public class Test {
public static void main(String[] args) {
int a = 1203;

int sum = 0;
while(a / 10 != 0){
sum += a % 10;
a = a / 10;
}

sum = sum + a;

System.out.println("各位数字之和为" + sum);
}
}
-----------testing
各位数字之和为6