Inner Hashmap value is over ridden by new value

Question

In Java, I want my hash map to have a structure like this

{12/10/2015 = {8977867 = 4 }}
{13/10/2015 = {8977867 = 3 }}

Presently my hash map is like

{12/10/2015 = {8977867 = 3 }}
{13/10/2015 = {8977867 = 3 }}

Map<String, Object>trial=new HashMap<String,Object>();
HashMap<Date, Map<String, Object>> map1 = new HashMap<>();
String cuurentDate;

for(event = some condition) {
    String key = event.getKey;
    Integer value= event.getValue;
    trial.put(key,value)
}
map1.put(currentDate,trial)

The above is the code. I will be iterating through date values.

The inner map value is updated to a new value, or it's overridden. But for every date I want inner map to hold the actual date values.

Would I have to delete the inner-map once I iterate through each day or is there any other way to do it?

Answer 1

The problem is likely in the code you didn't include. Each time you put an inner HashMap instance in your map1 Map, you should create a new HashMap and not reuse the previous one.

HashMap<Date, Map<String, Object>> map1 = new HashMap<>();    

Map<String, Object> trial=new HashMap<String,Object>();
String currentDate = ...;
for(...){
    ...
    trial.put(key,value);
}
map1.put(currentDate,trial);

trial=new HashMap<String,Object>(); // the important thing you are probably missing
currentDate = ...;
for(...){
    ...
    trial.put(key,value);
}
map1.put(currentDate,trial);

Answer 2

You have to define trial inside the for loop, and after changing the value of trial , immediately put it to map1 .

HashMap<Date, Map<String, Object>> map1 = new HashMap<>();
String cuurentDate;
for(event = some condition){
    Map<String, Object>trial=new HashMap<String,Object>();
    String key = event.getKey;
    Integer value= event.getValue;
    trial.put(key,value)
    map1.put(currentDate,trial)
}