Use Set
Interface to add the phone numbers to avoid duplicate.
Set<String> uniques = new HashSet<String>();
Check this simple example
public static void main(String[] args) {
Set<String> uniques = new HashSet<String>();
Set<String> dups = new HashSet<String>();
for (String a : args)
if (!uniques.add(a))
dups.add(a);
// Destructive set-difference
uniques.removeAll(dups);
System.out.println("Unique words: " + uniques);
System.out.println("Duplicate words: " + dups);
}
from this link ... http://docs.oracle.com/javase/tutorial/collections/interfaces/set.html