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 BiConsumerMap.
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 lambdaforEach method. Then, we created a BiConsumerforEach 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.Set;
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<Integer> keys = numbers.keySet();
for (Integer key: keys){
System.out.println(key + " # " + numbers.get(key));
}
}
}In the code above, we used the keySet method of the HashMap to get all the keys of the HashMap, and looped all the keys to print values of all of them.
3. entrySet() method
The entrySet method returns a Set with key-value mappings as an Entry.
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);
}
}
}In the code above, we used the entrySet() method to get a Set which contains all the mapping of the HashMap. Then, we looped the entrySet and printed the key and value.
RELATED TAGS
CONTRIBUTOR
View all Courses
