Integer Manipulation

[joebar]

Hello,

I need a method to manipulate an Integer. The input is an integer, I don't know how many digits, e.g. Input could be

160345 or
12947583749

Now I need the first 2 or 3 digits of that number, if I need 2 or 3 digits depends on the value. In the example above the method should return

160 for the first number, and 12 for the second number. Of course I can convert to a string and do a if-then-else ladder to figure out what I need, is there a better way?

Regards,
J.

[dlorde]

If the number of digits you select depends on the numeric value, I don't see any alternative to an 'if...else..' You haven't said how the digit selection depends on the value, so I can't suggest anything else.

A prudent question is one-half of wisdom...
F. Bacon

[joebar]

for example:

starts with
20
23
40

then take the frist 2 digits

when starts with
21
50
then take the first 3 digits

for everything else ignore the input.

[Filobel]

Not sure if it's the best way to do it, but you could do something like

public class MyClass
{
      TreeSet<Integer> two_numbers;
      TreeSet<Integer> three_numbers;

      MyClass(){
             two_numbers = new TreeSet<Integer>();
             two_numbers.add(20);
             two_numbers.add(23);
             //etc.

             three_numbers = new TreeSet<Integer>();
             three_numbers.add(21);
             //etc.
       }

      //I'm gonna return -1 if the number is ignored.
      int getFirstNumbers(int number)
      {
            if(number < 10)
                 return -1;

            if(number < 100){
                 if(two_numbers.contains(number))
                       return number;
                 else return -1;
            }
            
             while(number > 999)
                    number = (int)(number/10);
             int first2 = (int)(number/10);
             if(two_numbers.contains(first2))
                   return first2;
             if(three_numbers.contains(first2))
                   return number;
             return -1;
      }
}

[dlorde]

Meh... if the selection doesn't depend on the absolute value, but just on the leading digits, I'd be inclined to convert to a String and avoid any messy and unnecessary division:

String getDigits(Integer input) {

    // this map should probably be a class member and filled elsewhere
    Map<String, Integer> digitMap = new HashMap<String, Integer>();
    digitMap.put("20", 2);
    digitMap.put("23", 2);
    digitMap.put("40", 2);
    digitMap.put("21", 3);
    digitMap.put("50", 3);

    String inStr = input.toString();

    Integer count = digitMap.get(inStr.substring(0,2));

    if (count == null || inStr.length() < count) {
        return "";  // or null, or better still, throw an exception
    }
    return inStr.substring(0, count);    
}

Note: limited error handling included.

Weeks of programming can save you hours of planning...
Anon.