Java Collections Tutorial 02 | List - ArrayList in Java | Java9s.com
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List is an ordered collection. It arranges its elements in a sequence with an index. A list is very similar to an Array except that an Array cannot expand in size but a list can expand when and then we try to insert a new element.
ArrayList is the concrete implementation of the Collection and List interfaces.
ArrayList is the most frequently used Collection. So, if you notice the methods with an index in the method signature, then they are added by the List interface and most of the other methods you see are from the Collection interface.
Please remember that most of these methods are common in other collection types like Set and Queue.