final StaticTextItem resultsValueItem = new StaticTextItem("resultsValue", "Results Value");
final StaticTextItem resultsUnitItem = new StaticTextItem("resultsUnits", "Results Units");
ButtonItem button = new ButtonItem("convertItem", "Convert");
button.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
MeasurementUnits units = MeasurementUnits.valueOf(unitsMenu.getValueAsString());
String value = textItem.getValueAsString();
MeasurementNumericValueAndUnits vu = MeasurementParser.parse(value, units);
resultsValueItem.setValue(vu.getValue().toString());