Java : Get Data from Nested HashMap

Question

Hi Folks i have looked at below mention question for answer but it was not helpful as they give answer for static value while i need to get value from dynamic approch

How to put/get values into/from Nested HashMap

Getting value from Nested HashMap into another Map

How do I access nested HashMaps in Java?

This is my Scenario :

This is my class for adding and retrieving data from HashMap :-

HashMap<Integer, String> xmlQueryNode = new HashMap<Integer, String>();
HashMap<Integer, HashMap<Integer, String>> splunkHashMap = new HashMap<Integer, HashMap<Integer, String>>();
id = 0;
xmlQueryNode.put(0, "F0name");
xmlQueryNode.put(1, "L0name");
xmlQueryNode.put(2, "M0name");

splunkHashMap.put(id, xmlQueryNode);

id = 1;
xmlQueryNode.put(0, "F1name");
xmlQueryNode.put(1, "L1name");
xmlQueryNode.put(2, "M1name");

splunkHashMap.put(id, xmlQueryNode);

id = 2;
xmlQueryNode.put(0, "F2name");
xmlQueryNode.put(1, "L2name");
xmlQueryNode.put(2, "M2name");

splunkHashMap.put(id, xmlQueryNode);

id = 3;
xmlQueryNode.put(0, "F3name");
xmlQueryNode.put(1, "L3name");
xmlQueryNode.put(2, "M3name");

splunkHashMap.put(id, xmlQueryNode);

for (Integer key : splunkHashMap.keySet()) {
    HashMap<Integer, String> temp =  new HashMap<Integer, String>();
    //System.out.println(key);
    temp = otsdbQueryData.get(key);
    for(Integer key1: temp.keySet()){
        System.out.println(temp.get(key1));
    }
}

Problem with this code is that i get below output for all 4 entries :-

F3name
L3name
M3name

F3name
L3name
M3name

F3name
L3name
M3name

F3name
L3name
M3name

Can anyone point me where i am making mistake because My hashmaps are being overwritten by last inserted hashmap??

Siva Kumar · Accepted Answer · 2015-09-28T10:34:44.077

after put inner hashmap you need to reinitialise that map.

xmlQueryNode = new HashMap<Integer,String>();
xmlQueryNode.put(0, "F1name");
xmlQueryNode.put(1, "L1name");
xmlQueryNode.put(2, "M1name");

otherwise it will update the same reference.

Please check the updated code.

int id =0;

HashMap<Integer, String> xmlQueryNode = new HashMap<Integer, String>();
HashMap<Integer, HashMap<Integer, String>> splunkHashMap = new HashMap<Integer, HashMap<Integer, String>>();
id = 0;
xmlQueryNode.put(0, "F0name");
xmlQueryNode.put(1, "L0name");
xmlQueryNode.put(2, "M0name");

splunkHashMap.put(id, xmlQueryNode);

xmlQueryNode = new HashMap<Integer, String>();
id = 1;
xmlQueryNode.put(0, "F1name");
xmlQueryNode.put(1, "L1name");
xmlQueryNode.put(2, "M1name");

splunkHashMap.put(id, xmlQueryNode);

xmlQueryNode = new HashMap<Integer, String>();
id = 2;
xmlQueryNode.put(0, "F2name");
xmlQueryNode.put(1, "L2name");
xmlQueryNode.put(2, "M2name");

splunkHashMap.put(id, xmlQueryNode);

xmlQueryNode = new HashMap<Integer, String>();
id = 3;
xmlQueryNode.put(0, "F3name");
xmlQueryNode.put(1, "L3name");
xmlQueryNode.put(2, "M3name");

splunkHashMap.put(id, xmlQueryNode);

for (Integer key : splunkHashMap.keySet()) {
    HashMap<Integer, String> temp =  new HashMap<Integer, String>();
    //System.out.println(key);
    temp = splunkHashMap.get(key);
    for(Integer key1: temp.keySet()){
        System.out.println(temp.get(key1));
    }
}

I dont understand what you are trying to say. Where exactly i need to reinitialiset that map? — mihir6692, Sep 28 '15 at 10:31
Yo Man you are awesome... Do you know reason for doing this? you can also point to me to any link for explanation. — mihir6692, Sep 28 '15 at 10:37
@mihir6692.. You just maintained the same reference and update it. First you add three value in hashmap and updated to outer map. again you adding the same inner map so it will update in old map also. Because java is call by reference. — Siva Kumar, Sep 28 '15 at 10:38

score 0 · Answer 2 · answered Sep 28 '15 at 10:34

xmlQueryNode reference is getting overwritten again and again. Check below code.

HashMap<Integer, String> xmlQueryNode = new HashMap<Integer, String>();
HashMap<Integer, HashMap<Integer, String>> splunkHashMap = new HashMap<Integer, HashMap<Integer, String>>();
id = 0;
xmlQueryNode.put(0, "F0name");
xmlQueryNode.put(1, "L0name");
xmlQueryNode.put(2, "M0name");

splunkHashMap.put(id, xmlQueryNode);

id = 1;
xmlQueryNode = new HashMap<Integer,String>();
xmlQueryNode.put(0, "F1name");
xmlQueryNode.put(1, "L1name");
xmlQueryNode.put(2, "M1name");

splunkHashMap.put(id, xmlQueryNode);

id = 2;
xmlQueryNode = new HashMap<Integer,String>();
xmlQueryNode.put(0, "F2name");
xmlQueryNode.put(1, "L2name");
xmlQueryNode.put(2, "M2name");

splunkHashMap.put(id, xmlQueryNode);

id = 3;
xmlQueryNode = new HashMap<Integer,String>();
xmlQueryNode.put(0, "F3name");
xmlQueryNode.put(1, "L3name");
xmlQueryNode.put(2, "M3name");

splunkHashMap.put(id, xmlQueryNode);

for (Integer key : splunkHashMap.keySet()) {
    HashMap<Integer, String> temp =  new HashMap<Integer, String>();
    //System.out.println(key);
    temp = otsdbQueryData.get(key);
    for(Integer key1: temp.keySet()){
        System.out.println(temp.get(key1));
    }
}

Java : Get Data from Nested HashMap

2 Answers2