How to change selection of comboBox

Question

So, I want to change the selected value of comboBox depending on values I read from my object. This is what I have so far:

public String[] waluta=new String[] {"EUR","PLN","USD"};

public GameEditFrame(int index) {

    ...

    JComboBox walutaBox = new JComboBox(waluta);
    String tmp=main.katalog.gra.get(index).cena.getWaluta();

    if (tmp=="EUR" || tmp==null){
        walutaBox.setSelectedItem(waluta[0]);
    }else if (tmp=="PLN"){
        walutaBox.setSelectedItem(waluta[1]);
    }else if (tmp=="USD"){
        walutaBox.setSelectedItem(waluta[2]);
    }

    ...
}

Sadly, this is not working. Any ideas?

---

EDIT: SOLVED

Thanks to ZouZou and MadProgrammer comments I've modded previous code. Now it looks like this and it works fine:

public String[] waluta=new String[] {"EUR","PLN","USD"};

public GameEditFrame(int index) {

    ...

    JComboBox walutaBox = new JComboBox(waluta);
    String tmp=main.katalog.gra.get(index).cena.getWaluta();

    if (tmp==null)
        tmp="EUR";

    walutaBox.setSelectedItem(tmp);

    ...

}