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File Handling in Java – How to Work with Java Files

File handling in Java refers to working with files stored on a computer’s filesystem. It involves reading from files, writing to files, creating new files, deleting files, and manipulating file attributes. To put it simply, file handling is the process of reading and writing data into a file.

In Java, file handling is primarily achieved through classes and interfaces in the ‘java.io’ package and ‘java.nio.file, introduced in the Java 7 version. This article will cover the basics of file handling in Java, including reading, writing, creating and deleting files.

Why is File Handling Required?

File handling in Java programming is required for several reasons;

• Data Persistence: File handling is the backbone of data persistence in Java. It allows data to be stored persistently on a disk and ensures that data is not lost when the program terminates, or the computer is turned off. This is a critical aspect for applications that must maintain user preferences, application state, or handle large datasets.

• Data Sharing: File enables data sharing between different programs or systems. For example, documents, image configuration files, and more can be transferred between computers.

• Data Backups: Files can be used to create backups of important data, ensuring that data can be restored in case of accidental deletion, hardware failure, or other disasters.

• Logging and Debugging: Files are often used to log events and errors and debug information during program execution. This helps developers diagnose issues and improve software reliability.

Program

 Output

The stream concept is used to perform I/O operations on a file. Let’s learn about it in Java.

Stream in Java

Streams in Java are an integral part of the Java I/O (Input/Output) system, providing a way to read from and write to different kinds of I/O sources. Java provides two main types of streams. Byte Stream and Character Streams.

Input Stream

The Java InputStream class is the superclass of all input streams. It reads data from numerous input devices, such as the keyboard, network, etc. InputStream is an abstract class.

The InputStream’ class in Java is a part of the ‘java.io’ package and serves as the superclass for all classes representing an input stream of bytes.

There are several subclasses of the InputStream class, which are as follows.

1. AudioInputStream
2. ByteArrayInputStream
3. FileInputStream
4. FilterInputStream
5. StringBufferInputStream
6. ObjectInpuStream

Creating an InputStream

InputStream ob = new FileInputStream() ;

In the above line, we have created inputStream using FileInputStream class.

Methods of InputStream

Output Stream

The “OutputStream” class in Java is part of the java.io package and is an abstract class representing an output stream of bytes. It is the superclass of all classes representing an output stream of bytes and is a key part of Java’s I/O system.

There are several subclasses of the OutputStream class, which are as follows.

1. ByteArrayOutputStream
2. FileOutputStream
3. StringBufferOutputStream
4. ObjectOutputStream
5. DataOutputStream
6. PrintStream

Creating an OutputStream

OutputStream ob = new FileOutputStream() ;

In the above line, An Output stream is created using FileOutputStream

Methods of OutputStream

There are two types of streams in the Java programming language.

Byte Stream: A byte stream reads or writes byte data. It is also divided into two types, which are as follows.

• Byte Input Stream: Byte Stream reads byte data from different devices.
• Byte Output Stream: It writes byte data on different output devices.

Character Stream: 

This character stream is used to read or write character data. Character stream is again subdivided into two types, which are as follows.

• Character Input Stream: A character stream reads character data from different devices.
• Character Output Stream:  A character stream outputs character data from different devices.

Java File Class Methods

The following table defines Java File Methods:

File Operation in Java

The following are several operations that can be performed on a file in Java.

• Create a File
• Read from a file
• Write to a file
• Delete a file

Now, let us study each of the above operations in detail.

Create a File

• We can use the createNewfile() method defined in the java io output package to create a file in Java.
• If the file is successfully created, it will return a Boolean value of true, and false if it already exists.

The following program demonstrates how to create a file in Java language.

Program

Output

Read From a File:

We can also read content from a file using the Scanner class. The program below demonstrates how to read content from a Java file.

Output

Write to a File:

We can also write text into a file using the FileWriter class in Java. There is a write() method to do this. The following program demonstrates the FileWriter Class example.

Program

Output

Delete a File

To delete a file from the computer system, we can use the delete () method. The following demonstrates how to delete a file in Java.

Program

Output

In this article, we learned about File handling in Java. It is a fundamental skill for any developer, enabling the creation, manipulation, and management of files and directories by leveraging the classes and methods in the ‘java.io’ package. You can perform tasks such as reading from and writing to files, managing directories, and handling exceptions effectively.  Whether dealing with simple text files or complex file structures, Understanding file handling in Java is essential for developing comprehensive and high-performing software solutions.