如何正确结合Hashmap <String, ArrayList<Object> &gt;和HashMap <String, Object>

Question

I want to make my code clean add have the following trouble. I want add

HashMap<String,Object> currentItem;

to my storage

HashMap<String, ArrayList<Object>> storage;

by the following way:

Add all Object of currentItem to ArrayList<Object> of storage according to the keys (they all are the same).

This is my variant how to add currentItem to storage according to the keys

if (storage.containsKey("article_link")) 
{Object tmpObj;
    ArayList<Object> listTemp;
            tmpObj = currentItem.get("article_link");
        listTemp = storage.get("article_link");
        listTemp.add(tmpObj);
        storage.put("article_link", listTemp);

        tmpObj = o.get("image");
        listTemp = storage.get("image");
        listTemp.add(tmp);
        storage.put("image", rrr);
}

and this for each hashmap key. I can write special function for repeating code, but I hope it can be solved more easier.

Thanks.

Answer 1

One thing to note here is that, you don't need to put the mapping for new arraylist again, once you modify it. The changes will be reflected in the Map automatically, since, what you are having is the reference to the actual ArrayList object.

Secondly, you don't need to do all that hard-coding . You can simply iterate over your currentItem map, and for each key-value pair, check the existence of key in storage , and if found, just update the corresponding List .

Here's how you do that: -

for (Entry<String, Object> entry: currentItem.entrySet()) {
    if (storage.containsKey(entry.getKey()) {
        storage.get(entry.getKey()).add(entry.getValue());

    } else {
        List<Object> newEntry = new ArrayList<Object>();
        newEntry.add(entry.getValue());
        storage.put(entry.getKey(), newEntry);
    }
}

Answer 2

for (Entry<String, Object> entry: currentItem.entrySet()) {
    if (!storage.containsKey(entry.getKey()) {
        storage.put(new ArrayList<Object>());
    }
    storage.get(entry.getKey()).put(entry.getValue());
}

Answer 3

Set<Entry<String,Object> entries = currentItem.entrySet();
Iterator<Entry<String,Object>> i = entries.iterator();
while(i.hasNext()) {
    Entry<String,Object> e = i.next();
    if(storage.containsKey(e.getKey()) { 
        storage.get(e.getKey()).add(e.getValue());
    }
    else {
        ArrayList l = new ArrayList();
        l.add(e.getValue());
        storage.put(e.getKey(),l);
    }
}