Map
Map is a data structure that allows you to store key-value pairs.
* Each key refers to a value, like in a dictionary.
* word --> definition
We get a value from the map by providing the key.
We put a value into the map with its key.
Map and Collection¶
Map is part of the Java Collections Framework, but it is not a subinterface of Collection.
Keys and Values¶
- The key must be unique.
- A key can map to only a single value.
- Multiple keys can map to a single value.
Map<K, V>¶
As with Set and List, we tell a Map what the types of its keys and values will be.
Map<Integer, String> map; // A Map of Integer keys and String values
Map<Integer, Album> albums; // A Map of Integer keys and Album values
Map Methods¶
V put(key, value) - adds a key-value pair to the Map, and returns the old value associated with this key (or null if there was no mapping).
V get(key) - returns the value associated with the given key (or null if this map contains no mapping for the key).
boolean containsKey(key) - returns true if the key is in the Map.
boolean containsValue(value) - returns true if the value is in the Map.