Exceptional Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 108

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Puzzle 41: Field and Stream
This method copies one file to another and was designed to close every stream it creates, even if it
encounters I/O errors. Unfortunately, it doesn't always do this. Why not, and how can you fix it?
static void copy(String src, String dest) throws IOException {
InputStream in = null;
OutputStream out = null;
try {
in = new FileInputStream(src);
out = new FileOutputStream(dest);
byte[] buf = new byte[1024];
int n;
while ((n = in.read(buf)) >= 0)
out.write(buf, 0, n);
} finally {
if (in != null) in.close();
if (out != null) out.close();
}
}
Solution 41: Field and Stream
This program seems to have all the bases covered. The stream fields ( in and out ) are initialized to
null and set to the new streams as soon as they are created. The finally block closes the stream
referred to by each field if it is non-null. An error during the copy would cause an IOException , but
the finally block would still execute before the method returns. What could go wrong?
The problem is in the finally block itself. The close method can throw an IOException too. If