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Max Sandoval
Asked: 2020-05-12 13:07:34 +0800 CST 2020-05-12 13:07:34 +0800 CST

What is the difference between Map and HashMap in JAVA?

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I am making a View Model in which I plan to receive a JSONObject through Web Services, the issue is that I need to receive an object that is a list of data lists, I have an idea of ​​how to represent this, creating a variable.

private Map<Integer,Map<Integer,Map>> MiListaDeListas;

But while researching I came across the doubt of HashMap , I know that one is an implementation of the other, but I really couldn't understand the concept between them.

What is the difference and in what cases is it better to use one of the other.

java

1 Answers

  1. Best Answer

    Mapis an interface that defines the general behavior of a structure that maintains a relationship of key --> value.

    So HashMapit is just one implementation (although probably the most common) of one Mapof several that are possible. Other implementations of Mapare for example Hashtable, ConcurrentHashMap, WeakHashMap, etc. Each has its pros and cons depending on what you're trying to do.

    When possible, especially if your code is part of a low-level generic library, it is advantageous to define the code using the Map. This allows the same code to be used with any of its implementations according to the user's taste.

    For example, if you define the following method:

    public void HacerAlgoConCualquierTipoDeMap(Map<int,String> tabla) {
  // ...
}

    ...then the same method can be executed without problems by passing it a HashMap, Hashtable, ConcurrentHashMap, TreeMapor any of the implementations of Map.

    But if your code absolutely requires the type of to Mapbe a HashMap(perhaps for performance reasons or whatever), then it's okay to use HashMapto prevent other implementations from being used in that case.

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