Java's File()

Java provides a class File to handle file IO. Here is a basic program to print the contents of an input file, and write the contents of an input file to an output file:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
 
public class Files {
	public static void main(String[] args) throws FileNotFoundException, IOException {
		File f1 = new File("input.txt");
	// System.out.println(f1.getAbsolutePath());
	// System.out.println(f1.getCanonicalPath());
	// File f2 = new File(f1.toPath());
	Scanner in = new Scanner(f1);
		while (in.hasNextLine()){
			System.out.println(in.nextLine());
		}
	}
}

Note that this program does not use try/catch, it just throws FileNotFoundException, IOException.

IMPORTANT: If the file path inside File() is relative, Java will only see that file if java is invoked in the same directory as the source file. If our source file Files.java is at /home/user/programs/java/Files.java, we must execute javac Files.java and java Files inside the java directory. If you use VSCode, java is not executed in the project directory (see the command VSCode runs when you use the play button).