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File Handling in Java – How To Work With Java Files?

Published on Jul 15,2019 91 Views
A tech enthusiast in Java, Image Processing, Cloud Computing, Hadoop. A tech enthusiast in Java, Image Processing, Cloud Computing, Hadoop.
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Java being one of the most popular programming languages provides extensive support to various functionalities like database, sockets, etc. One such functionality is File Handling in Java. File Handling is necessary to perform various tasks on a file, such as read, write, etc. In this article, I will tell you what are the various file operations in Java.

Below topics are covered in this article:

What is File Handling in Java?

File handling in Java implies reading from and writing data to a file. The File class from the java.io package, allows us to work with different formats of files. In order to use the File class, you need to create an object of the class and specify the filename or directory name.

For example:

// Import the File class
import java.io.File

// Specify the filename
File obj = new File("filename.txt"); 

Java uses the concept of a stream to make I/O operations on a file. So let’s now understand what is a Stream in Java.

What is a Stream?

In Java, Stream is a sequence of data which can be of two types.

1. Byte Stream

This mainly incorporates with byte data. When an input is provided and executed with byte data, then it is called the file handling process with a byte stream.

2. Character Stream

Character Stream is a stream which incorporates with characters. Processing of input data with character is called the file handling process with a character stream.

Now that you know what is a stream, let’s dive deeper into this article on File Handling in Java and know the various methods that are useful for operations on the files like creating, reading and writing.

Java File Methods

Below table depicts the various methods that are used for performing operations on Java files.

MethodTypeDescription
canRead()BooleanIt tests whether the file is readable or not
canWrite()BooleanIt tests whether the file is writable or not
createNewFile()BooleanThis method creates an empty file
delete()BooleanDeletes a file
exists()BooleanIt tests whether the file exists
getName()StringReturns the name of the file
getAbsolutePath()StringReturns the absolute pathname of the file
length()LongReturns the size of the file in bytes
list()String[]Returns an array of the files in the directory
mkdir()BooleanCreates a directory

Let’s now understand what are the various file operations in Java and how to perform them.

File Operations in Java

Basically, you can perform four operations on a file. They are as follows:

    1. Create a File
    2. Get File Information
    3. Write To a File
    4. Read from a File

Now, let’s get into the details of each of these operations

1. Create a File

In this case, to create a file you can use the createNewFile() method. This method returns true if the file was successfully created, and false if the file already exists.

Let’s see an example of how to create a file in Java.

package FileHandling;

 // Import the File class
import java.io.File;

// Import the IOException class to handle errors
import java.io.IOException; 

public class CreateFile {
public static void main(String[] args) {
try {
// Creating an object of a file
File myObj = new File("D:FileHandlingNewFilef1.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();
}
}
}

In the above code, a file named NewFilef1 gets created in the specified location. If there is an error, then it gets handled in the catch block. Let’s check the output on executing the above code:

Output:

File created: NewFilef1.txt

Having understood this, let’s see how to get File information.

2. Get File information

Let’s see how to get file information using various methods with the help of below example code

package FileHandling;
import java.io.File; // Import the File class

public class FileInformation {
public static void main(String[] args) {
 // Creating an object of a file
File myObj = new File("NewFilef1.txt");
if (myObj.exists()) {
 // Returning the file name
System.out.println("File name: " + myObj.getName());

// Returning the path of the file 
System.out.println("Absolute path: " + myObj.getAbsolutePath());   

// Displaying whether the file is writable
System.out.println("Writeable: " + myObj.canWrite());  

// Displaying whether the file is readable or not
System.out.println("Readable " + myObj.canRead());  

// Returning the length of the file in bytes
System.out.println("File size in bytes " + myObj.length());  
} else {
System.out.println("The file does not exist.");
}
}
}

When you execute the above program, you will get the file information as shown in the output below:

Output:

File name: NewFilef1.txt
Absolute path: D:FileHandlingNewFilef1.txt
Writable: true
Readable true
File size in bytes 52

This is how you need to write a program to get the information of the specific file. Now let’s move further and see two more operations on the file. i.e. read and write operations.

3. Write to a File

In the following example, I have used the FileWriter class together with its write() method to write some text into the file. Let’s understand this with the help of a code.

package FileHandling;

// Import the FileWriter class
import java.io.FileWriter; 

// Import the IOException class to handle errors
import java.io.IOException; 

public class WriteToFile {
public static void main(String[] args) {
try {
FileWriter myWriter = new FileWriter("D:FileHandlingNewFilef1.txt");
 // Writes this content into the specified file
myWriter.write(Java is the prominent programming language of the millenium!"); 

// Closing is necessary to retrieve the resources allocated
myWriter.close(); 
System.out.println("Successfully wrote to the file.");
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
}

Output:

Successfully wrote to the file

When you run the file, the above text, “Java is the prominent programming language of the millennium!” will be entered in the file that you have created. You can cross check it by opening the file in the specified location.

Now let’s move further and understand the last operation on the file, i.e. Read a file

4. Read from a File

In the following example, I have used the Scanner class to read the contents of the text file.

package FileHandling;

// Import the File class
import java.io.File; 

// Import this class to handle errors
import java.io.FileNotFoundException; 

// Import the Scanner class to read text files
import java.util.Scanner; 

public class ReadFromFile {
public static void main(String[] args) {
try {
// Creating an object of the file for reading the data
File myObj = new File("D:FileHandlingNewFilef1.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();
}
}
}

When you execute the above program, it will display the content present in the given file.

Output:

Java is the prominent programming language of the millennium!

That’s how it works. So, this was all about the various file operations in Java. With this, we come to an end of this article on File Handling in Java. I hope you found it informative. If you wish to learn more, you can check out our other Java Blogs as well.

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Got a question for us? Please mention it in the comments section of this “File Handling in Java” article and we will get back to you as soon as possible.

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