The java.util.Map interface represents a mapping between keys and their values. A map cannot contain duplicate keys; and each key can map to at most one value.
Map is an interface, then you need to instantiate a concrete implementation of that interface in order to use it; there are several
Map implementations, and mostly used are the
A map is an object which store keys with an associated value for each key. A key and its value are sometimes called a key/value pair or an entry. Maps typically provide these features:
The most commonly used map implementation is HashMap. It works well with keys that are strings or numbers.
Plain maps such as HashMap are unordered. Iterating through key/value pairs may return individual entries in any order. If you need to iterate through map entries in a controlled fashion, you should look at the following:
Sorted maps such as TreeMap will iterate through keys in their natural order (or in an order that you can specify, by providing a Comparator). For example, a sorted map using numbers as keys would be expected to iterate through its entries in numeric order.
LinkedHashMap permits iterating through entries in the same order that they were inserted into the map, or by the order of most recently accessed.