import java.awt.Color;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.UIManager;

public class FocusHighlighter implements FocusListener {

    @Override
    public void focusGained(FocusEvent e) {
        e.getComponent().setBackground(Color.YELLOW);
    }

    @Override
    public void focusLost(FocusEvent e) {
        e.getComponent().setBackground(UIManager.getColor("TextField.background"));
    }
}