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How to Remove Duplicates from ArrayList in Java

ArrayList is the most popular implementation of List interface from Java's Collection framework, but it allows duplicates. Though there is another collection called Set which is primarily designed to store unique elements, there are situations when you receive a List e.g. ArrayList in your code and you need to ensure that it doesn't contain any duplicate before processing. Since with ArrayList you cannot guarantee uniqueness, there is no other choice but to remove repeated elements from ArrayList. There are multiple ways to do this, you can follow the approach we used for removing duplicates from array in Java, where we loop through array and inserting each element in a Set, which ensures that we discard duplicate because Set doesn't allow them to insert, or you can also use remove method of ArrayList to get rid of them, once you found that those are duplicates.