Error on line 26,30, and 47

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class check_tut extends JFrame{
    /**
     * Author: Zachary Williams
     */
    private static final long serialVersionUID = 1L;
    private JTextField tf;
    private JCheckBox bold;
    private JCheckBox italics;

    public check_tut(){
        super("Check Box Tut");
        setLayout(new FlowLayout());

        tf = new JTextField("This is a sentence", 20);
        tf.setFont(new Font("Serif", Font.PLAIN, 14));
        add(tf);

        bold = new JCheckBox("Bold");
        italics = new JCheckBox("italics");
        add(bold);
        add(italics);

        HandlerClass handler = new HandlerClass();
        bold.addItemListener(handler);
        italics.addItemListener(handler);
    }
    private HandlerClass implements ItemListener{
        private Font font;
        public void itemStateChanged(ItemEvent event){


            if(bold.isSelected() && italics.isSelected()){
                font = new Font("Serif", Font.BOLD + Font.ITALIC, 14);
            }else if(bold.isSelected()){
                font = new Font("Serif", Font.BOLD, 14);
            }else if(italics.isSelected()){
                font = new Font("Serif", Font.ITALIC, 14);
            }else{
                font = new Font("Serif", Font.PLAIN, 14);
            }
            tf.setFont(font);
        }
    }
}