Map<K, V> class abstract interface

A collection of key/value pairs, from which you retrieve a value using its associated key.

There is a finite number of keys in the map, and each key has exactly one value associated with it.

Maps, and their keys and values, can be iterated. The order of iteration is defined by the individual type of map. Examples:

• The plain HashMap is unordered (no order is guaranteed),
• the LinkedHashMap iterates in key insertion order,
• and a sorted map like SplayTreeMap iterates the keys in sorted order.

It is generally not allowed to modify the map (add or remove keys) while an operation is being performed on the map, for example in functions called during a forEach call. Modifying the map while iterating the keys or values may also break the iteration.

It is generally not allowed to modify the equality of keys (and thus not their hashcode) while they are in the map. Some specialized subtypes may be more permissive, in which case they should document this behavior.

Key equality must be an equality relation. If the key stored in a map and the key used for lookup do not agree on whether the two are equal, so equality is not symmetric, then lookup behavior is unspecified.