How to Convert HashMap to List

author-imageBy Dhiraj, 19 October,2016   1K

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);

 Other Interesting Posts
Hello World Java Program Breakup
Serialization and Deserialization in Java with Example
Random password Generator in Java
Convert HashMap to List in Java
Sorting HashMap by Key and Value in Java
Spring Boot Security Redirect after Login with complete JavaConfig
Websocket spring Boot Integration with complete JavaConfig
Spring MVC Angularjs Integration with complete JavaConfig
Spring Hibernate Integration with complete JavaConfig

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());
}

Conclusion

I hope this article served you that you were looking for. If you have anything that you want to add or share then please share it below in the comment section.

Further Reading on Core Java

1. Sorting Hashmap By Key And Value

2. Why Wait Notify Notifyall Defined In Object Class

3. Comparable And Comparator In Java With Example

4. Random Password Generator Java

5. Serialization And Deserialization Java Example

If You Appreciate What We Do Here On Devglan, You Should Consider: