Converting immutable to mutable map java

Question

I have an immutable map that I get from the method in another part. And when processing I want to delete a key from it and then use it further, the key is always on the map.

    ImmutableMap<String, Object> immutableMap =  doSomethingAndGetImmutableMap();
    
    // convert to mutable
    Map<String, Object>  newMutableMap =  ??

    newMutableMap.remove("pin");
   
    // other code

Is there any built-in method to do convert immutable to mutable map java? I saw there are several ways to do the opposite but not from immutable to mutable map.

I used Maps.newHashMap but is it the best and the most efficient way?

Answer 1

You can simply create a new HashMap from the existing Map using the copy constructor.

 HashMap<String, Object> = new HashMap<>(immutableMap);

Note that this is a brand new object. There isn't a way to make an immutable map mutable. That would be breaking abstraction. I guess conceptually you could design mutable wrapper for an immutable map that stored the changes in a second (private) map structure. But Guava doesn't appear to support that.

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Is this or Maps.newHashMap more performant?

Guava Maps.newHashMap(map) simply returns new HashMap<>(map) . That call will be inlined by the JIT compile, so there should be zero performance difference on a modern JVM once the code has been JIT compiled.

You are almost certainly wasting your time micro-optimizing this kind of stuff:

• You should FIRST design and write the application code and get it to work.
• THEN you benchmark it.
• THEN you decide from the benchmark results if the application needs optimizing at all.
• THEN you profile it to determine where the performance hotspots.
• THEN you optimize the performance hotspots.

Unless there is something really weird, following the above procedure would have lead to you not wasting your time asking this question. To paraphrase ¹ Donald Knuth:

"Premature optimization is the root of all evil" .

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^{1... and oversimplify / take out of context...}