adding a key to HashMap without the value?

Question

Is there a way to add a key to a HashMap without also adding a value? I know it seems strange, but I have a HashMap> amd I wan

Answer 1

//This program should answer your questions
import java.util.*;
public class attemptAddingtoHashMap { //Start of program

//MAIN METHOD #################################################

public static void main(String args[]) {  //main begins

Map> hmTrial = new HashMap>(); 

ArrayList alTrial = new ArrayList();//No values now

if (hmTrial.containsKey("first")) {
hmTrial.put("first", alTrial); }

else {hmTrial.put("first",alTrial);}
//in either case, alTrial, an ArrayList was mapped to the string "first"
//if you choose to, you can also add objects to alTrial later
System.out.println("hmTrial is " + hmTrial); //empty now
alTrial.add("h");
alTrial.add("e");
alTrial.add("l");
alTrial.add("l");
alTrial.add("o");
System.out.println("hmTrial is " + hmTrial);//populated now

   } //end of main
//#############################################################################################################

} //end of class

//Note - removing objects from alTrial will remove the from the hashmap
//You can copy, paste and run this code on https://ide.geeksforgeeks.org/