并没有在与作业相关的事情上寻求帮助。我想弄清楚如何让 OutputStreamWriter 在这种情况下正常工作。我只想捕获我生成的值并将它们放入文本文档中。该文件已生成，但只存在一个条目，而不是我期望的 40 个条目。我可以用 VB 在心跳中做到这一点，但现在 java 对我来说感觉很陌生。感谢您的帮助。

谢谢，

史蒂夫

代码如下:

  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

您正在循环中关闭文件。下一次在循环中您将尝试写入已关闭的文件，这将引发异常...但是在您捕获 IOException 的地方您有一个空 block ，这将有效地忽略异常。

尝试将 out.close() 调用移动到 finally block 中，如下所示:

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