When creating a map, you must first decide which map implementation you will use. As mentioned initially, theHashMapimplementation is the fastest and most suitable for general use. That’s why you will use it in this tutorial. To begin, you will create a map of the world’s capitals. Ea...
Let’s see how we can use theUnmodifiableMultiValuedMapdecorator to make them immutable: @Test(expected = UnsupportedOperationException.class)publicvoidgivenUnmodifiableMultiValuedMap_whenInserting_thenThrowingException(){ MultiValuedMap<String, String> map =newArrayListValuedHashMap<>(); map.put("key1"...
Let’s consider that the source map contains duplicate values. In such cases,we can use a mapping function to apply custom rules to the input elements: public static <K, V> Map<V, K> invertMapUsingMapper(Map<K, V> sourceMap) { return sourceMap.entrySet() .stream().collect( Collectors....
In the next example, we filter a map by the keys and values. Main.java import java.util.HashMap; import java.util.Map; import java.util.stream.Collectors; void main() { Map<Integer, String> users = new HashMap<>(); users.put(1, "John Doe"); users.put(2, "Roger Roe"); ...
2.If you're only interested in the keys, you can iterate through the "keySet()" of the map: Map<String, Object> map =...;for(String key : map.keySet()) {//...} 3.If you only need the values, use "value()": for(Object value : map.values()) {//...} ...
Using Built-in Lambdas Thejava.util.functionpackage contains a set of functional interfaces which cover common use cases. To use one of these interfaces, you have to provide the implementation of its abstract method. Let’s see how this can be done for some of the most useful interfaces. ...
at java.base/java.util.Map.of(Map.java:1407) 1.2. Create Immutable Map Containing More Than 10 Key-Value Pairs When we have to add more than 10 key-value pairs in the immutableMap, we can rely onMap.ofEntries()factory method. TheofEntries()method accepts avarargsof typeEntryso we can...
Java HashMaplast modified February 21, 2024 In this article we show how to use Java HashMap collection. HashMap is a container that stores key-value pairs. Each key is associated with one value. Keys in a HashMap must be unique. HashMap is called an associative array or a dictionary ...
Here, we use thekeySet()method to get keys by creating an array list from a set returned by a map. Check out the following example, which converts a map into a list. Example 1: packagemaptolist;importjava.util.HashMap;importjava.util.List;importjava.util.Map;importjava.util.stream.Col...
Java Collection How to - Java Map Example Convert Next » « Previous