How to get the number of entries in a HashMap, including the duplicate entries?

[Varuna Seneviratna]

  import java.util.HashMap;
/**
 * Write a description of class PhoneBook here.
 * 
 * @author (Varuna Seneviratna) 
 * @version (0.01)
 */
public class PhoneBook
{
    // instance variables - replace the example below with your own
    private HashMap phoneBook;
 
    /**
     * Constructor for objects of class PhoneBook
     */
    public PhoneBook()
    {
        // initialise instance variables
        phoneBook=new HashMap();
        phoneBook.put("Varuna Seneviratna", "011-2888620");
        phoneBook.put("Lisa Jones", "(402) 4536 4676");
        phoneBook.put("William H. Smith", "(998) 5488 0121");
         phoneBook.put("Lisa Jones", "(402) 4536 4676");
    }
 
    /**
     * An example of a method - replace this comment with your own
     * 
     * @param  y   a sample parameter for a method
     * @return     the sum of x and y 
     */
    public void printTeleNumber(String name)
    {
        if(phoneBook.containsKey(name)){
            String teleNumber=(String) phoneBook.get(name);
            System.out.println("The Telephone Number of " +
                           name + " is: " + teleNumber);
        }else{
            System.out.println("The is not present in the list!");   
        }
        
    }
    public void inputEntry(String name, String number)
    {
        phoneBook.put(name, number);
        
    }
    public void numberOfEntries()
    {
        System.out.println("The number of entries: " + phoneBook.size());
        
    }
}
 

In the above class I have added a duplicate entry

(phoneBook.put("Lisa Jones", "(402) 4536 4676") :wink: , 

including that there should be four entries, But the size() returns 3, Is there a way to get the total number of entries including the duplicate entries

Varuna

[Henry Wong]

including that there should be four entries, But the size() returns 3, Is there a way to get the total number of entries including the duplicate entries

Unfortunately, hashmaps don't support duplicates. The reason it is reporting three entries is because there is only three entries in the map.

Henry

[Mark Vedder]

If it helps any, keep in mind that the HashMap's put method will return the previous value associated with the key (returning null if there was no value for the key or if the value for the key was null). In some situation this can be useful.

For something like a phone book where a key (a person's name) is very likely to have duplicate entries, I would use a double collection. Make your PhoneBook Map use the name for the key and another collection as the value. That collection would hold the phone numbers for that person. You could simply use a set which would prevent multiples of the same phone number; or use another Map with the key being the phone number type, "work", "home", "cell", etc. So you would end up with one master collection which holds a number of other collections.

I hope that helps.