Java Files
Java Files
The File class from the java.io package, allows
us to work with files.
To use the File class, create an object of
the class, and specify the filename or directory name:
Example
import java.io.File;
// Import the File class
File myObj = new
File("filename.txt"); // Specify the filename
The File class has many useful methods for creating and getting information
about files.
For example:
| Method | Type | Description |
|---|---|---|
canRead() |
Boolean | Tests whether the file is readable or not |
canWrite() |
Boolean | Tests whether the file is writable or not |
createNewFile() |
Boolean | Creates an empty file |
delete() |
Boolean | Deletes a file |
exists() |
Boolean | Tests whether the file exists |
getName() |
String | Returns the name of the file |
getAbsolutePath() |
String | Returns the absolute pathname of the file |
length() |
Long | Returns the size of the file in bytes |
list() |
String[] | Returns an array of the files in the directory |
mkdir() |
Boolean | Creates a directory |
If you don't know what a package is, read our Java Packages Tutorial.
Create a File
Use the createNewFile() method to create a file. This method returns a
boolean value: true if the file was successfully created, and false if the file
already exists. Note that the method is enclosed in a try...catch
block. This is necessary because it throws an IOException if an error occurs (if the
file cannot be created for some reason):
Example
import java.io.File; // Import the File class
import java.io.IOException; // Import the IOException class to handle
errors
public class CreateFile {
public static
void main(String[] args) {
try {
File myObj = new File("filename.txt");
if
(myObj.createNewFile()) {
System.out.println("File created: " + myObj.getName());
} else {
System.out.println("File already exists.");
}
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}
The output will be:
File created: filename.txt
To create a file in a specific directory (requires permission), specify the path of the file and use double backslashes to escape the "\" character (for Windows). On Mac and Linux you can just write the path, like: /Users/name/filename.txt
Get File Information
Now that we have created a file, we can use other File methods to get information about that file:
Example
import java.io.File;
public class GetFileInfo {
public static
void main(String[] args) {
File myObj = new
File("filename.txt");
if (myObj.exists()) {
System.out.println("File name: " + myObj.getName());
System.out.println("Absolute path: " + myObj.getAbsolutePath());
System.out.println("Writeable: " + myObj.canWrite());
System.out.println("Readable " + myObj.canRead());
System.out.println("File size in bytes " + myObj.length());
} else {
System.out.println("The file does
not exist.");
}
}
}
The output will be:
File name: filename.txt
Absolute path: C:\Users\MyName\filename.txt
Writeable: true
Readable: true
File size in bytes: 0
Write To a File
In the
following example, we use the FileWriter class together with its write() method
to write some text to the file we created in the example above. Note that when you are done writing to the file,
you should close it
with the close() method:
Example
import java.io.FileWriter; // Import the FileWriter class
import java.io.IOException; // Import the IOException class to handle
errors
public class WriteToFile {
public static void
main(String[] args) {
try {
FileWriter myWriter = new FileWriter("filename.txt");
myWriter.write("Files in Java might be tricky, but it is fun enough!");
myWriter.close();
System.out.println("Successfully wrote to the file.");
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}
The output will be:
Successfully wrote to the file.
Read a File
In the
following example, we use the Scanner class to read the contents of the text file we created in the example above:
Example
import java.io.File;
// Import the File class
import java.io.FileNotFoundException; // Import
this class to handle errors
import
java.util.Scanner; // Import the Scanner class to read text files
public class
ReadFile {
public static
void main(String[] args) {
try {
File myObj = new
File("filename.txt");
Scanner myReader =
new Scanner(myObj);
while
(myReader.hasNextLine()) {
String data = myReader.nextLine();
System.out.println(data);
}
myReader.close();
} catch (FileNotFoundException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}
The output will be:
Files in Java might be tricky, but it is fun enough!
Note: There are many available classes in the Java API that can be used to read and write files in Java: FileReader, BufferedReader, Files, Scanner, FileInputStream, FileWriter, BufferedWriter, FileOutputStream, etc. Which one to use depends on the Java version you're working with and whether you need to read bytes or characters, and the size of the file/lines etc.
