Java Reference
In-Depth Information
Display 10.10
Redirecting Error Messages
(part 2 of 2)
21 System.setErr(errStream);
22 System.err.println("Hello from System.err.");
23 System.out.println("Hello from System.out.");
24 System.err.println("Hello again from System.err.");
None of
System.in
,
System.out
, or
System.err
needs to be closed, but the
streams you create should be explicitly
closed.
25 errStream.close();
26 }
27 }
F
ILE
errormessages.txt
Hello from System.err.
Hello again from System.err.
Screen Output
Hello from System.out.
10.3
The
File
Class
The scars of others should teach us caution.
SAINT JEROME
In this section, we describe the class
File
, which is not really an I/O stream class but
is often used in conjunction with file I/O. The class
File
is so important to file I/O
programming that it was even placed in the
java.io
package.
Programming with the
File
Class
The
File
class contains methods that allow you to check various properties of a file,
such as whether there is a file with a specified name, whether the file can be written to,
and so forth. Display 10.11 gives a sample program that uses the class
File
with text
files. (The class
File
works the same with binary files as it does with text files.)
Note that the
File
class constructor takes a name, known as the
abstract name
, as
an (string) argument. So the
File
class really checks properties of names. For example,
the method
exists
tests whether there is a file with the abstract name. Moreover, the
abstract name may be a potential directory (folder) name. For example, the method
isDirectory
tests whether the abstract name is the name of a directory (folder). The
abstract name may be either a relative path name (which includes the case of a simple
file name) or a full path name.
Display 10.12 lists some of the methods in the class
File
.
abstract name
