File I/O - Absolute Java - page 617

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 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
constructor 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 written in the file one immediately after the other, and they are encoded
as a sequence of bytes in the same way that the numbers would be encoded in the
computer's main memory. These coded int values cannot be read using your editor.
Realistically, they can be read only by another Java program.
You can use a stream from the class ObjectOutputStream to output values of any
primitive type and also to write data of the type String . Each primitive data type has
a corresponding write method in the class ObjectOutputStream . We have already
mentioned the write methods for outputting int values. The methods for the other
primitive types are completely analogous to writeInt . For example, the following
would write a double value, a boolean value, and a char value to the binary file
connected to the ObjectOutputStream object outputStream :

writeInt

outputStream.writeDouble(9.99);
outputStream.writeBoolean( false );
outputStream.writeChar(( int )'A');