How to Convert HashMap to List

By Dhiraj Ray, 19 October,2016   597

HashMap is a class in Java that implements Map interface.It is an unsorted and unordered map whereas ArrayList implements List interface and maintains insertion order.Here we will try to convert a HashMap into an ArrayList.

Let us define a HashMap first.

Map<String, String> map = new HashMap<String, String>();

At first,let us see how to get list of keys from a HashMap.There is an implicit method defined in java library to get the list of keys of a HashMap.And after getting the list of keys, construct an ArrayList with it.

Set<String> keys = map.keySet(); //list of all the keys defined in Hashmap ArrayList<String> listOfKeys = new ArrayList<String>(keys);

Similarly, extract the values of a HashMap and construct an ArrayList out of it as below:

Collection<String> values = map.values(); //list of all the values defined in Hashmap ArrayList<String< listOfValues = new ArrayList<String>(values);

Now let us constuct a single ArrayList having both the keys and values of a HashMap in a single shot.

Set<Entry<String, String>> entrySet = map.entrySet(); ArrayList<Entry<String, String>> listOfEntries = new ArrayList<Entry<String, String>>(entrySet); for (Entry<String, String> entry : listOfEntries) { System.out.println(entry.getKey() + " : " + entry.getValue()); }


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