Java中具有hashmap实现的电话簿

Question

I have to make an app that would simulate a phone book in java, using hash map(s). I want to implement 2 methods for search(enter a name to get a number and enter a number to get a name).

Is there any way to make both methods work with only 1 hash map defined like this HashMap<Person, Number> pb = new HashMap<>(); (where Person and Number are classes)?

Answer 1

No you need 2 Maps in this case Map<Person, Number> and Map<Number, Person> if you want to have a fast access to your data with only one map you would need to iterate over the values which is of course much slower.

You can also use a BiMap from Google guava to do both with one map

A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as that of its keys. This constraint enables bimaps to support an "inverse view", which is another bimap containing the same entries as this bimap but with reversed keys and values

Answer 2

This can be done via a BidiMap (Bidirectional map) available with apache commons collection. See https://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/BidiMap.html for more details. But, in this case, names and numbers has to be unique. If it is not possible, then you will either have to maintain two maps or use one map and iterate the values.