Java Input and Output Operations

Java's Input and Output (I/O) system enables communication between a program and the external world, such as reading input from a user, files, or other sources and outputting information to the console or files. The java.io package provides a comprehensive set of classes for handling I/O operations.

1. Input Operations

Input operations allow you to read data from external sources, such as the keyboard, files, or network streams. Below are common ways to handle input in Java:

Reading Input from Console

Class Used: Scanner (from java.util package)

Example:

import java.util.Scanner;

public class ConsoleInputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter your name: ");
        String studentname = scanner.nextLine(); // Captures an entire line of input
        
        System.out.print("Enter your age: ");
       
        int studentage = scanner.nextInt(); // Retrieves an integer from input

        System.out.println("Name: " + name + ", Age: " + age);
        scanner.close();
    }
}

Explanation:

nextLine() reads a full line of text.
nextInt() reads an integer.
Always close the Scanner object to free resources.

2. Output Operations

Output operations enable writing data to external destinations, such as the console or a file.

Writing Output to Console

Class Used: System.out

Example:

public class ConsoleOutputExample {
    public static void main(String[] args) {
        System.out.println("Hello, World!");  // Displays a message followed by a newline
        System.out.print("This is a test.");  // Prints without adding a newline
        System.out.printf("Formatted number: %.2f", 123.456); // Outputs a formatted number
    }
}

Explanation:

println() appends a newline after displaying the output.
print() keeps the output on the same line without adding a newline.
printf() is used for formatted output.

Writing Output to a File

Class Used: FileWriter and BufferedWriter

Example:

import java.io.*;

public class FileOutputExample {
    public static void main(String[] args) {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"))) { // Uses a buffered writer for file output
            writer.write("This is a test message.");
            writer.newLine();  // Adds a new line
            writer.write("File writing in Java is simple!");
        } catch (IOException e) {
            System.out.println("File writing error: " + e.getMessage());
        }
    }
}

Explanation:

FileWriter writes character-based data to a file.
BufferedWriter enhances performance by buffering data before writing to a file.

3. Advanced I/O Operations

Java also supports advanced I/O through classes like DataInputStream, DataOutputStream, ObjectInputStream, and ObjectOutputStream for handling primitive data types or objects.

Example: Writing and Reading Binary Data

import java.io.*;

public class BinaryIOExample {
    public static void main(String[] args) {
        // Writing binary data
        try (DataOutputStream dos = new DataOutputStream(new FileOutputStream("data.bin"))) { // Writes binary data to a file
            dos.writeInt(42);  // Writes an integer
            dos.writeDouble(3.14159);  // Writes a double
        } catch (IOException e) {
            System.out.println("Error occurred while writing binary data: " + e.getMessage());
        }

        // Reading binary data
        try (DataInputStream dis = new DataInputStream(new FileInputStream("data.bin"))) { // Reads binary data from a file
            int number = dis.readInt();  // Reads an integer
            double value = dis.readDouble();  // Reads a double
            System.out.println("Number: " + number + ", Value: " + value);
        } catch (IOException e) {
            System.out.println("Error reading binary data: " + e.getMessage());
        }
    }
}

Explanation:

DataOutputStream and DataInputStream handle primitive data types in binary format.
Files generated by this method are not human-readable.

Summary of Common I/O Classes

Class Name	Purpose
`Scanner`	Reading input from console or files
`BufferedReader`	Efficient reading of text data
`FileReader`	Reading character-based data from files
`FileWriter`	Writing character-based data to files
`DataInputStream`	Reading primitive data in binary form
`DataOutputStream`	Writing primitive data in binary form
`ObjectInputStream`	Reading serialized objects
`ObjectOutputStream`	Writing serialized objects

Previous Next

HTML

JAVASCRIPT

CSS

PYTHON

JAVA

Java Input and Output Operations