File I/O - Java - page 562

Notice that almost all the code in the sample program in Display 10.13 is in a try
block. Any part of the code that does binary file I/O in the ways we are describing can
throw an IOException .
The output stream for writing to the binary file numbers.dat is created and named
with the following:

ObjectOutputStream outputStream =
new ObjectOutputStream( new FileOutputStream("numbers.dat"));

As with text files, this is called opening the file . If the file numbers.dat does not
already exist, this statement will create an empty file named numbers.dat . If the file
numbers.dat already exists, this statement will erase the contents of the file so that the
file starts out empty. The situation is basically the same as what you learned for text
files, except that we're using a different class.
As is typical of Java I/O classes, the constructor for the class ObjectOutputStream
takes another I/O class object as an argument, in this case an anonymous argument of
the class FileOutputStream .

opening a file

Opening a Binary File for Output
You create a stream of the class ObjectOutputStream and connect it to a binary file as
follows:
SYNTAX
ObjectOutputStream Output_Stream_Name =
new ObjectOutputStream( new FileOutputStream( File_Name ));

The constructor for FileOutputStream may throw a FileNotFoundException , which is
a kind of IOException . If the FileOutputStream constructor succeeds, then the con-
structor for ObjectOutputStream may throw a different IOException . A single catch
block for IOException would cover all cases.
EXAMPLES
ObjectOutputStream myOutputStream =
new ObjectOutputStream( new FileOutputStream("mydata.dat"));

After opening the file, you can use the methods of the class ObjectOutputStream (Display
10.14) to write to the file.

The class ObjectOutputStream does not have a method named println , as we had with
text file output and screen output. However, as shown in Display 10.13, an object of the
class ObjectOutputStream does have a method named writeInt that can write a single int
value to a file, and it also has the other output methods described in Display 10.14.
In Display 10.13, we made it look as though the numbers in the file numbers.dat
were written one per line in a human-readable form. That is not what happens, however.
There are no lines or other separators between the numbers. Instead, the numbers are

writeInt