How to remove duplicates from a list?
Assuming you want to keep the current order and don't want a Set
, perhaps the easiest is:
List<Customer> depdupeCustomers =
new ArrayList<>(new LinkedHashSet<>(customers));
If you want to change the original list:
Set<Customer> depdupeCustomers = new LinkedHashSet<>(customers);
customers.clear();
customers.addAll(dedupeCustomers);
If the code in your question doesn't work, you probably have not implemented equals(Object)
on the Customer
class appropriately.
Presumably there is some key (let us call it customerId
) that uniquely identifies a customer; e.g.
class Customer {
private String customerId;
...
An appropriate definition of equals(Object)
would look like this:
public boolean equals(Object obj) {
if (obj == this) {
return true;
}
if (!(obj instanceof Customer)) {
return false;
}
Customer other = (Customer) obj;
return this.customerId.equals(other.customerId);
}
For completeness, you should also implement hashCode
so that two Customer
objects that are equal will return the same hash value. A matching hashCode
for the above definition of equals
would be:
public int hashCode() {
return customerId.hashCode();
}
It is also worth noting that this is not an efficient way to remove duplicates if the list is large. (For a list with N customers, you will need to perform N*(N-1)/2
comparisons in the worst case; i.e. when there are no duplicates.) For a more efficient solution you could use a HashSet
to do the duplicate checking. Another option would be to use a LinkedHashSet
as explained in Tom Hawtin's answer.