Question

suggestBox.addKeyUpHandler( new KeyUpHandler() {
  public void onKeyUp(KeyUpEvent event) {
    if (event.getNativeKeyCode() == KeyCodes.KEY_ENTER) { 
      String boxText = suggestBox.getText();
      if (!boxText.equals("")) {
        suggestPanel.add(checkBoxFactory(boxText, candidateNames));
        suggestBox.setText("");
      }
    }
  }
});

I haven’t been able to grasp why java forces me to declare the ArrayList (candiateNames) as final. Why is that?

Answer 1

It’s an inner class, passed into addKeyUpHandler — all variables referenced outside an inner class need to be declared as final to be used within the inner class. This is because the local class instance must maintain a separate copy of the variable, as it may out-live the function; so as not to have the confusion of two modifiable variables with the same name in the same scope, the variable is forced to be non-modifiable.

Simply do final {type} {new-varname} = {old-varname}; before calling the method that uses the inner class, and then use {new-varname} inside that.