In Java, does closing a parent input stream close its child, too?

Question

FileInputStream fis = new FileInputStream(gzipFile);
GZIPInputStream gis = new GZIPInputStream(fis);
gis.close();
fis.close();

Is fis.close() necessary? Though I'm running this code and don't seem to get any errors.

Answer 1

You should see the implementation of GZIPInputStream.close().

/**
 * Closes this input stream and releases any system resources associated
 * with the stream.
 * @exception IOException if an I/O error has occurred
 */
public void close() throws IOException {
    if (!closed) {
        super.close();  
        eos = true;
        closed = true;
    }
}

If you take a look at the constructor for GZIPInputStream, it looks like this:

/**
 * Creates a new input stream with the specified buffer size.
 * @param in the input stream
 * @param size the input buffer size
 * @exception IOException if an I/O error has occurred
 * @exception IllegalArgumentException if size is <= 0
 */
public GZIPInputStream(InputStream in, int size) throws IOException {
super(in, new Inflater(true), size);
    usesDefaultInflater = true;
        readHeader(in);
}

Watch the variable in. Notice how it is being passed to the super class which is InflaterInputStream in this case.

Now, if we have a look at the implementation of InflaterInputStream.close() method, we will find this:

/**
 * Closes this input stream and releases any system resources associated
 * with the stream.
 * @exception IOException if an I/O error has occurred
 */
public void close() throws IOException {
    if (!closed) {
        if (usesDefaultInflater)
            inf.end();
    in.close();
        closed = true;
    }
}

Clearly, in.close() is being called. So the wrapped (decorated) FileInputStream is also closed on the call to GZIPInputStream.close(). Thich makes calling fis.close() redundant.