Java Reference
In-Depth Information
characters, but we can't count on such things. Instead, we should specify a file name by using Java's path
specifiers, as shown in listing 8-2.
Second, notice that we must handle an exception to work with a File object. Nearly all the methods
in the various Input/Output classes and interfaces throw an
IOException
. As we learned when we
covered the basics of exceptions in Chapter 2, “Java Syntax,” Java objects generally throw exceptions
whenever something beyond the bounds of your program might cause a problem. In the case of
methods that deal with files, your program cannot anticipate all the things that can go wrong on the file
system. You might inadvertently specify a directory or drive that does not exist or specify an invalid file
name. For example, my laptop has no Z drive. So, if I try to create
Z:\\test\\myFile.txt
, the program
fails. Listing 8-2 shows how to create a file with a path that works on any operating system (so long as a
JVM exists for that operating system).
Listing 8-2. Creating an empty file with path specifiers
package com.apress.java7forabsolutebeginners.examples;
import java.io.File;
public class FileTest {
public static void main(String[] args) {
String fileName = "C:" + File.separator +
"test" + File.separator + "myFile.txt";
File myFile = new File(fileName);
try {
myFile.createNewFile();
} catch (Exception e) {
System.out.println("Couldn't create " + myFile.getPath());
}
System.out.println("Created " + myFile.getPath());
}
}
Now, no matter what system we run the program on, we get a proper path for our file. If everything
else works (the C drive exists, the
test
directory exists, our program has permission to write a file in that
location, and so on), we get a new and empty text file where we expect it.
Opening a File
You probably can't get by with just writing new files all the time, so you should know how to open a file
that already exists, too. What opening a file really amounts to is creating a
File
object that corresponds
to a file on the file system. Then, through that
File
object, you can do various things to the contents of
the file. We get to manipulating contents later; for now, let's just get a
File
object for an existing file.
Because we already created
myFile.txt
, let's get a File object for that file. To make sure we actually
found a file, we use the
exists()
method to check for a file, as shown in see Listing 8-3.
