prob_92_Euler

public class t {

    public static void main(String[] args) {
        int current_val = 0, counter = 0;

        for (int i = 1; i < 10000000; i++) {
            current_val = i;
            while (current_val != 1) {
                current_val = calculateSquares(current_val);
                if (current_val == 89) {
                    counter++;
                    break;
                }
            }
        }
        System.out.println(counter);
        
    }

    public static int calculateSquares(int num) {
        
        int result = 0;
        int current_digit = 0;
        while(num > 0) {
            current_digit = num % 10;
            num = (num - current_digit) / 10;
            result += current_digit * current_digit;
        }
        return result;

    }
    
}

This can run much faster if you didn't convert from int -> char -> int again, just use division to extract the digits from the number.