Java HashMap - Cheat sheet

import java.util.HashMap; import java.util.LinkedHashMap; public class MapDemo { public static void main(String[] args) { //Initializing a new hashmap HashMap<Integer, String> intToStringMap = new HashMap<>(); LinkedHashMap<String, String> map = new LinkedHashMap<>(); //Adding a new entry System.out.println("====== Adding a new entry ======"); intToStringMap.put(1, "One"); intToStringMap.put(2, "Two"); System.out.println(intToStringMap); //Getting a value by key System.out.println("====== Getting a value by key ======"); System.out.println(intToStringMap.get(2)); System.out.println(intToStringMap.get(3)); //Getting default value System.out.println("====== Getting default value ======"); System.out.println(intToStringMap.getOrDefault(3, "NA")); //Checking key in the map System.out.println("====== Checking key in the map ======"); System.out.println(intToStringMap.containsKey(3) + ", " + intToStringMap.containsKey(2)); //Checking value System.out.println("====== Checking value ======"); System.out.println(intToStringMap.containsValue("One")); //Clearing hashmap System.out.println("====== Clearing hashmap ======"); //intToStringMap.clear(); //Checking size of hashmap + isEmpty System.out.println("====== Checking size of hashmap + isEmpty ======"); System.out.println(intToStringMap.size() + ", " + intToStringMap.isEmpty()); //compute System.out.println("====== compute ======"); intToStringMap.compute(9, (integer, s) -> integer + "-" + s); System.out.println(intToStringMap); //computeIfAbsent System.out.println("====== computeIfAbsent ======"); intToStringMap.computeIfAbsent(7, integer -> { return String.valueOf(integer); }); System.out.println(intToStringMap); //computeIfPresent System.out.println("====== computeIfPresent ======"); //Getting all entries System.out.println("====== Getting all entries ======"); intToStringMap.entrySet().forEach(integerStringEntry -> System.out.println(integerStringEntry.getKey() + "==>" + integerStringEntry.getValue())); //Getting all keys System.out.println("====== Getting all keys ======"); for(Integer key : intToStringMap.keySet()) { System.out.println(key); } //Getting all Values System.out.println("====== Getting all Values ======"); intToStringMap.values().forEach(System.out::println); //forEach System.out.println("====== forEach ======"); //merge System.out.println("====== merge ======"); System.out.println(intToStringMap); intToStringMap.merge(2, "TWO", (s, s2) -> s.concat("-").concat(s2)); System.out.println(intToStringMap); //putAll System.out.println("====== putAll ======"); HashMap<Integer, String> target = new HashMap<>(); target.put(5, "Five"); target.put(6, "Six"); intToStringMap.putAll(target); System.out.println(intToStringMap); //putIfAbsent System.out.println("====== putIfAbsent ======"); intToStringMap.putIfAbsent(3, "Three"); intToStringMap.putIfAbsent(2, "sdjfgjsdgf"); System.out.println(intToStringMap); //remove System.out.println("====== remove ======"); intToStringMap.put(3, "Three"); intToStringMap.put(4, "Four"); intToStringMap.put(4, "FOUR"); System.out.println(intToStringMap); intToStringMap.remove(4); System.out.println(intToStringMap); intToStringMap.remove(3, "Three"); System.out.println(intToStringMap); //replace, replaceAll System.out.println("====== replace, replaceAll ======"); intToStringMap.replace(2, "TWO"); System.out.println(intToStringMap); intToStringMap.replace(2, "TWO" , "Two"); System.out.println(intToStringMap); intToStringMap.replaceAll((key, value) -> key % 2 == 0 ? value.concat("-Even") : value); System.out.println(intToStringMap); } }