Hash Map : Question about duplicate keys

[sciprog22]

Hello,

Thank you for your time!

I have a Hashmap that has keys of of type Account (custom class) and the values are strings. The Account class has the following private variables:
1) name (String type)
2) account number (String type)
3) balance (type double).

Following are the files:

public class Account implements
{
    private String name, a_number;
    private double balance;





        public Account (String name, String a_number, double balance)
            {
                this.name = name;
                this.a_number = a_number;
                this.balance = balance;
            }

            public String getName()
            {
                return name;
            }

            public String getANumber()
            {
                return a_number;
            }

            public double getBalance()
            {
                return balance;
            }

            @Override
            public boolean equals(Object a)
            {
                if (a == null)
                {
                    return false;
                }
                else
                {
                    Account temp = (Account) a;
                    if (this.name.equals(temp.name))
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
            }

            @Override
            public int hashCode()
            {
                return  name.hashCode();
            }


        }

        import java.util.HashMap;
        import java.util.HashSet;

        public class Maps
        {
            private HashMap <Account, String> map;

            public Maps()
            {
                map = new HashMap <Account, String>();
                createMap();
            }

            public void createMap()
            {

                map.put (new Account ("A", "14243", 46778), "444");
                map.put (new Account ("A", "142463", 677489), "23");
                HashSet <Account> hs = new HashSet<Account> ( map.keySet());
                for (Account s : hs)
                {
                    if (map.get(s).equals("23"))
                    {
                        System.out.println (s.getName() + "  " + s.getANumber() + "  " + s.getBalance());
                    }
                }

                Account c = new Account ("A", "14243", 46778);
                System.out.println ("Value for Account c = " + map.get(c));


            }

            public static void main( String args[] )
            {
                Maps w = new Maps();
            }

        }

My Question:

When I ran this program, I expected the output to be:

A, 142463, 677489

but, I am getting the following output:

A 14243 46778.0

My understanding was that when a duplicate key is added (as defined in the equals() method) to a hash map, it replaces the old (key,value) pair.

I then recreated the old Account object and tried to get its key value. The output was as below:

A 14243 46778.0
Value for Account c = 23

That is, its keeping the old key (A 14243 46778.0), but replacing its previous value (444) with the value of the newly added Account (23).

Also, when I check for "444" in the map, I am no longer able to obtain the corresponding key as it has been replaced with 23.

I would be grateful in any help in fixing this issue.

Thank you!"

[JamesCherrill]

Your understanding is wrong in that the key/value pair is not replaced, just the value. The API doc says
"If the map previously contained a mapping for the key, the old value is replaced."
Your equals method defines two Accounts as being the same if the name fields are equal, so although you have two different Accounts the second is seen as the same key. Thus the key is left unchanged (ie the first Account) and the value is updated.

[sciprog22]

Thank you, that makes it very clear!!