Input & Output in Java

In Java, input and output (I/O) operations are performed using the java.io package, which provides a set of classes and methods for reading data from input sources and writing data to output destinations. Here are some examples of how to use input and output in Java:

1. Reading Input

To read input from the user, you can use the Scanner class, which provides methods for reading different data types. Here is an example of how to read a string from the user:

import java.util.Scanner;

public class ReadInput {
    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 + "!");
    }
}

In this example, we create a new Scanner object to read input from the standard input stream (System.in). We then use the nextLine() method to read a line of text from the user and store it in a String variable called name.

2. Writing Output

To write output in Java, you can use the System.out object, which represents the standard output stream. Here is an example of how to write a message to the console:

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

In this example, we use the println() method of the System.out object to write a message to the console.

3. Reading and Writing Files

To read and write files in Java, you can use the File and FileReader or FileWriter classes. Here is an example of how to read the contents of a file and write them to another file:

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileIO {
    public static void main(String[] args) {
        try {
            File inputFile = new File("input.txt");
            FileReader reader = new FileReader(inputFile);
            int ch;
            StringBuilder content = new StringBuilder();
            while ((ch = reader.read()) != -1) {
                content.append((char) ch);
            }
            reader.close();
            File outputFile = new File("output.txt");
            FileWriter writer = new FileWriter(outputFile);
            writer.write(content.toString());
            writer.close();
            System.out.println("File copied successfully!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In this example, we create a File object to represent the input file, and a FileReader object to read the contents of the file. We then use a StringBuilder object to build a String containing the contents of the file. We create another File object to represent the output file, and a FileWriter object to write the contents of the StringBuilder to the file. We then close the input and output streams, and print a message to the console indicating that the file was copied successfully.