I/O

File Input/Output (I/O) operations are used to read data from files or write data to files. In Java, file I/O operations are performed using classes from the java.io package. In this tutorial, we will learn how to read from and write to files in Java.

File I/O

Reading from a File

To read data from a file in Java, you can use the FileInputStream and BufferedReader classes. The FileInputStream class is used to read bytes from a file, and the BufferedReader class is used to read text from a character-input stream. Here is an example of reading data from a file:

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

public class ReadFile {
    public static void main(String[] args) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader("input.txt"));
            String line = reader.readLine();
            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above example, we use the BufferedReader class to read data from a file named input.txt. We read each line from the file using the readLine() method and print it to the console.

Writing to a File

To write data to a file in Java, you can use the FileOutputStream and BufferedWriter classes. The FileOutputStream class is used to write bytes to a file, and the BufferedWriter class is used to write text to a character-output stream. Here is an example of writing data to a file:

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class WriteFile {
    public static void main(String[] args) {
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"));
            writer.write("Hello, World!");
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above example, we use the BufferedWriter class to write the text “Hello, World!” to a file named output.txt.

User I/O

Reading User Input

To read user input from the console in Java, you can use the Scanner class. The Scanner class is used to read input from various sources, including the console. Here is an example of reading user input:

import java.util.Scanner;

public class ReadUserInput {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter your name: ");
        String name = scanner.nextLine();
        System.out.println("Hello, " + name + "!");
        scanner.close();
    }
}

In the above example, we use the Scanner class to read the user’s name from the console and print a greeting message.

Writing Output

To write output to the console in Java, you can use the System.out.println() method. This method is used to print text to the console. Here is an example of writing output to the console:

public class WriteOutput {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

In the above example, we use the System.out.println() method to print the text “Hello, World!” to the console.