Question

Write a program in Java that reads an input text file (named: input.txt) that has several lines of text and put those line in a data structure, make all lowercase letters to uppercase and all uppercase letters to lowercase and writes the new lines to a file (named: output.txt).

Answer 1

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

public class ChangeTextCase {

    public static void main(String[] args) {
        File file = new File("input.txt");
        try {
            Scanner fin = new Scanner(file);
            PrintWriter pw = new PrintWriter("output.txt");
            String line, modified;
            while (fin.hasNextLine()) {
                line = fin.nextLine();
                modified = "";
                for (int i = 0; i < line.length(); i++) {
                    if (Character.isLowerCase(line.charAt(i))) {
                        modified += Character.toUpperCase(line.charAt(i));
                    } else {
                        modified += Character.toLowerCase(line.charAt(i));
                    }
                }
                pw.println(modified);
            }
            System.out.println("Modified file is written to output.txt");
            pw.close();
            fin.close();
        } catch (FileNotFoundException e) {
            System.out.println(file.getAbsolutePath() + " is not found!");
        }
    }
}