public static String getSmallestAndLargest(String s, int k) 
    {
        int e,d=s.length()-k+1;
        String smallest="",largest="";
        String[] a=new String[d];
        try
        {
            for(int i=0;i<d;i++)
            {
                a[i]="";
                for(int j=i;j<(i+k);j++)
                    a[i]+=s.charAt(j);
            }
            smallest=a[0];
            largest=a[0];
            for(int i=0;i<a.length;i++)
            {
                e=largest.compareTo(a[i]);
                if(e<0)
                    largest=a[i];
                e=smallest.compareTo(a[i]);
                if(e>0)
                smallest=a[i];
            }
       }catch(Exception yti){}
        return smallest + "\n" + largest;
    }