Java Input and Output

Question

Explain the difference between the outputs of the following two fragments of code for outputting an int i to a file:

i)

PrintWriter outfile = new PrintWriter(new FileWriter("ints.txt"));
outfile.print(i);

ii)

DataOutputStream out = new DataOutputStream(new FileOutputStream("ints.dat"));
out.writeInt(i);

I think the Printer writer takes a string and tranforms it into a stream of unicode characters, whereas dataoutput stream converts the data items to sequence of bytes.

What more would you add?

Sounds like homework. If it is so, please tag it accordingly. — Howard
– Howard, Commented Apr 22, 2011 at 12:52

Peter Lawrey · Accepted Answer · 2011-04-22 12:52:51Z

1

Files only contain byte, so it all ends up as bytes in the end.

A String is already a stream of characters. When you write a String to a file it has to turn it into a stream of bytes.

An int is four bytes. writeInt() turns it into a big endian number.

answered Apr 22, 2011 at 12:52

Peter Lawrey

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MarcoS · Accepted Answer · 2011-04-22 13:01:53Z

1

From DataOutputStream javadoc:

A data output stream lets an application write primitive Java data types to an output stream in a portable way. An application can then use a data input stream to read the data back in.

From PrintWriter javadoc

Prints formatted representations of objects to a text-output stream.

Everything is just bytes, but they represent different things. With a DataOutpuStream you get bytes that you can read back directly to your primitive Java type int, whereas with a PrintWriter you don't.

answered Apr 22, 2011 at 13:01

MarcoS

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Liv · Accepted Answer · 2011-04-22 13:05:57Z

0

possibly repeating what was already said, but just to make it more explicit:

when you use a printwriter, and say you have an int value of 65 -- the print writer will print 2 characters: '6' and '5'

when you use an outputstream, this prints bytes so it will write to the file a byte with the value of 65 -- this happens to be the character code in ASCII/UTF-8 for 'A' so if you open up the file in a text editor you will see an "A" character -- rather than '6' followed by '5' as above.

answered Apr 22, 2011 at 13:05

Liv

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