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Thread: Dont understand objects used with FileInputStream and FileOutputStream constructor

  1. #1
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    Question Dont understand objects used with FileInputStream and FileOutputStream constructor

    In the code below, both fin and fout variables are set to null. Why is this. In the second and third "try block" fin and fout are compared to "null". Why is this? Please help me with my question.

    Thanks,
    Truck35

     // Copy a File.
        try {
          // Attempt to open the files.
          fin = new FileInputStream(args[0]);
          fout = new FileOutputStream(args[1]);
     
          do {
            i = fin.read();
            if(i != -1) fout.write(i);
          } while(i != -1);
     
        } catch(IOException exc) {
          System.out.println("I/O Error: " + exc);
        } finally {
          try {
            fin != null) fin.close();    //code in question
          } catch(IOException exc) {
            System.out.println("Error Closing Input File");
          }
          try {
             if(fout != null) fout.close();   //code in question
            } catch(IOException exc) {
            System.out.println("Error Closing Output File");
          }
        }
      }
    }


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Dont understand objects used with FileInputStream and FileOutputStream constructor

    Please post code in the form of an SSCCE- this code does not contain the lines you're talking about, so it's pretty hard to answer your question.

    My guess would be that both streams are compared to null in case there was an Exception while attempting to create them. If they weren't created, you can't close them.

    They're initially set to null so that this comparison can happen in the first place. Java doesn't assign null to variables inside functions, so you have to specifically tell it to set the variable to null. If you didn't do that, this code wouldn't work - in fact you'd probably get a compilation error.

    But like I said, without an SSCCE, I'm just guessing.
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