I have an array which looks like this:
array = { Person1, Person2, Person3, Person1, Person2, Person3};
Now how can I get an int with the total count of unique Persons? That means a Person which was already counted, shouldn't be counted again.
In the give example above should return the int value of 3
int uniq = 3;
How can I do this task?
If all you want is the size, this is a correct version of one of the other answers:
Set<Person> set = new HashSet<Person>(Arrays.asList(array));
int count = set.size();
This assumes that either your Person type has an equals method that will tell you whether two persons are the same, or if there's no equals, the default equals is OK (the default returns true if the references are equal).
P.S.: if you've defined your own Person in equals, you must also define hashCode or else this solution won't work. hashCode must be defined so that if two Persons are equal then they also have the same hash code. See What issues should be considered when overriding equals and hashCode in Java?.
the easiest way is to avoid doublon when you add the person in your array. To do that, when you add a Person in the array, you go through all the array and verify that you don't already have it :)
If you need to have the doublon in the list, then you should create a tempArray and only add the different person in this new array like described in the other method, so in the end you will have your good number in the tempArray.size()
Try:
List<Person> uniqueList = new ArrayList<Person>(new LinkedHashSet<Person>( array.asList() ).sort() );
uniqueList.size(); //Number of unique objects
LinkedHashSet doesn't have a sort method; (2) you couldn't even do a sort if the element types aren't Comparable, and we have no idea whether the element type has ordering functions defined; (3) if all he wants is the size, then sort would be pointless anyway.asList method. The correct call is Arrays.asList(array).
array[0] == array[3]would be true, in the above example)? Or have you redefinedequalsfor yourPersonclass? Or are you using some other method to test whether two persons are the same?