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Tag: hashmap

What is the purpose of placing a HashSet inside of a HashMap?

For example: private HashMap<Integer, HashSet> variableName; I understand that HashMap implements Map and doesn’t allow duplicate keys and HashSet implements Set and doesn’t allow for duplicate values, but what is the purpose of placing a HashSet inside of a HashMap? Do they not achieve similar tasks by themselves (though in different ways and with different performance)? What functionality does doing

HashMap element is removed when another HashMap name remove an element

appearList is a HashMap with fixed data. I do: Then, when I remove an element from randomPersonList, that element on appearList is also removed unexpectedly. I expect to keep appearList as original. Can anyone tell me why and how to correct my code? Answer makes randomPersonList the reference to the same object as appearList. So with both variables you are

Adding in hashmap by while loop but not working

I have the following CSV file and I would like to create a hashmap which the unique key should be the first value of each row and value should be an arraylist containing the information of each line under the first value of this row. Example CSV as below: So ideally, I would like the final ArrayList to be something

Unboxing may produce Null Pointer Exception after checking if key exists in Map

Android Studio gives the warning: Unboxing of ‘idCollisonMap.get(currentId)’ may produce ‘NullPointerException’ even though I am checking if the key exists before I perform the Map.get(). Am I actually in danger of running into a null pointer exception? My understanding is that .containsKey() check would prevent this from happening. Code snippet sample output: [{T143=1, T153=3, T141=1}] Answer Assuming nothing else is

How to Get data from nested LinkedHashMap

How to get the “test” data from this linkedHashMap response.get(“url”) = null response.get(“data.images.original.url”) = null response.get(“data”).get(“images”).get(“original”).get(“url”) toString(); result{data={images={original={url=test}}}}; Answer The “right” way would be And yes, this is ugly as all heck. Mostly because of the types you’ve chosen. By making the value of your maps Object you’ve gained flexibility on what to put in, but you put the burden

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