Put arraylist of hashmap into another

Question

I want to put an ArrayList<HashMap<String, Object>> into another ArrayList<HashMap<String, Object>>. How can I do that?

I was trying with the assignment operator (=) but I found out that it just points to the reference, I want to put the elements into another.

So you want to copy everything, including he objects within the HashMap, correct? — arshajii
– arshajii, Commented Jun 21, 2012 at 20:11

cklab · Accepted Answer · 2012-06-21 20:13:49Z

4

You can use the addAll method, but bear in mind that'll not duplicate the HashMaps and much less the Objects within!

edited Jun 21, 2012 at 20:13

cklab

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answered Jun 21, 2012 at 20:10

Miquel

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Jason · Accepted Answer · 2012-06-21 20:10:44Z

1

Try this:

List<HashMap<String, Object>> newList = new ArrayList<HashMap<String,Object>>();
for (HashMap<String, Object> hm: oldList) {
    newList.add(hm);
}

answered Jun 21, 2012 at 20:10

Jason

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2 Comments

Jason Over a year ago

I didn't make any point about addAll. My method is pretty quick and dirty, but for a real eye-opener, look at the source of addAll() in ArrayList.java.

Miquel Over a year ago

He he, sorry, you did not make a point indeed. I guess I was making it, that addAll would be more compact and do the same

chaosguru · Accepted Answer · 2012-06-21 20:12:32Z

1

You can create a new ArrayList Object and just call the addAll method and pass the ArrayList you want to copy

Another way is Collections.copy(desc,src) but this is not feasible since the size of both the List must be equal.

answered Jun 21, 2012 at 20:12

chaosguru

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