How to use FileReader and FileWriter using Java (MP 10)

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package main;

/**
 *
 * @author markjasongalang
 */
import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        FileReader file_reader_object = new FileReader("/Users/markjasongalang/Desktop/JAVA-CP/Main/src/main/test.txt");
        int file_iterator = 0;
        String data = "";
        while ((file_iterator = file_reader_object.read()) != -1) {
            if ((char) file_iterator == ' ') {
                data += "_";
            } else {
                data += ((char) file_iterator);
            }
        }
        file_reader_object.close();
        try {
            FileWriter file_writer_object = new FileWriter("/Users/markjasongalang/Desktop/JAVA-CP/Main/src/main/test.txt");
            file_writer_object.write(data);
            file_writer_object.close();
        } catch (Exception e) {
            System.out.println(e);
        }
        System.out.println("Successfully read and written in text file");
    }
}