Multiplication two string in java

package com.swain.cell;

public class Div {

public String Mul (int a, int b){

int sum=a*b;

System.out.println("Sum="+sum);

return "temp="+sum;

}

public static void main (String args[]){

Div p=new Div();

String str=null;

str=p.Mul(15, 5);

System.out.println(str);

}

}