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Summary
To review the containers provided in the standard Java library:
- An array associates numerical indices to objects. It holds objects of a
known type so that you don’t have to cast the result when you’re
looking up an object. It can be multidimensional, and it can hold primitives.
However, its size cannot be changed once you create it.
- A Collection holds single elements, and a Map holds associated
pairs.
- Like an array, a List also associates numerical indices to
objects—you can think of arrays and Lists as ordered containers.
The List automatically resizes itself as you add more elements. But a
List can hold only Object references, so it won’t hold
primitives, and you must always cast the result when you pull an Object
reference out of a container.
- Use an ArrayList if you’re doing a lot of random accesses, but
a LinkedList if you will be doing a lot of insertions and removals in the
middle of the list.
- The behavior of queues, deques, and stacks is provided via the
LinkedList.
- A Map is a way to associate not numbers, but objects with
other objects. The design of a HashMap is focused on rapid access,
whereas a TreeMap keeps its keys in sorted order, and thus is not as fast
as a HashMap. A LinkedHashMap keeps its elements in insertion
order, but may also reorder them with its LRU algorithm.
- A Set only accepts one of each type of object. HashSets
provide maximally fast lookups, whereas TreeSets keep the elements in
sorted order. LinkedHashSets keep elements in insertion order.
There’s no need to use the legacy classes Vector,
Hashtable, and Stack in new code.
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