PerformStringShifts.java

class PerformStringShifts {
  
    public String stringShift(String s, int[][] shift) {
        int shiftNumber = 0;
        for (int[] shiftOperation : shift) {
            if (shiftOperation[0] == 1) {
                shiftNumber += shiftOperation[1];
            } else {
                shiftNumber -= shiftOperation[1];
            }
        }
        char[] charArray = s.toCharArray();
        shiftNumber %= charArray.length;
        if (shiftNumber < 0) {
            shiftNumber += charArray.length;
        }
        shiftArray(charArray, shiftNumber);
        return new String(charArray);
    }

    private void shiftArray(char[] charArray, int shiftNumber) {
        reverse(charArray, 0, charArray.length - 1);
        reverse(charArray, 0, shiftNumber - 1);
        reverse(charArray, shiftNumber, charArray.length - 1);
    }

    private void reverse(char[] charArray, int left, int right) {
        while (left < right) {
            swap(charArray, left++, right--);
        }
    }

    private void swap(char[] charArray, int from, int to) {
        char c = charArray[from];
        charArray[from] = charArray[to];
        charArray[to] = c;
    }
        
}

Nicely done. I like how you created small methods, your code looks very clean.

One minor comment: would the if condition in line 14 ever be true? As far as I know the module operator will always return a positive value

Yes, it can be negative the % returns the same sign as the dividend