Can't store Object in HashMap

Question

I'm trying to create a SecureDataContainer with HashMap so defined: HashMap: ()>
Where KeyCouple is a class defined by me which contains the couple to access to the Vector associated to that couple. Now when i create a couple of HashMap in this method

private Map<KeyCouple,Vector<E>> DBUsers;

public void createUser(String Id, String passw) throws 
     UserAlreadyPresent {
     if(Id.isEmpty() || passw.isEmpty()) throw new IllegalArgumentException();
     if(existsUser(Id)) throw new UserAlreadyPresent(Id);

     KeyCouple u = new KeyCouple(Id, passw);
     DBUsers.put(u, new Vector<>());
}

Now, in main class, I Run the following code:

private static void testContainer(SecureDataContainer<String> container){
    try {
            container.createUser("Name","pwd");
    } catch (UserAlreadyPresent e) {
            System.out.println("User already present");
    }
...

To create the user "Name" with the Password "pwd". But When i put something in the Vector associated to the couple created using my "put" method:

public boolean put(String Owner, String passw, E data) throws NoUserException {
    if(Owner == null || passw == null || data == null) throw new NullPointerException();
    if(Owner.isEmpty() || passw.isEmpty()) throw new IllegalArgumentException();

    KeyCouple user = new KeyCouple(Owner,passw);
    if(DBUsers.containsKey(user)){
        Vector<E> aux = DBUsers.get(user);
        return aux.add(data);
    }else{
        throw new NoUserException("No user");
    }
}

In main class, I call the method:

    try {
        container.put("Name", "pwd", someData of type E);
    } catch (NoUserException e){
        abort("no user");
    }

and it abort in every case, going even in the catch branch and printing "no user".

What does this means?

Try to override equals and hashcode for you KeyCouple class. — imprezzeb, Nov 09 '18 at 00:46
you can autogenerate equals and hashcode if you are using IDE. Please also check the below sample for you keyCouple class. — imprezzeb, Nov 09 '18 at 02:12

score 1 · Accepted Answer · answered Nov 09 '18 at 02:11

You can check the sample KeyCouple class with equals and hashcode.

public class KeyCouple {   

    private String name;    

    private String pwd;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        KeyCouple keyCouple = (KeyCouple) o;
        return Objects.equals(name, keyCouple.name) &&
                Objects.equals(pwd, keyCouple.pwd);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, pwd);
    }
}

score 0 · Answer 2 · answered Nov 09 '18 at 00:44

0

Your passwords are different. You created it with Pwd, and in your main class you use pwd

answered Nov 09 '18 at 00:44

Justin

1,356
2
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16

no sorry, just my bad writing in the StackOverflow editor – Fulvio Nov 09 '18 at 00:45
maybe try and override the equals function in KeyCouple assuming it's a custom class. – Justin Nov 09 '18 at 00:46

score 0 · Answer 3 · answered Nov 09 '18 at 02:20

every use of new creates a new object in the heap. while you have stored one instance of KeyCouple as key in the hashmap, you are trying to match it with a different instance of KeyCouple. the hash code generated for each instance of user would be different. thus, java is not able to match them. one solution would be to override the hashCode method in KeyCouple Class.

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

score 0 · Answer 4 · answered Nov 09 '18 at 02:38

You'll need to overwrite the equals and hashcode methods of KeyCouple.

I'd suggest you to use any IDE to auto-generate them for you.

KeyCouple user = new KeyCouple(Owner,passw);

This creates a new user object and you insert this into the map. And the next time you are creating another new Object (which is never equal to the already created Object unless you explicitly override equals/hashcode).

Please refer this for further explanation.

Why do I need to override the equals and hashCode methods in Java?

Can't store Object in HashMap

4 Answers4