Java Collections Framework Flashcards
6 cards from real SCJP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Java Collections Framework flashcards as text
Which Java collection class allows duplicate elements and maintains insertion order?
Answer: ArrayList
`ArrayList` is an ordered, index-based list that allows duplicate elements and preserves insertion order.
Which interface does HashMap implement?
Answer: Map
`HashMap` implements the `Map` interface, storing key-value pairs where keys must be unique.
What is the time complexity of retrieving an element from a HashMap by key (average case)?
Answer: O(1)
HashMap provides O(1) average-case performance for `get()` and `put()` due to hashing.
Which collection maintains elements in a sorted natural order and does not allow duplicates?
Answer: TreeSet
`TreeSet` is a sorted Set implementation that stores unique elements in their natural order or by a Comparator.
What happens when you add a duplicate key to a HashMap?
Answer: The old value is replaced by the new value
When a duplicate key is inserted into a HashMap, the existing value associated with that key is overwritten.
Which of the following is NOT part of the Java Collections Framework hierarchy?
Answer: Array
Arrays are native Java constructs and are not part of the Collections Framework; they do not implement Collection or Map.
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