codejava.tech/content/courses/prog-intro/homeworks/sum/SumBigIntegerOctal/_index.md

title, weight

title	weight
SumBigIntegerOctal	6

Task

• Input data fits into BigInteger data type.
• Octal numbers ends with o.
• Class should be named SumBigIntegerOctal.

Solution

Let's change our parseNumber method code from SumLongOctal modification. Here's what it looked like

static long parseNumber(StringBuilder number) {
    if (!number.isEmpty()) {
        String numberString = number.toString();
        int numberStringLength = numberString.length();
        if (numberString.endsWith("o") || numberString.endsWith("O")) {
            return new BigInteger(
                number.substring(0, numberStringLength - 1),
                8
            ).longValue();
        } else {
            return Long.parseLong(numberString);
        }
    } else {
        return 0;
    }
}

First of all let's change the output type of our method to BigInteger.

static BigInteger parseNumber(StringBuilder number) {...}

Also in case of an empty number we can't just return 0 anymore because it doesn't have BigInteger data type. Instead we are going to return BigInteger.ZERO.

Here we can get rid of .longValue() because we just need straight BigInteger type.

return new BigInteger(number.substring(0, numberStringLength - 1), 8); // .longValue();

Also we change this

return Long.parseLong(numberString);

to this

return new BigInteger(numberString);

for the same reason. So the parseNumber will look like this

static BigInteger parseNumber(StringBuilder number) {
    if (!number.isEmpty()) {
        String numberString = number.toString();
        int numberStringLength = numberString.length();
        if (numberString.endsWith("o") || numberString.endsWith("O")) {
            return new BigInteger(
                number.substring(0, numberStringLength - 1),
                8
            );
        } else {
            return new BigInteger(numberString);
        }
    } else {
        return BigInteger.ZERO;
    }
}

Let's rework our main method as well. Here's what it looks like now

public static void main(String[] args) {
    int sum = 0;
    for (String argument : args) {
        StringBuilder number = new StringBuilder();
        for (char c : argument.toCharArray()) {
            if (!Character.isWhitespace(c)) {
                number.append(c);
            } else {
                sum += parseNumber(number);
                number = new StringBuilder();
            }
        }

        sum += parseNumber(number);
    }

    System.out.println(sum);
}

First of all, let's change the data type of sum to BigInteger like this

BigInteger sum = new BigInteger("0");

Important

Notice, we can't just do new BigInteger() (without any arguments) like we did with StringBuilder. We need to put the initial value as an argument like new BigInteger(String val).

So in this stage our code will look like this

// SumBigIntegerOctal.java

import java.math.BigInteger;

public class SumBigIntegerOctal {

    public static void main(String[] args) {
        BigInteger sum = new BigInteger("0");
        for (String argument : args) {
            StringBuilder number = new StringBuilder();
            for (char c : argument.toCharArray()) {
                if (!Character.isWhitespace(c)) {
                    number.append(c);
                } else {
                    sum += parseNumber(number);
                    number = new StringBuilder();
                }
            }

            sum += parseNumber(number);
        }

        System.out.println(sum);
    }

    static BigInteger parseNumber(StringBuilder number) {
        if (!number.isEmpty()) {
            String numberString = number.toString();
            int numberStringLength = numberString.length();
            if (numberString.endsWith("o") || numberString.endsWith("O")) {
                return new BigInteger(
                    number.substring(0, numberStringLength - 1),
                    8
                );
            } else {
                return new BigInteger(numberString);
            }
        } else {
            return BigInteger.ZERO;
        }
    }
}

And let's try to compile this

$ javac SumBigIntegerOctal.java
SumBigIntegerOctal.java:15: error: bad operand types for binary operator '+'
                    sum += parseNumber(number);
                        ^
  first type:  BigInteger
  second type: BigInteger
SumBigIntegerOctal.java:20: error: bad operand types for binary operator '+'
            sum += parseNumber(number);
                ^
  first type:  BigInteger
  second type: BigInteger
2 errors

Note

We can't use + operand with BigInteger data type. Instead we need to use BigInteger.add(BigInteger val).

So we will modify like so

// SumBigIntegerOctal.java

import java.math.BigInteger;

public class SumBigIntegerOctal {

    public static void main(String[] args) {
        BigInteger sum = new BigInteger("0");
        for (String argument : args) {
            StringBuilder number = new StringBuilder();
            for (char c : argument.toCharArray()) {
                if (!Character.isWhitespace(c)) {
                    number.append(c);
                } else {
                    sum = sum.add(parseNumber(number));
                    number = new StringBuilder();
                }
            }

            sum = sum.add(parseNumber(number));
        }

        System.out.println(sum);
    }

    static BigInteger parseNumber(StringBuilder number) {
        if (!number.isEmpty()) {
            String numberString = number.toString();
            int numberStringLength = numberString.length();
            if (numberString.endsWith("o") || numberString.endsWith("O")) {
                return new BigInteger(
                    number.substring(0, numberStringLength - 1),
                    8
                );
            } else {
                return new BigInteger(numberString);
            }
        } else {
            return BigInteger.ZERO;
        }
    }
}

And this code will pass all the tests!