{"id":32236,"date":"2023-01-27T14:33:43","date_gmt":"2023-01-27T09:03:43","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-java-unable-to-access-a-hashmap-within-a-hashmap\/"},"modified":"2023-01-27T14:33:43","modified_gmt":"2023-01-27T09:03:43","slug":"solved-java-unable-to-access-a-hashmap-within-a-hashmap","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-java-unable-to-access-a-hashmap-within-a-hashmap\/","title":{"rendered":"[Solved] Java – Unable to access a HashMap within a HashMap"},"content":{"rendered":"

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I’m not sure that I really understand your description of what you are doing, but this stands out:<\/p>\n

    this.containers.put(this.currentHashMapKey, tempHashMap);\n    \/\/ ...\n    tempHashMap.clear();\n<\/code><\/pre>\n
When you call clear()<\/code>, you remove all entries from tempHashMap<\/code>.  Since this is the map object that you added as a value in the containers<\/code> map, you are clearing it there as well<\/em>.<\/p>\n
One possible solution is to create a new tempHashMap<\/code> on every iteration … and don’t call clear()<\/code> after adding it to containers<\/code>.<\/p>\n
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Explanation:<\/p>\n
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I thought it created a copy of the HashMap when you added it. <\/p>\n<\/blockquote>\n
You appear to think that<\/p>\n
    this.containers.put(this.currentHashMapKey, tempHashMap);\n<\/code><\/pre>\n
will create a copy of tempHashMap<\/code>. <\/p>\n
This is NOT so.  <\/p>\n
In fact, what you are doing is storing the reference<\/em> to your “temporary hash map” as the entry value in the container<\/code> map.   Indeed, if you then reuse the temporary map, you will end up will many references to that one map object in your containers<\/code> map.<\/p>\n
A Map::put(key, value)<\/code> operation does not copy \/ clone \/ whatever the key<\/code> object or the value<\/code> object.  It just stores the references in the map entry.  If you then mutate those objects:<\/p>\n