public class StringMultiplication {
public static void main(String[] args) {
    String number1 = "17";
    String number2 = "15";

    char[] n1 = number1.toCharArray();
    char[] n2 = number2.toCharArray();

    int result = 0;
    for (int i = 0; i < n1.length; i++) {
        for (int j = 0; j < n2.length; j++) {
            result += (n1[i] - '0') * (n2[j] - '0')* (int) Math.pow(10, n1.length * 2 - (i + j + 2));
        }
    }
    System.out.println(result);
}
}

import java.math.*;

public class StringMultiplication {
public static void main(String[] args) {
    String number1 = "17";
    String number2 = "15";

    BigInteger num1=new BigInteger(number1);
    BigInteger num2=new BigInteger(number2);
    BigInteger result=num1.multiply(num2);
    System.out.println(result);
}
}