Question

I am attempting to sort an ArrayList based on the value of a long present within each object. After following various examples around the internet, I have come up with the following code but it is not sorting as desired (it seems to truncate parts of the object).

public static Comparator<Customer> compareSIN = 
         new Comparator<Customer>() {
            public int compare(Customer cust1, Customer other) {
               String sin1 = "" + cust1.sin;
               String sin2 = "" + other.sin;
               return sin1.compareTo(sin2);
            }
         };

Please advise me on what I am doing missing in the first snippet of code that is preventing me from sorting the objects properly.

Thanks!

Answer 1

From the title I assume Customer.sin is a long – and the problem is you are trying to compare them as Strings rather then by their numeric value.

(Example: 10000 is lexicographically smaller then 2 – so using Strings here is the fault)

You should use Long.compare() (Assuming java 7):

public static Comparator<Customer> compareSIN = 
         new Comparator<Customer>() {
            public int compare(Customer cust1, Customer other) {
               return Long.compare(cust1.sin,other.sin);
            }
         };