java.io Package

The java.io package provides classes and interfaces for reading data from various sources and writing data to different destinations. It includes classes for file handling, input and output streams, readers, writers, and other input/output operations.

In this chapter, you will learn about the java.io package and the commonly used classes and interfaces provided for input and output operations.

What is java.io Package?

The java.io package is a standard Java package that provides classes and interfaces for performing input and output operations. It can be used to read data from sources such as files and other input streams and to write data to files and other output streams.

The package contains classes for working with byte streams, character streams, files, buffered input and output, object serialization, and other I/O operations.

Classes and Interfaces in java.io Package

The java.io package contains several classes and interfaces for performing input and output operations. Some commonly used classes and interfaces are discussed below.

Byte Streams and Character Streams

The java.io package provides two main types of streams for handling data: byte streams and character streams. Byte streams are used to read and write raw byte data, while character streams are used to read and write text data.

InputStream and OutputStream are the main base classes for byte streams. Reader and Writer are the main base classes for character streams.

Example

In the following example, FileOutputStream writes byte data to a file, while FileWriter writes character data to another file.

import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;

public class StreamExample {
    public static void main(String[] args) throws IOException {

        FileOutputStream byteStream = new FileOutputStream("byte.txt");
        byteStream.write(65);
        byteStream.close();

        FileWriter characterStream = new FileWriter("character.txt");
        characterStream.write("Hello Java");
        characterStream.close();

        System.out.println("Data written successfully.");
    }
}

Output:

Data written successfully.

File Handling Using java.io

The java.io package provides classes for working with files and directories. The File class can be used to check whether a file or directory exists, obtain file information, create directories, and perform operations such as renaming and deleting files.

Classes such as FileInputStream, FileOutputStream, FileReader, and FileWriter can also be used to read from and write to files.

Example

In the following example, the File class is used to check whether a file exists and display its name and path.

import java.io.File;

public class FileExample {
    public static void main(String[] args) {
        File file = new File("example.txt");

        System.out.println("File Name: " + file.getName());
        System.out.println("File Path: " + file.getAbsolutePath());
        System.out.println("File Exists: " + file.exists());
    }
}

Output:

File Name: example.txt
File Path: C:\Java\example.txt
File Exists: false

Exception Handling in java.io

Input and output operations can cause exceptions such as IOException. Java provides exception handling mechanisms to handle errors that may occur while reading, writing, or closing I/O resources.

The try-catch statement can be used to handle I/O exceptions. The try-with-resources statement can also be used to automatically close resources after they are used.

Example

In the following example, FileReader is used to read a file, and the IOException is handled using a try-catch block.

import java.io.FileReader;
import java.io.IOException;

public class IOExceptionExample {
    public static void main(String[] args) {

        try {
            FileReader reader = new FileReader("example.txt");
            int data = reader.read();

            System.out.println("Character: " + (char) data);

            reader.close();
        } catch (IOException e) {
            System.out.println("An I/O error occurred.");
        }
    }
}

Output:

An I/O error occurred.