This article shows a few ways to update or increase a value of a key in a HashMap. Table of contents 1. Update the value of a key in HashMap 2. Increase the value of a key in HashMap 3. Java 8 getOrDefault() 4. Java 8 compute and merge 4.1 Java 8 merge example 4.2 […]
This article shows a few ways to get keys from value in HashMap. 1. HashMap can contain null for key and value 2. Get all keys from HashMap – keySet() 3. Get keys from value in HashMap 4. Get keys from value in HashMap (Java 8 Stream) 5. HashMap only has one item 6. References […]
In Java, we can use LinkedHashMap to keep the insertion order. P.S HashMap does not guarantee insertion order. 1. HashMap Generate a HashMap, UUID as key, index 0, 1, 2, 3, 4… as value. JavaHashMap.java package com.mkyong.samples; import java.util.HashMap; import java.util.Map; import java.util.UUID; import java.util.stream.IntStream; public class JavaHashMap { public static void main(String[] args) { […]
In Java, there are 3 ways to loop or iterate a HashMap 1. If possible, always uses the Java 8 forEach. Map<String, String> map = new HashMap<>(); map.forEach((key, value) -> System.out.println("[Key] : " + key + " [Value] : " + value)); 2. Normal for loop in entrySet() Map<String, String> map = new HashMap<>(); for […]
HashMap is an object that stores both key=value as a pair. This HashMap permits null values and the null key, unsynchronized and no guarantees to the order of the map. ["key","value"] = ["java","mkyong.com"] 1. HashMap Basic 1.1 Add an Item Map map = new HashMap<String, String>(); map.put("PostgreSQL", "Free Open Source Enterprise Database"); 1.2 Get an […]
