Java-如何对多个JTextField使用单个FocusListener？

Question

Some background: I'm a fairly experienced C++ programmer, but I'm currently teaching myself Java.

I have an application with several JTextFields, and I want the content of a field to be highlighted when I click on it. I know I can write a simple inline FocusAdapter for each one, but I'd like to write a single nested class that is used for each JTestField's addFocusListener. I figured out the following code works:

    private class textFieldFocusListener extends FocusAdapter {
    @Override
    public void focusGained(FocusEvent arg0) {
        ((JTextComponent) arg0.getComponent()).selectAll();
        }   
    }

...but that JTextComponent cast troubles me a little bit. In C++ casts are frowned upon, and I'm not familiar with the Best Practices of Java.

So, is this solution with the cast to JTextComponent "good" Java coding, or is there a better/cleaner solution?

Answer 1

JTextComponent cast troubles me a little bit

This is fine to do, as long as you take care to only add the FocusListener to JTextComponents such as JTextFields. If you want to be extra careful, you could always do an instanceof check,

Component comp = e.getComponent();
if (!(e instanceof JTextComponent)) {
   return;
}

but likely it's not necessary.

Perhaps better: create a method that adds the FocusListener and that only accepts JTextComponent as its parameter.

Answer 2

test if arg0 is a JTextComponent

private class textFieldFocusListener extends FocusAdapter {
    @Override
    public void focusGained(FocusEvent arg0) {
        if (arg0 instanceOf JTextComponent) {
           ((JTextComponent) arg0.getComponent()).selectAll();
          }
        }   
    }

Answer 3

只需创建一个所有听众都调用它的函数即可。