how to check if an object already exists

[oll3i]

how to check if an object already exists and return reference to that object

[oll3i]

public boolean equals(Object o) {
    if (!(o instanceof Klient)) return false;
    Klient k = (Klient) o;
    return  nazwa ==k.nazwa && pieniadze == k.pieniadze;
  }
 

i did it like this is it okey

[JosAH]

public boolean equals(Object o) {
    if (!(o instanceof Klient)) return false;
    Klient k = (Klient) o;
    return  nazwa ==k.nazwa && pieniadze == k.pieniadze;
  }
 

i did it like this is it okey

If 'nazwa' and 'pieniadze' can be compared for equality using the '==' operator,
I think all is fine. If one of them is an object (i.e. not a primitive) you have to
compare those members using the equals() method again (think about Strings).
Don't forget to implement the hashCode() method too.

kind regards,

Jos

[oll3i]

but i have a problem here cos when one button is clicked i create a client and add it to the list then when other button is clicked that client adds to the cart but the client created with the first button is not seen in the other portion of the code (the code for the second button)

[JosAH]

but i have a problem here cos when one button is clicked i create a client and add it to the list then when other button is clicked that client adds to the cart but the client created with the first button is not seen in the other portion of the code (the code for the second button)

That's an entirely different problem. Forget about GUIs for now and just take
care that your equals() and hashCode() methods are correctly implemented.
Build a little main() method that sticks Klients in a List and tries to find them
again afterwards. If all that works, build your GUI.

kind regards,

Jos

[oll3i]

i wdnt have to add to the list if the equals method worked :)

[JosAH]

i wdnt have to add to the list if the equals method worked :)

True, but my guess is that your equals() method doesn't work yet and the less
circumstancial code around (such as buttons etc.) the less difficult it is to
debug your code. Note that a list can store duplicate objects (the equals()
method returns true) so you should test before adding:

if (!list.contains(klient)) list.add(klient);

... or you could use a Set for this but still then: your equals() method should
work correctly.

kind regards,

Jos

[oll3i]

the equals method works i compared two clients

[JosAH]

the equals method works i compared two clients

Good; did you override the hashCode() method too?

kind regards,

Jos

[oll3i]

public int hashCode()
{
int result = 17;
result = 37 * result + pieniadze.hashCode();
result = 37 * result + nazwa.hashCode();
 
return result;
}
 

pieniadze is a double and i have a problem
and i dont know if it a good definition

[JosAH]

public int hashCode()
{
int result = 17;
result = 37 * result + pieniadze.hashCode();
result = 37 * result + nazwa.hashCode();
 
return result;
}
 

pieniadze is a double and i have a problem
and i dont know if it a good definition

primitives don't have methods so 'double.hashCod e()' doesn't make sense; but
why not simply cast the double value to an int and use that as the double's
hash value:

int result = 17;
result = 37 * result + (int)pieniadze;
result = 37 * result + nazwa.hashCode();

Is 'nazwa' an object? If so you have to use its 'equals()' method in your own
'equals()' method (see a couple of replies back).

kind regards,

Jos