Decode Ways - Secret Message [ZOHO]

                      Decode Ways - Secret Message

A top secret message string S containing letters from A-Z (only upper case letters) is encoded to numbers using the following mapping: 'A' -> 1, 'B' -> 2 and so on till Z -> '26'
The program has to print the total number of ways in which the received message can be decoded.

Input Format: The first line contains the string S containing numbers.

Output Format: The first line contains the number of ways in which S can be decoded.

Boundary Conditions: 1 <= Length of S <= 100

Example Input/Output 1:
Input:
123
Output:
3
Explanation:
1-A 2-B 3-C 12-L 23-W. Hence 123 can be decoded as ABC or AW or LC, that is in 3 ways.

Example Input/Output 2: 
Input:
1290
Output:
0

Code:

import java.util.*;

public class Hello {
    public static int num(String s){
 if(s==null||s.length()==0||s.charAt(0)=='0')
         return 0;
  if(s.length()==1)
               return 1;
   int[] dp=new int[s.length()];
   dp[0]=1;

   if(Integer.parseInt(s.substring(0,2))>26)
     {
         if(s.charAt(1)!='0')
             dp[1]=1;
         else
           dp[1]=0;
     }
    else
    {
       if(s.charAt(1)!='0')
            dp[1]=2;
        else
            dp[1]=1;
    }

    for(int i=2;i<s.length();i++)
        {
            if(s.charAt(i)!='0')
               dp[i]+=dp[i-1];
   int val=Integer.parseInt(s.substring(i-1,i+1));
           if(val<=26&&val>=10)
              dp[i]+=dp[i-2];
        }

    return dp[s.length()-1];

 }

public static void main(String[] args)
{
    Scanner sc=new Scanner(System.in);
    String st=sc.next();
    System.out.print(num(st));
}
}