Extract numbers from String and add them

Question

For my school, I have to create an add function which can add 2 numbers.

Example: /add 6 4
Solution: 10

This is my code at the moment, which lets me do that, but only with at maximum /add 9 9 :

String stString = message_text;
String number = stString.replaceAll("[^0-9]", "");
int numArr[] = new int[2];
for (int i = 0; i<2; i++) {
    numArr[i] = Integer.parseInt(String.valueOf(number.charAt(i)));
}

int sum = IntStream.of(numArr).sum();

I need a way to be able to make it that I could use /add 14 23 or so.

Answer 1

Why don't you use split like this:

String[] myValues = stString.split(" ");

And after that get the values by myValues[1] and myValues[2]

Answer 2

Can't write your homework for you, but look at your logic. If you only read a single character, you can only ever have a single digit.

Parse for multidigit inputs instead of using charAt() . Take a few extra lines of code to collect and build your inputs. Try String.substring() or String.split() and work from there.

Answer 3

Since you are already using streams, you could make a 1-liner stream-only solution:

int sum = Stream.of(stString.split(" ")).
    skip(1).
    mapToInt(Integer::parseInt).
    sum();

Answer 4

Your problem is that you are complicating it too much with replace() , String.valueOf() and IntStream.of(numArr).sum() , and then you limit your program to read only one character, so your numbers will be always composed of only one digit.

Solution:

You just need to use .split() method and pass to it a space as delimiter:

String stString = "/add 64 10";
int a = Integer.parseInt(stString.split(" ")[1]);
int b = Integer.parseInt(stString.split(" ")[2]);
System.out.println(a+b); //will print 74

Answer 5

The problem with your approach is that you confuse the index of the required numbers in the String with their actual index in the String . Essentially you want two numbers but you always look for two consecutive digits after your replacement.

One way to work around this would be to use a simple regular expression to fetch 1+ digit sequences and collect them.

For instance:

String[] test = {
        "/add 1 2",
        "/add 22 20"
    };
Pattern digits = Pattern.compile("\\d+");
for (String s: test) {
    // parsing after /add
    String sequence = s.substring(4);
    // matching digits
    Matcher m = digits.matcher(sequence);
    // finding as many numbers as possible - you can always hard-limit to 2 if needed
    long sum = 0;
    while (m.find()) {
        // no need to check parsing, it will always be integer figures at this point
        sum += Integer.parseInt(m.group());
    }
    System.out.println(sum);
}

Output

3
42

Answer 6

You can use split string instead and then convert the fragments into numbers:

    String stString = "/add 14 56";
    String[] fragments = stString.split(" ");
    int sum = 0;
    // Start from fragment 1 assuming that fragment 0 is "/add"
    for (int i = 1; i < fragments.length; i++)
        try {
            sum += Integer.valueOf(fragments[i]);
        } catch (Exception e) {
            System.err.println("Something went wrong converting the strings into integers.");
            System.err.println("Please check the input string.");
            System.err.println("\n");
            e.printStackTrace();
            break;
        }