How to iterate HashMap in Java

Suppose this is the HashMap you are defining:

HashMap<K,V> h = new HashMap<>();

In, there is this decleration.

transient Set<Map.Entry<K,V>> entrySet;

This Set stored all the Entry class objects. Entry class objects are the objects which stores key-value pair in HashMap. Entry class has fields [K key,V value,Map.Entry<K,V> next] etc. This diagram will give you a idea about how java implement HashMap and store key-values:

HashMap Implementation in Java

Code to Iterate:

Set<Map.Entry<K,V>> set = h.entrySet();
#entrySet() function returns a Set which contains all the Map.Entry<K,V> objects present in HashMap.
#So you need to iterate over a Set now.
Iterator<Map.Entry<K,V>> it = set.iterator();

             Map.Entry<K,V> pair =;
             V value = pair.getValue();
             K key = pair.getKey();
             #you can use value and key according to your need

Usecase Example:

Suppose you are storing ArrayList as a Value(V) in HashMap. Now you need to sort all the ArrayList’s stored in HashMap. You can do this via iterating over HasMap and get the Object of ArrayList then you can sort it.

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