FullBuisnessOperation_Monad.java

public abstract Result<Integer> readIntFromFile(String file);

public Result<Integer> adjustValue(Integer value) {
    if (value > 5) {
        Result.error("Value " + value + " should no be greater than 5");
    }

    return Result.ok(5 - value);
}

public Double calculateAverage(Integer val1, Integer val2) {
    return (val1 + val2)/2d;
}

/**
 * Read ints from two files, Adjust the first one and then calculate average.
 * Returns a Result wrapping the positive outcome or any error.
 */
public Result<Double> businessOperation(String fileName, String fileName2) {
    Result<Integer> adjustedValue = readIntFromFile(fileName)
                                    .flatMap(this::adjustValue)
    
    return adjustedValue.flatMap( val1 ->
           readIntFromFile(fileName2).flatMap( val2 ->
           Result.ok(calculateAverage(val1, val2))
    ));
}