You can watch this video where I explain these operations https://youtu.be/vtjkyOaHSyw
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);
}
}
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