public static String getSmallestAndLargest(String str, int number) { String smallest = ""; String largest = "";

    for(int i=0;i<=str.length()-number;i++){
        int range = i + number;
        String subStringI = str.substring(i,range);
        if(subStringI.compareTo(largest)>0){
            largest=subStringI;
        }
        if(subStringI.compareTo(smallest)<0){
            smallest=subStringI;
        }
        if(i==0){
            smallest=subStringI;
        }
    }
    return smallest + "\n" + largest;
}