What are Different ways to Iterate Over HashMap in Java ?

There are many ways to iterate Map interface classes (HashMap, HashTable, LinkedHashMap and TreeMap) ,here with will traverse map with the help of for-each loop , Iterator interface and Lambda Expression. 

We can iterate only keys of map using keySet() method, we can iterate only values of map using values() method, and if we want to iterate keys and values of map simultaneously then we can use entrySet() method. See below example for detail.

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import java.util.HashMap; import java.util.Iterator; import java.util.Map.Entry; public class WaysToIterateHashMap { public static void main(String[] args) { HashMap<String, String> map = new HashMap<>(); map.put("UP", "UTTA PPRADESH"); map.put("GA", "GOA"); map.put("CH", "CHANDIGARH"); map.put("DL", "DELHI"); map.put("WB", "WEST BENGAL"); System.out.println("Using For-Each with keySet() :-"); for(String s : map.keySet()){ System.out.println(s+" = "+map.get(s)); } System.out.println("\nUsing ForEach with entrySet() :-"); for(Entry<String, String> en : map.entrySet()){ System.out.println(en.getKey()+" = "+en.getValue()); } System.out.println("\nUsing Iterator with keySet() :-"); Iterator<String> it = map.keySet().iterator(); while(it.hasNext()){ String key = it.next(); System.out.println(key+" = "+map.get(key)); } System.out.println("\nUsing Iterator with entrySet() :-"); Iterator<Entry<String, String>> it1 = map.entrySet().iterator(); while(it1.hasNext()){ Entry<String, String> en = it1.next(); System.out.println(en.getKey()+" = "+en.getValue()); } System.out.println("\nUsing Lambda Expression :-"); map.forEach((k,v) -> System.out.println(k+" = "+v)); } }

Output:

Using For-Each with keySet() :-

CH = CHANDIGARH

DL = DELHI

GA = GOA

UP = UTTA PPRADESH

WB = WEST BENGAL

Using ForEach with entrySet() :-

CH = CHANDIGARH

DL = DELHI

GA = GOA

UP = UTTA PPRADESH

WB = WEST BENGAL

Using Iterator with keySet() :-

CH = CHANDIGARH

DL = DELHI

GA = GOA

UP = UTTA PPRADESH

WB = WEST BENGAL

Using Iterator with entrySet() :-

CH = CHANDIGARH

DL = DELHI

GA = GOA

UP = UTTA PPRADESH

WB = WEST BENGAL

Using Lambda Expression :-

CH = CHANDIGARH

DL = DELHI

GA = GOA

UP = UTTA PPRADESH

WB = WEST BENGAL

      

Blog Author - Pushkar Khosla,
Software Developer by Profession with 3.0 Yrs of Experience , through this blog i'am sharing my industrial Java Knowledge to entire world. For any question or query any one can comment below or mail me at pushkar.itsitm52@gmail.com.

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