Java – the sum of all numbers for a given positive number

Method returns that if you enter a number, assuming 345, the output should be 3 4 5 = 12 – > 1 2 = 3 What did I do wrong here?

public class DigitSum
 {
    int  Sum=0;

    public int compute( int MethParam )
    {
        int rem = MethParam%10; 
        Sum+=rem;        

        MethParam = MethParam/10; 
        if(MethParam>10)
            compute(MethParam);

        return Sum+MethParam;  
    }

  public static void main(String[] args)
  {
    DigitSum ds  = new DigitSum();
    System.out.println(ds.compute(435));
  }
}

Solution

O (1) algo is the sum of numbers:

Taking the modulus 9 of any number will return the sum of the numbers of that number until a single number is obtained

If the number is a multiple of 9, the sum will be 9

One liner:

public int sumDigit(int n){
    return (n%9 == 0 && n != 0) ? 9 : n%9;
}

Alternative implementation:

public int sumDigit(int n){

      int sum = n % 9;
      if(sum == 0){
          if(n > 0)
               return 9;
      }
      return sum;
}