Question:

Consider the following scenario:

You have been given a task to create a Java program that reads a text file, performs some operations, and writes the result to a new file. As part of this task, you need to utilize the file classes provided in Java. Write a program that reads a text file named "input.txt", calculates the frequency of each word present in the file, and writes the result to a new text file named "output.txt".

Write a Java program that accomplishes the above task. Your program should satisfy the following requirements:

• Use the appropriate file classes in Java to read from and write to files.
• Implement a method named calculateWordFrequency(String fileName) that takes the name of the input file as a parameter and returns a HashMap<String, Integer> containing the frequency of each word.
• Implement a method named writeToFile(HashMap<String, Integer> wordFrequency, String fileName) that takes the word frequency map and the name of the output file as parameters, and writes the word frequency data to the output file.
• Handle any potential exceptions that may occur.

Provide the complete implementation of the Java program.

Answer:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class WordFrequencyCalculator {

    public static void main(String[] args) {
        String inputFileName = "input.txt";
        String outputFileName = "output.txt";
        try {
            HashMap<String, Integer> wordFrequency = calculateWordFrequency(inputFileName);
            writeToFile(wordFrequency, outputFileName);
            System.out.println("Word frequency calculation completed and written to " + outputFileName);
        } catch (FileNotFoundException e) {
            System.out.println("Input file not found: " + inputFileName);
        } catch (IOException e) {
            System.out.println("An error occurred while writing to the output file: " + outputFileName);
        }
    }

    public static HashMap<String, Integer> calculateWordFrequency(String fileName) throws FileNotFoundException {
        HashMap<String, Integer> wordFrequency = new HashMap<>();
        File inputFile = new File(fileName);

        // Read the input file
        Scanner scanner = new Scanner(inputFile);
        while (scanner.hasNext()) {
            String word = scanner.next();
            wordFrequency.put(word, wordFrequency.getOrDefault(word, 0) + 1);
        }
        scanner.close();

        return wordFrequency;
    }

    public static void writeToFile(HashMap<String, Integer> wordFrequency, String fileName) throws IOException {
        FileWriter writer = new FileWriter(fileName);
        for (Map.Entry<String, Integer> entry : wordFrequency.entrySet()) {
            writer.write(entry.getKey() + ": " + entry.getValue() + "\n");
        }
        writer.close();
    }
}

Explanation:

1. The program starts by declaring the necessary import statements including the file classes.
2. The WordFrequencyCalculator class contains the main method where the program execution begins. It sets the input and output file names, and then proceeds to call the calculateWordFrequency and writeToFile methods to perform the required operations.
3. The calculateWordFrequency method takes the input file name as a parameter and returns a HashMap<String, Integer> representing the frequency of each word in the file. It opens the input file using a Scanner and uses a while loop to read each word from the file. For each word, it updates the frequency in the wordFrequency map using the getOrDefault method to handle both new and existing words efficiently.
4. The writeToFile method takes the word frequency map and the output file name as parameters. It opens the output file using a FileWriter and uses a for loop to iterate over each entry in the map. It writes the word and frequency to the output file using the write method of the FileWriter.
5. The main method handles potential FileNotFoundException and IOException exceptions that may occur during file input/output operations. It catches these exceptions and prints an appropriate error message.
6. The program completes by printing a message indicating the completion of the word frequency calculation and writing to the output file.

Make sure to have the "input.txt" file available in the same directory as the Java program before running the program. The word frequency data will be written to the "output.txt" file.