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How to freeze a HashMap to avoid other changes?
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How to freeze a HashMap to avoid other changes?
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The question is pretty much self-explanatory. I have a data structure (I mentioned a HashMap but it could be a Set or a List also) which I initially populate:
Map<String, String> map = new HashMap<String, String>();
for( something ) {
map.put( something );
}
After the structure has been populated, I never want to add or delete any items:
map.freeze();
How could one achieve this using standard Java libraries?
The best you can do with standard JDK libraries is Collections.unmodifiableMap().
Note that you must drop the original map reference, because that reference can still be accessed and changed normally. If you passed the old reference to any other objects, they still will be able to change your map.
Best practice:
map = Collections.unmodifiableMap(map);
and make sure you didn't share the original map reference.
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