How to Efficiently Remove Duplicates From a List in Java?

Efficiently Removing Duplicates from a List

When working with lists, it's often necessary to remove duplicate elements to streamline data processing. However, the following code snippet may encounter issues:

List<Customer> listCustomer = new ArrayList<>();    
for (Customer customer: tmpListCustomer)
{
  if (!listCustomer.contains(customer)) 
  {
    listCustomer.add(customer);
  }
}

What's the Limitation?

This approach relies on the contains() method to check for duplicates. However, it only works correctly if the Customer class overrides the equals() and hashCode() methods to compare objects effectively. If these methods are not implemented or implemented incorrectly, duplicates may not be detected, leading to inaccuracies.

Efficient Removal Techniques

To effectively remove duplicates, there are two methods to consider:

1. Preserve Order:

If maintaining the existing order of elements is critical, use a LinkedHashSet. This set retains insertion order, allowing you to convert it back to a list while preserving the sequence.

List<Customer> depdupeCustomers =
    new ArrayList<>(new LinkedHashSet<>(customers));

2. Modify Original List:

If modifying the original list is acceptable, utilize a Set to store unique elements and update the original list accordingly.

Set<Customer> depdupeCustomers = new LinkedHashSet<>(customers);
customers.clear();
customers.addAll(dedupeCustomers);

Both methods offer efficient solutions for removing duplicates from a list, ensuring data integrity and optimizing performance.

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