How to loop through HashMap in Java

We can loop through a HashMap in a number of different ways. In this shot, we will learn three common ways to loop a HashMap.

1. `forEach` method

The forEach method loops through all the entries of the HashMap. The forEach method takes the BiConsumerRepresents a function that accepts two input arguments and returns no result function interface as input and processes the entries of the Map.

import java.util.HashMap;
import java.util.function.BiConsumer;

class LoopHashMapByForEach {
    public static void main(String[] args) {

        // create an HashMap
        HashMap<Integer, String> numbers = new HashMap<>();

        numbers.put(1, "One");
        numbers.put(2, "Two");
        numbers.put(3, "Three");
        
        numbers.forEach( (key, value) -> {
            System.out.println(key +" - " +value);
        });

        System.out.println("---------");
        System.out.println("Using Bi Consumer");

        BiConsumer<Integer, String> biConsumer = (key, value) -> System.out.println(key + " # " + value);
        numbers.forEach(biConsumer);

    }
}

In the code above, we have created a HashMap and used the forEach method to loop the HashMap. We passed a lambdaLambda expressions are an anonymous function (function without name). We can pass the Lambda expression as a parameter to another function. We can pass the lambda expression as an argument for the method which is expecting a functional interface as an argument. function as an argument to the forEach method. Then, we created a BiConsumerRepresents a function that accepts two input arguments and returns no result function and passed it to the forEach method.

2. `keySet` of HashMap

The keySet method returns all the keys of the HashMap as a Set.

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.function.BiConsumer;

class LoopHashMapByForEach {
    public static void main(String[] args) {

        // create an HashMap
        HashMap<Integer, String> numbers = new HashMap<>();

        numbers.put(1, "One");
        numbers.put(2, "Two");
        numbers.put(3, "Three");

        Set<Map.Entry<Integer, String>> entries = numbers.entrySet();
        for (Map.Entry<Integer, String> entry : entries) {
            Integer key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + " # " + value);
        }
    }
}

How to loop through HashMap in Java

1. forEach method

2. keySet of HashMap

3. entrySet() method

1. `forEach` method

2. `keySet` of HashMap

3. `entrySet()` method