Developing Swing applications - IntelliJ IDEA in Action - page 364

Listing 10.4 The Currency.java class

package com.acme.conversion.currency;

import java.util.HashSet;

public final class Currency {
private static Set allCurrenciesSet;

static {
allCurrenciesSet = new HashSet();
allCurrenciesSet.add("USD");
allCurrenciesSet.add("CDN");
}

public static Iterator getCurrencies() {
return allCurrenciesSet.iterator();
}
}

Now, you can rely on the Currency class to provide a list of currencies you support.
You can query the Currency class for its list of known currencies and then add a
string into the JC omboBoxes' option lists for each occurrence. Listing 10.5 shows
the first version of the form class's constructor.

Listing 10.5 The ACMEGUI.java constructor, which populates the GUI's

JComboBoxes

...
public ACMEGUI() {
Iterator currencies = Currency.getCurrencies();
while (currencies.hasNext()) {
String currency = (String)currencies.next();
fromCurrency.addItem(currency);
toCurrency.addItem(currency);
}
}
...

10.6.3 Implementing the Convert functionality

In addition to initializing the JC omboBoxes with data, you need to add another
significant piece of functionality: the power behind the Convert button. When
this button is clicked, the GUI should collect the amount and the currencies from