fileReaderWriter.java

FileReader file;
String line;
String lineSplited[];
int qtd = 0;
//  File Readding
file = new FileReader("C:\\Users\\user\\Desktop\\arquivo.txt");
BufferedReader reader = new BufferedReader(file);
FileWriter fileNew = new FileWriter("C:\\Users\\user\\Desktop\\arquivo_alterado.txt");
BufferedWriter writer = new BufferedWriter(fileNew);

while (qtd < 32561) {
    line = reader.readLine();
    lineSplited = line.split(",");
    //  Alter
    if (Integer.parseInt(lineSplited[0]) < 40) {
        lineSplited[0] = "<40";
    } else  lineSplited[0] = ">=40";
    if (Integer.parseInt(lineSplited[8]) < 40) {
        lineSplited[8] = "<40";
    } else  lineSplited[8] = ">=40";

    //  File Writting
    for (int i=0; i < lineSplited.length; i++) {
        if (i == lineSplited.length-1) {
            writer.write(lineSplited[i] + "\r\n");
        } else {
            writer.write(lineSplited[i] + ",");
        }
    }
    qtd++;
}
reader.close();
writer.close();