Food for thought : Closing I/O streams ....

Question

hi all,
my intention is to release all the I/O streams after i have finished their use .to do it i call the .Close()
method in a finally block .
my question is : how is calling .Close() on an I/O stream different from, assigning a null to it .
i.e. :
objIOStream.Close();// in finally
objIOStream = null; // in finally
will the gc behave differently in these two cases ?
what is the logical diffrence in the two approaches ?
can i be sure that my streams would be closed/resources freed by using even the second approach ?
thanks in advance,
Ravi

Answer 1

It's not quite the same thing.
Closing the stream may cause it to set its internal stream to null but that doesn't mean that the outer stream becomes available for garbage collection.
For example, in the following, outerStream doesn't gets garbage collected although it does get closed. When close is called, the FileInputStream that it wraps is closed and, according to your last post, the reference to it set to null - the FileInputStream should then be eligible for garbage collection. However, my Test class still maintains a reference to the BufferedInputStream thus preventing it from being garbage collected even though it can no longer do anything useful with it.
public class Test
  private InputStream outerStream;
  public Test() throws Exception
    try
      outerStream = new BufferedInputStream(new FileInputStream("C:/blah.txt"));
    finally
      outerStream.close();
}Explicitly setting objects to null in order to get them garbage collected is usually unnecessary, however. In the example above outerStream should have been declared locally in the constructor - it will then be eligible for garbage collection when it falls out of scope.
Hope this helps.