How to work with adapter classes

• An adapter class is a class that implements all the methods of a listener interface as empty methods. Then, an event listener class that inherits an adapter class must override only the methods that the program needs.

Common adapter classes

The AutoSelect class using FocusAdapter

public class AutoSelect extends FocusAdapter
{
    public void focusGained(FocusEvent e)
    {
        if (e.getComponent() instanceof JTextField)
        {
            JTextField t = (JTextField) e.getComponent();
            t.selectAll();
        }
    }
}

The NumFilter class using KeyAdapter

public class NumFilter extends KeyAdapter
{
    public void keyTyped(KeyEvent e)
    {
        char c = e.getKeyChar();
        if (   c != '0' && c != '1' && c != '2'
            && c != '3' && c != '4' && c != '5'
            && c != '6' && c != '7' && c != '8'
            && c != '9' && c != '.' && c != '+'
            && c != '-')
            e.consume();
    }
}